Abstract:
A novel and improved EPDM formulation for a solid propellant rocket motor is described wherein hexadiene EPDM monomer components are replaced by alkylidene norbornene components and with appropriate adjustment of curing and other additives functionally-required rheological and physical characteristics are achieved with the desired compatibility with any one of a plurality of solid filler materials, e.g. powder silica, carbon fibers or aramid fibers, and with appropriate adhesion and extended storage or shelf life characteristics.

Description:
This application claims the benefit of the priority from Provisional Application Nos. 60/115,855, 60/115,856, 60/115,859 and 60/115,857 filed on Jan. 13, 1989. 
    
    
     ORIGIN OF THE INVENTION 
     The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of contract NAS 8-38100 awarded by the National Aeronautics and Space Administration (NASA) and contract N00030-97-C-0100 awarded by the U.S. Department of the Navy. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a novel composition and method for providing insulation for solid propellant rocket motors, and more particularly to EPDM compositions having fibrous components such as carbon fibers or powder fillers such as silica, or also containing Kevlar reinforcing fibers and suitable for internal and external insulation applications on such rocket motors. 
     2. Background and Description of the Related Art 
     It is generally accepted current industry practice to prepare insulations for solid propellant rocket motors from a polymeric base importantly composed of an EPDM (ethylene-propylene-diene monomer) terpolymer blend and containing as one of the diene monomer components of the EPDM blend a 1,4-hexadiene (HD). 
     This EPDM terpolymer, which is commonly designated as the primary EPDM terpolymer since it is present in a higher concentration than the secondary EPDM terpolymer, has been established as a standard for solid propellant rocket motor insulations due to its superior ablation characteristics, excellent physical properties and processability. 
     For instance, an exemplary carbon fiber-filled rocket motor insulation composed of NORDEL 1040 as the primary terpolymer is commonly known in the industry as the STW4-2868 thermal insulation and has the following composition as shown in Table 1: 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 STW4-2868 THERMAL INSULATION FORMULATION 
               
               
                 (carbon fiber; parts by weight) 
               
             
          
           
               
                   
                   
                 Parts by 
               
               
                 Ingredient 
                 Function 
                 Weight 
               
               
                   
               
               
                 NORDEL 1040 
                 Primary EPDM terpolymer base 
                 80  
               
               
                 Neoprene FB 
                 Secondary polymer base 
                 20  
               
               
                 Zinc oxide 
                 Activator 
                 5 
               
               
                 Sulfur 
                 Curative 
                 1 
               
               
                 HAF carbon black 
                 Pigment 
                 1 
               
               
                 MBT 
                 Accelerator 
                 1 
               
               
                 AGERITE Resin D 
                 Antioxidant 
                 2 
               
               
                 AGERITE HPS 
                 Antioxidant 
                 1 
               
               
                 Tellurac 
                 Accelerator 
                   0.50 
               
               
                 Sulfads 
                 Accelerator 
                   0.75 
               
               
                 VCM carbon fibers 
                 Filler 
                 41  
               
               
                 Total Parts by Weight 
                   
                  153.25 
               
               
                   
               
             
          
         
       
     
     Alternatively, solid rocket motor insulations are also composed of compositions employing finely divided powder silica as a filler, with or without the added presence of a fibrous reinforcing agent. 
     Exemplary silica-filled rocket motor insulations have also included NORDEL 1040 and NORDEL 2522 as the primary terpolymer in their formulations and the resulting compositions are respectively commonly known in the industry as the 053A and DL1375 thermal insulations. They have the following compositions shown in Table 2: 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 THERMAL INSULATION FORMULATION 
               
               
                 (silica filled; parts by weight) 
               
             
          
           
               
                   
                   
                 DL1375 
                 053A 
               
               
                   
                   
                 (parts by 
                 (parts by 
               
               
                 Ingredient 
                 Function 
                 weight) 
                 weight) 
               
               
                   
               
               
                 NORDEL 1040 
                 Primary EPDM 
                   
                 80  
               
               
                   
                 terpolymer base 
               
               
                 NORDEL 2522 
                 Primary EPDM 
                 80  
               
               
                   
                 terpolymer base 
               
               
                 Neoprene FB 
                 Secondary 
                 20  
                 20  
               
               
                   
                 polymer base 
               
               
                 Zinc oxide 
                 Activator 
                 5 
                 5 
               
               
                 Sulfur 
                 Curative 
                 1 
               
               
                 AGERITE Resin D 
                 Antioxidant 
                 2 
                 2 
               
               
                 AGERITE HPS 
                 Antioxidant 
                 1 
                 1 
               
               
                 Captax 
                 Accelerator 
                 1 
                 1 
               
               
                 Tellurac 
                 Accelerator 
                   0.5 
                   0.5 
               
               
                 Sulfads 
                 Accelerator 
                   0.75 
                   0.75 
               
               
                 HiSil 233 
                 Filler 
                  35.5 
                  35.5 
               
               
                 Total Parts by Weight 
                   
                  146.75 
                  146.75 
               
               
                   
               
             
          
         
       
     
     In addition, an EPDM terpolymer comprising the HD monomer is sold under the tradename NORDEL 2722E. An exemplary silica-filled rocket motor insulation comprising NORDEL 2722E as the secondary terpolymer is commonly known in the industry as the DL1552A thermal insulation and has the following composition as shown in Table 3: 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 DL1552A THERMAL INSULATION FORMULATION WITH SILICA 
               
             
          
           
               
                   
                   
                 Parts by 
               
               
                 Ingredient 
                 Function 
                 Weight 
               
               
                   
               
             
          
           
               
                 Buna EP T 3950 (Bayer Corp., Fiber, 
                 Primary EPDM 
                 75 
               
               
                 Additives and Rubber Division of 
                 terpolymer base 
               
               
                 Orange, Texas) 
               
               
                 NORDEL 2722E (DuPont Dow 
                 Secondary EPDM 
                 20 
               
               
                 Elastomers) 
                 terpolymer base 
               
               
                   
                 with high 
               
               
                   
                 ethylene content 
               
               
                 WINGTACK 95 (hydrocarbon resin) 
                 Tackifier 
                 7 
               
               
                 (Goodyear Tire and Rubber Co., 
               
               
                 Chemical Division of Beaumont, 
               
               
                 Texas) 
               
               
                 IRGANOX 1010 (tetrakis[methylene-3- 
                 Antioxidant 
                 1 
               
               
                 (3′-5′-di-tert-butyl-4′-hydroxyphenyl) 
               
               
                 proprionate]methane) (Ciba Specialty 
               
               
                 Chemicals, Additives Division, 
               
               
                 Tarrytown, N.Y.) 
               
               
                 TRYCOL DA-6 (decyl 
                 Wetting agent 
                 0.5 
               
               
                 polyoxyethylene alcohol)(Chemical 
               
               
                 Associates, Inc. of Copley, Ohio) 
               
               
                 Stearic acid (including palmitic acid) 
                 Cure activator 
                 1 
               
               
                 (Harwick Standard Distribution Corp. 
               
               
                 of Akron, Ohio) 
               
               
                 HiSil 233 (silica hydrate)(PPG 
                 Reinforcing filler 
                 45 
               
               
                 Industries, Inc. of Lake Charles, 
               
               
                 Louisiana) 
               
               
                 Aluminum oxide C (Al 2 O 3 )(Degussa 
                 Reinforcing filler 
                 0.3 
               
               
                 Corporation of Ridgefield Park, N.J.) 
               
               
                 N330 carbon black (Columbian 
                 Pigment and 
               
               
                 Chemicals Co. of Marietta, Ga.) 
                 reinforcing filler 
               
               
                 KALENE 1300 (butyl gum elastomer) 
                 Co-vulcanizing 
                 20 
               
               
                 (Hardman Division of Harcros 
                 plasticizer 
               
               
                 Chemicals, Inc. of Belleville, N.J.) 
               
               
                 HYPALON 20 (chlorosulfonated 
                 Cure activator 
                 5 
               
               
                 polyethylene)(DuPont Dow 
               
               
                 Elastomers) 
               
               
                 AGERITE Resin D (polymerized 
                 Antioxidant 
                 0.25 
               
               
                 trimethyl dihydroquinone)(R.T. 
               
               
                 Vanderbilt Co., Inc. of Buena Park, 
               
               
                 Ca.) 
               
               
                 TZFD-88p (zinc oxide dispersed in an 
                 Cure activator 
                 2 
               
               
                 EPDM binder)(Rhein Chemie Corp. of 
               
               
                 Trenton, N.J.) 
               
               
                 SP 1056 (bromomethyl alkylated 
                 Curing agent 
                 15 
               
               
                 phenolic resin)(Schenectady Int&#39;l, Inc. 
               
               
                 of Schenectady, N.Y.) 
               
               
                 Total Parts by Weight 
                   
                 193.05 
               
               
                   
               
             
          
         
       
     
     An exemplary aramid fiber filled rocket motor insulation comprising NORDEL 1040 is commonly known in the industry as R196 thermal insulation and has the following composition as shown in Table 4: 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 R196 THERMAL INSULATION FORMULATION WITH KEVLAR 
               
             
          
           
               
                   
                   
                 Parts by 
               
               
                 Ingredient 
                 Function 
                 Weight 
               
               
                   
               
             
          
           
               
                 NORDEL 1040 (EPDM terpolymer) 
                 Polymer base 
                 80 
               
               
                 NATSYN 2200 (polyisoprene) 
                 Polymer base 
                 20 
               
               
                 (Goodyear Tire and Rubber Co., 
               
               
                 Chemical Division of Akron, Ohio) 
               
               
                 WINSTAY S (styrenated phenols) 
                 Antioxidant 
                 1.0 
               
               
                 (Goodyear Tire and Rubber Co., 
               
               
                 Chemical Division of Akron, Ohio) 
               
               
                 Dechlorane Plus 515 
                 Flame retardant 
                 40 
               
               
                 (1,2,3,4,7,8,9,10,13,13,14,14- 
               
               
                 dodecachloro- 
               
               
                 1,4,4a,5,6,6q,7,10,10a,11,12,12a- 
               
               
                 dodecahydro-1,4,7,10- 
               
               
                 dimethanodibenzo (a,e) cyclooctene) 
               
               
                 (Occidental Chemical Corporation of 
               
               
                 Dallas, Texas) 
               
               
                 Antimony oxide (Sb 2 O 3 )(Harcros 
                 Flame retardant/- 
                 20 
               
               
                 Chemicals, Inc. of Kansas City, 
                 filler 
               
               
                 Kansas) 
               
               
                 ¼″ KEVLAR fiber (aramid staple fiber) 
                 Fiber 
                 20 
               
               
                 (E.I. duPont de Nemours and Co., of 
               
               
                 Wilmington, Delaware) 
               
               
                 VAROX DBPH-50 (2,5-dimethyl-2,5- 
                 Curing agent 
                 2.5 
               
               
                 di(t-butylperoxy)hexane on a carrier) 
               
               
                 (R.T. Vanderbilt Co., Inc. of Buena 
               
               
                 Park, Ca.) 
               
               
                 Total Parts by Weight 
                   
                 183.5 
               
               
                   
               
             
          
         
       
     
     Numerous past efforts to develop effective replacements for these standard solid rocket motor insulation formulations have not been successful. 
     The only manufacturer currently producing the foregoing primary EPDM terpolymer in adequate quantities to meet the demands of the rocket motor insulation industry is DuPont Dow Elastomers of Beaumont, Tex., which markets and sells an EPDM terpolymer comprising the HD monomer under the tradename NORDEL 1040 and Nordel 2522. 
     However, the ability of the industry to produce STW4-2968, DL1375, 053A, DL1552A, R196 and other thermal insulations containing NORDEL 1040 and NORDEL 2522, and NORDEL 2722E as a primary or secondary EPDM terpolymer has recently been placed in jeopardy due to the announcement by DuPont of its intention to cease production of NORDEL 1040, 2522, 2722E and, generally, other EPDM polymers formed from 1,4-hexadiene. There is therefore a need in this industry, previously not satisfied, to find an effective alternate or a replacement for the above-described standard STW4-2868, DL1375, 053A DLl1552A and R196 thermal insulations. Development and formulation of a suitable primary EPDM terpolymer replacement is especially critical for these discontinued NORDEL insulation formulations. 
     The requirements for an acceptable, functionally effective, insulation for solid propellant rocket motors are well known to be quite severe due to the extreme conditions to which the insulation is exposed. These conditions not only include exceedingly high temperatures but also severe ablative effects from the hot particles (as well as gases) that traverse and exit the rocket motor interior. Unless the insulation will withstand such conditions, catastrophic failure may (and has) occur. 
     U.S. Pat. No. 3,347,047, an early patent describing asbestos fiber filled insulations, states that flame temperatures encountered in the combustion of propellants, particularly when used as source of propulsion, necessitating the confinement of the gases of combustion and ultimate release thereof through orifices, are usually accompanied by extremely turbulent flow conditions. All of these features place considerable stress and strain upon the member defining the escape passageway. While the combustion of the propellant in the case of rockets and the like will usually be of short duration, the temperatures and turbulence encountered have been found to very easily destroy even the strongest and most exotic alloys formed of iron, steel, titanium, magnesium, silicon, chromium, beryllium and the like. As a consequence, the projectile structure fails leading to total destruction thereof through explosion or in the event that only the exit passageway is destroyed, the projectile proceeds in an erratic uncontrollable path since its trajectory or path is at least in part dependent upon the contour of the passageway through which pass the gaseous products of combustion. That statement still remains fully applicable today. 
     Therefore any replacement insulation should exhibit at least comparable temperature resistant and ablation characteristics and rheological and physical properties (e.g., Mooney viscosity) at least equivalent to that of STW4-2868, DL1375, 053A, DL1552A and R196, yet should not otherwise significantly alter the formulation techniques employed for the production of the such rocket motor thermal insulation. Additionally, due to the large and growing quantities of solid propellant rocket motor insulation required by the industry, any such replacement EPDM terpolymer candidate should be abundantly available now and into the foreseeable future. 
     In addition, any replacement EPDM or like terpolymer should satisfy a number of other requirements including wettability of and bond strength with such diverse filler additives as a carbon fiber, aramid fiber, and a silica powder. It is also necessary that such additives be substantially homogeneously dispersed throughout the insulation composition as it is being produced. While standard mixing devices can be employed in the practice of this invention, such as a Banbury mixer, it is a common experience that substantially homogeneous distribution of fibrous additives is not achieved, or achieved only with difficulty, with many elastomeric compositions. Difficulties have been described as in, for instance, during mixing of the components, it can be observed that premature vulcanization may occur as well as other problems that may impede, or entirely frustrate, effective distribution of the various additives which are essential to the ultimate production of the insulation. 
     Further, once formulated, the elastomeric composition must also possess acceptable shelf life characteristics such that it remains sufficiently pliable, without becoming fully cured, until used in application to the rocket motor casing. This requirement is essential because the production of a given lot of insulation may have to wait in storage for a number of months prior to use. Typically, the insulation may be stored in large rolls in an uncured, or at most a partially cured, state until ready for use. A number of curing agents are well known and are conventionally employed but still must be compatible with the overall EPDM formulation to permit satisfactory shelf life. This in turn requires a balancing of curing agent activity. 
     In addition, the formulated insulation should be substantially odorless for obvious reasons and this can require special adjustment of the curing agent components. 
     After application to the interior (or if desired the exterior) of the rocket motor casing, and subsequent curing thereof, an acceptable insulation must also exhibit satisfactory bonding characteristics to a variety of adjacent surfaces. Such surfaces include the internal surface of the rocket motor casing itself and the insulation must also exhibit adequate bonding characteristics between itself and the propellant grain, typically with an intermediate liner surface. In turn, the propellant grain in a solid propellant rocket motor is composed of a variety of materials notably including still another elastomer, various combustible materials, and such additional components as aluminum particles. 
     A functionally acceptable solid propellant rocket motor insulation must meet those requirements and must also survive aging tests. Such rocket motors may be fully fabricated even many months before actual firing, and for tactical weapons especially sometimes even more than a year or even a plurality of years. For instance, strategic missiles may be stored in silos or submarine launch tubes for decades. Over that period of time, the insulation must continue to remain fully functional without unacceptable migration of its components to or from adjacent interfacial surfaces and adequately retain its elastomeric characteristics to prevent brittleness. This requirement also needs to be satisfied under wide temperature variations. The vibration and physical stress placed on a rocket motor at the time of launch, whether a ground launch or an air firing, is exceedingly high, and brittleness and cracking in the insulation is effectively intolerable, whether from premature or gradual overcure or whatever cause. Even at the end of the burn of the propellant grain within the rocket motor casing the insulation must remain substantially and functionally intact to avoid potentially catastrophic failures of the entire launch vehicle. 
     In turn, this means that the insulation composition must meet the ablation limits for protection of the casing throughout the propellant burn without adding undue weight to the motor. 
     A number of past patents have been granted proposing various solutions to the insulation formulation problem. These include U.S. Pat. No. 3,421,970 (generically describing elastomeric formulations with asbestos); U.S. Pat. No. 3,562,304 (generically describing an elastomeric formulation with asbestos fibers); U.S. Pat. No. 3,637,576 (describing an EPDM formulation with a norbornene component with asbestos fibers); U.S. Pat. No. 4,492,779 (generically describing elastomeric formulations with Kevlar fibers); U.S. Pat. No. 4,514,541 (generically a du Pont “master batch” formulation with Kevlar fibers, but not an insulation); U.S. Pat. No. 4,550,130 (generically describing a moldable carboxylic acid modified EPDM to enhance affinity to various fillers); U.S. Pat. No. 4,878,431 (generically describing an elastomeric formulation using the EPDM Nordel 1040, with Kevlar fibers); U.S. Pat. No. 5,364,905 (describing a technique for the in situ polycondensation formation of aramid fibers, but not referring to rocket motor insulations); U.S. Pat. No. 5,498,649 (describing a polyamide/maleic anhydride modified EPDM with Kevlar fibers for a rocket motor insulation); U.S. Pat. No. 5,821,284 (a Kevlar fiber filled insulation containing an EPDM illustrated by Nordel 2522 in combination with ammonium salts); and U.S. Pat. No. 5,830,384 (generically referring to EPDM&#39;s with a “dry water” silica additive for cooling purposes). None of these patents address nor effectively solve the problem faced by the present invention. In fact the frequent reference to Nordel 1040 or Nordel 2522 serves to confirm the observation that these particular elastomers are well-nigh the standard in the rocket motor insulation industry. 
     Accordingly, the search for a functionally satisfactory elastomeric insulation composition requires discovery and implementation of an extraordinarily complex combination of characteristics. The criticality of the material selection is further demonstrated by the severity and magnitude of the risk of failure. Most insulations are of necessity “man-rated” in the sense that a catastrophic failure can result in the loss of human life—whether the rocket motor is used as a booster for launch of the space shuttle or is carried tactically underneath the wing of an attack aircraft. The monetary cost of failure in satellite launches is well-publicized and can run into the hundreds of millions of dollars. 
     One well known potential point of failure is the appearance of voids or cracks in the insulation which could lead to the penetration of the rocket motor casing itself. The resultant dispersion of hot gases may not only lead to destruction of the motor generally or can at least lead to its being thrown of its intended course or trajectory with several unhappy results. In such events, either the vehicle itself will self-destruct, or will be intentionally destroyed, or the satellite will be launched into a useless orbit. 
     Therefore, one of the most difficult tasks in the solid propellant rocket motor industry is the development of a suitable, acceptable insulation composition that will meet and pass a large number of test criteria to lead to its acceptability. 
     Furthermore, any replacement EPDM terpolymers should not be susceptible to obsolescence issues nor discontinuance in future supply thereof. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of this invention to address a crucial long-standing need in the industry for an acceptable substitute for the STW4-2868, DL1375, 053A, DL1552A and R1961 insulations by providing a reformulated rocket motor thermal insulation notably comprising a suitable primary or secondary terpolymer replacement for the 1,4-hexadiene-based EPDM and one that minimizes the degree of modification to the existing formulation methods and also as to the ultimate functional properties of the STW4-2868, DL1375, DL 1552A, 053A and R196 thermal insulations. 
     In accordance with the principles of this invention, these and other objects of the invention are attained by the discovery and provision of a rocket motor insulation formulation comprising, as a primary or secondary terpolymeric base, an EPDM terpolymer formed from at least one alkylidene norbornene, especially ethylidene norbornene (ENB) as the diene component. 
     Exemplary EPDM terpolymers that may be used according to this invention comprise those having an alkylidene diene, particularly an ENB diene, component include KELTAN 4506, KELTAN 1446A, KELTAN 2308, NORDEL IP NDR-4520, and NORDEL IP NDR-4640, each of which may be substituted into the STW4-2868, DL1375, R196 and 053A insulation for the NORDEL 1040 without requiring significant modifications to the standard STW4-2868, DL1375, 053A, DL1552A and R196 thermal insulation formulation methods nor as to the resulting multitude of functionally acceptable properties. Other exemplary terpolymers include high-ethylene-content EPDM terpolymers formed from an ENB diene component are NORDEL IP NDR-3722p and BUNA EP T 2370, which may be substituted into the DL1552A for the NORDEL IP NDR-2722E without requiring significant modifications to the DL1552A formulation. Nordell IP NDR-3725 has also been used but the supplier (du Pont) has indicated that due to low demand it now prefers a different formulation, Nordel IP NDR-3722, with a lower diene content of about 0.5% versus about 2.5% for Nordel IP NDR-3725p. 
     It has now been found that only a small proportion of ENB diene component is sufficient for incorporation in such elastomers, say from about 2 to about 10 wt. %, preferably from about 2 to about 7 wt. %, and with the balance of the olefin content of the composition composed of ethylene and propylene, with the ethylene forming from about 40 to about 80 wt. %, preferably from about 50 to about 75 wt. %, and with the remainder being propylene. Trace amounts of other dienes may also be present to induce branching in the elastomer. Generally, the only significant modification that is required involves the selection of a less reactive curing agent to offset the higher reactivity (relative to HD) of ethylidene norbornene (ENB). Furthermore, NORDEL IP NDR-3722 and BUNA EP T 2370 are not presently foreseen as being susceptible to obsolescence issues. 
     Other objects, aspects and advantages of the invention will be apparent to those skilled in the art upon reading the specification and appended claims which, when read in conjunction with the accompanying drawings, explain the principles of this invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings serve to elucidate the principles of this invention. In such drawings: 
     FIG. 1 is a schematic cross-sectional view of a rocket motor depicting various regions in which the insulation of this invention may be applied; 
     FIG. 2 is a schematic of a char motor suitable for conducting the ablation tests reported herein; and 
     FIG. 3 is a cut-away view of a solid propellant rocket motor illustrating the outer case, the internal insulation layer, the propellant grain, and the insulation of the ignitor closure structure. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     As shown in schematic FIG. 1, and its components in FIGS. 1 a - 3   b,  illustrate the manner in which the inventive insulation may be applied to various parts of a rocket assembly. These include, but are not limited to, the system tunnel floor plate shear ply  10 , the LSC blast shield  12 , the stiffener stub hole plugs  14 , stiffener stub insulation  16 , the external joint weatherseal  18 , T-ring insulation  20 , aft dome internal insulation  22 , and center segment aft end internal insulation (underneath the flap)  24 . 
     In FIG. 2, the schematic cross-section of a char motor test assembly is illustrated wherein the propellant is contained in the beaker  30 , and low velocity insulation test specimens located at  32  upstream of the throat  34 , with medium velocity test specimens located in the section at  36  and with high velocity insulation test specimens located in the region  38 . Generally, such a char test motor assembly permits the location of a plurality of different insulation formulation test specimens about the circumference at any of locations  32 ,  36  or  38 , in the conventional manner. 
     FIG. 3 is a cut-away schematic view of a typical rocket motor illustrating the case  40 , the nozzle  42 , the propellant grain  44  with its center bore  46  and the internal insulation layer shown at  48 . The insulation of the ignitor closure structure is indicated at  50 . 
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with one embodiment of this invention, the inventive rocket motor insulation formulation comprises, as a primary polymeric base, an EPDM terpolymer in which the diene component of the EPDM is composed of at least one alkylidene norbornene, and in particular ethylidene norbornene (ENB). 
     The selected EPDM terpolymer should be substitutable into the STW4-2868, DL1375, 053A, DL1552A and R196, thermal insulation formulation (Tables 1 and 2) without requiring significant modification of the present techniques employed for the formulation thereof. It is a further highly desirable feature of the present invention that the insulation formulation may be composed of readily available commercial materials, provided that such compositions are properly assembled and blended together for the final insulation material. 
     Suitable EPDM terpolymers having an ENB diene component for use in this invention include, without limitation, and as stated above, KELTAN 4506, KELTAN 1446A, KELTAN 2308, each of which is available from DSM of the Netherlands, and NORDEL IP 4520 and NORDEL IP 4640, both of which are and continue to be available from DuPont Dow Elastomers. 
     These materials have the following respective contents as derived from the manufacturer&#39;s data literature: 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 ENB 
                 Ethylene 
                   
               
               
                   
                 Content 
                 Content 
                 Mooney 
               
               
                   
                 Wt % 
                 Wt % 
                 Viscosity 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Keltan 4506 
                 4.5 
                 54 
                 40 
               
               
                   
                 Keltan 1446A 
                 7 
                 59 
                 10 
               
               
                   
                 Keltan 2308 
                 2 
                 74 
                 24 
               
               
                   
                 Nordel IP 4520 
                 5 
                 51 
                 20 
               
               
                   
                 Nordel IP 4640 
                 5 
                 55 
                 40 
               
               
                   
                   
               
             
          
         
       
     
     The remaining content is propylene with traces of certain dienes used to produce branching in the molecular structure. 
     In accordance with another preferred embodiment, the secondary EPDM terpolymer is/are NORDEL IP NDR-3722 and/or Buna EP T 2370, which include ENB as their diene monomers and are respectively available from DuPont Dow and Bayer Corporation and manufactured in relatively large capacities. 
     An exemplary formulation is set forth in TABLE 5: 
     
       
         
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                   
                 Parts by 
               
               
                 Ingredient 
                 Weight 
               
               
                   
               
             
             
               
                 Primary EPDM terpolymer 
                 70-80 
               
               
                 Secondary EPDM terpolymer with ENB diene monomer 
                 15-25 
               
               
                 Tackifier 
                  5-10 
               
               
                 Antioxidant 
                 1-3 
               
               
                 Wetting agent 
                 0-1 
               
               
                 Curing activator 
                  5-10 
               
               
                 Silica filler 
                 40-50 
               
               
                 Pigment 
                 0-3 
               
               
                 Plasticizer 
                 15-25 
               
               
                 Curing agent 
                 10-20 
               
               
                   
               
             
          
         
       
     
     The primary EPDM preferably has a sufficiently high diene content to provide a more reactive polymer to decrease cure time. Preferably, the alkylidene diene content of the primary EPDM is in a range of about 2-12 wt %, more preferably about 10-12 wt %. Additionally, the primary EPDM terpolymer preferably has a medium ethylene content of from about 56 wt % to about 65 wt %. 
     In a more preferred embodiment, the primary and secondary terpolymer components, tackifier, antioxidant, wetting agent, curing activator, filler, pigment, plasticizer, and silica are the same as those set forth in Table 3 above and are present in the concentrations specified in Table 3. However, when following that formulation composition on simply a “drop in” basis, it was observed that an unsatisfactory scorch characteristic developed (e.g. a scorch time of about 5.9 minutes as against and 8 minute minimum time allowed per specification. Similarly, substituting Buna EP T 2370 in place of Nordel 2722E led to similar results of an unsatisfactory scorch time of 6.6 minutes and a high Mooney viscosity of 119. Consequently, according to this invention, a less reactive brominated phenolic resin curing agent, for instance, having a lower reactivity than that used in the DL1552A formulation (i.e., SP 1056 containing about 6 wt % bromine) was required and was selected in order to compensate for the observed higher reactivity of ENB. This then led to acceptable scorch characteristics and the use of cure temperatures of about 320° F. provided similar cure rates as were used for DL 1552A. The resulting physical properties were also acceptable. Preferably, the resin curing agent of the reformulated insulation formulation is SP 1055 (manufactured by Schenectady International), which contains about 3% bromine by weight. 
     It will be observed that these materials may have significant variations in specific norbornene content, and also in the ethylene/propylene content ratio as well as in the Mooney viscosity, yet each has been found to be effective if selected for use in production of a rocket motor insulation. 
     Adhesion-promoting secondary polymers that may also be used in the formulation include elastomer modifiers, especially polar polymers. Among suitable such secondary polymers are chlorosulfonated polyethylene, such as Hypalon 20 from DuPont Dow, and polychloroprene. Polychloroprene polymers are available from DuPont Dow under the tradenames Neoprene FB, Neoprene TW, and Neoprene GRT. 
     An exemplary plasticizer for the inventive formulation is the EPDM-based Trilene 67A (Uniroyal). 
     Tackifiers may also optionally be used. An example of a suitable tackifier is Akrochem P-133. 
     One or more antioxidants are also preferably included within the inventive insulation formulation. Preferred antioxidants include polymerized 1,2-dihydro-2,2,4-trimethylquinoline (Agerite Resin D) and mixed octylated diphenylamines (Agerite Stalite S), each of which is available from R. T. Vanderbilt Co. 
     Various powder silica fillers are well known in other elastomeric combinations and may be used, including HiSil 233. 
     An exemplary carbon fiber is VMC carbon fiber. 
     Suitable cure activators may include metal oxides, such as zinc oxide and magnesium oxide (e.g., Elastomag 170, from Morton Chemical Co.). 
     The curing package preferably includes at least one phosphate cure accelerator, including by way of example, Rhenocure AP-5, Rhenocure AP-7, Rhenocure AP-3, Rhenocure ZADT/G, and Rhenocure S/G, which are available from Rhein Chemie and Accelerator VS, available from Akro Chem. Additional cure accelerators that may be used in combination with the phosphate cure accelerator include butyl zimate, Altax, Akroform Delta P.M., Sulfads. While the use of Accelerator VS was initially unacceptable because of the foul odor problem it generated, it has also been now found that such formulations can be prepared with no significant odor when about 1.0 phr magnesium oxide is added thereto. 
     Sulfur curing agents are preferred for the formulation. A suitable sulfur-curing agent is Akrosperse IS-70 from Akro Chem. Elemental sulfur can also be used. 
     Batches of insulation containing silica powder generally may be formulated in an internal mixer with the following two-pass mix procedure. In the first pass, the mixer speed may be set to approximately 40 rpm and the all of the components other than the curing agents and accelerators are added to the internal mixer. (The silica was added last in the first pass.) The mixing may be performed at a temperature of about 300° F. Suitable mixing times depend on the temperature and mixing speed, and are ascertainable to the skilled artisan without an undue amount of experimentation. 
     In the second pass, the mixer speed was set to about 40 rpm. In a sequential manner, half of the master batch was added to the mixer, then the curatives were added, then the remaining half of the master batch was added to the mixer. The second mixing step was performed at a temperature of approximately 180° F. to 190° F. The material was sheeted out onto the laboratory mill and allowed to cool to room temperature prior to evaluating its rheological and physical properties. 
     The shaping and curing of the inventive insulation may be performed in accordance with techniques known in the art. 
     Exemplary new formulations containing a silica powder filler are set forth in TABLE 6 below with concentrations shown by weight. 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                 EXAMPLES OF SILICA FILLED EPDM INSULATION FORMULATIONS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Ingredient 
                 RDL5338 
                 RDL5342 
                 RDL5343 
                 RDL5347 
                 RDL5363 
                 RDL5255 
                 RDL5335 
                 RDL5201 
                 RDL5220 
                 RDL5370 
               
               
                   
               
               
                 Keltan 4506 
                 70.0 
                 73.0 
                 73.0 
                 55.0 
                 55.0 
                   
                   
                   
                   
               
               
                 Keltan 1446A 
                 20.0 
                 17.0 
                 17.0 
                   
                   
                   
                   
                   
                   
               
               
                 Keltan 2308 
                   
                   
                   
                 35.0 
                 35.0 
                   
                   
                   
                   
               
               
                 Nordel IP 4520 
                   
                   
                   
                   
                   
                   
                   
                 80.0 
                 80.0 
                 80.0 
               
               
                 Nordel IP 4640 
                   
                   
                   
                   
                   
                 80.0 
                 80.0 
                   
                   
               
               
                 Hypalon 20 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
                   
                   
                   
                   
               
               
                 Neoprene FB 
                   
                   
                   
                   
                   
                 20.0 
                 20.0 
                   
                   
               
               
                 Neoprene TW 
                   
                   
                   
                   
                   
                   
                   
                 20.0 
                 20.0 
               
               
                 Neoprene GRT 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 20.0 
               
               
                 Trilene 67A 
               
               
                 Kraton L-2203 
               
               
                 Akrochem P-133 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
                   
                   
                 5.0 
                 5.0 
                 5.0 
               
               
                 Agerite Resin D 
                   
                   
                   
                   
                   
                 2.0 
                 2.0 
                 2.0 
                 2.0 
                 2.0 
               
               
                 Agerite Stalite S 
                 2.0 
                 2.0 
                 2.0 
                 2.0 
                 2.0 
                   
                   
                   
                   
               
               
                 HiSil 233 
                 35.5 
                 35.5 
                 35.5 
                 35.5 
                 35.5 
                 35.5 
                 35.5 
                 37.0 
                 37.0 
                 37.0 
               
               
                 Elastomag 170 
                   
                   
                   
                   
                   
                   
                   
                 0.5 
                 0.5 
                 0.50 
               
               
                 Zinc Oxide 
                 3.0 
                 3.0 
                 3.0 
                 3.0 
                 3.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.00 
               
               
                 Butyl Zimate 
                 0.50 
                 0.50 
                   
                   
                   
                   
                   
                   
                 0.50 
               
               
                 Rhenocure AP-5 
                 3.50 
                 3.50 
                   
                   
                   
                   
                   
                   
                 3.50 
               
               
                 Rhenocure AP-7 
               
               
                 Rhenocure AP-3 
                   
                   
                   
                   
                   
                 2.90 
                   
                 3.85 
                   
                 3.85 
               
               
                 Rhenocure ZADT/G 
                   
                   
                   
                   
                   
                 0.80 
                   
                 1.00 
                   
                 1.00 
               
               
                 Rhenocure S/G 
                   
                   
                   
                   
                   
                 0.60 
                   
                 0.80 
                   
                 0.80 
               
               
                 Altax 
                   
                   
                 1.10 
                 1.10 
                 1.20 
                   
                 1.10 
                   
                   
               
               
                 Akroform Delta P.M. 
                   
                   
                   
                   
                 0.45 
                   
                 0.20 
                   
                   
               
               
                 Sulfads 
                   
                   
                   
                   
                 0.50 
                   
                   
                   
                   
               
               
                 Accelerator VS 
                   
                   
                 2.70 
                 2.70 
                   
                   
                   
                   
                   
               
               
                 Akrosperse IS-70 
                 1.10 
                 1.10 
                 1.20 
                 1.20 
                 1.40 
                   
                   
                   
                 1.00 
               
               
                 Sulfur 
                   
                   
                   
                   
                   
                 0.35 
                 0.45 
                 0.40 
                   
                 0.40 
               
               
                   
               
             
          
           
               
                 Ingredient 
                 RDL5380 
                 RDL5381 
                 RDL5194 
                 RDL5222 
                 RDL5273A 
                 RDL5298 
                 RDL5277 
                 RDL5279 
                 RDL5319 
                 RDL5320A 
               
               
                   
               
               
                 Keltan 4506 
               
               
                 Keltan 1446A 
               
               
                 Keltan 2308 
               
               
                 Nordel IP 4520 
                 80.0 
                 80.0 
                 90.0 
                 90.0 
                 90.0 
                 80.0 
                   
                   
                 40.0 
                 40.0 
               
               
                 Nordel IP 4640 
                   
                   
                   
                   
                   
                   
                 90.0 
                 90.0 
                 50.0 
                 50.0 
               
               
                 Hypalon 20 
                   
                   
                 10.0 
                 10.0 
                 10.0 
                 10.0 
                   
                   
                 10.0 
                 10.0 
               
               
                 Neoprene FB 
               
               
                 Neoprene TW 
               
               
                 Neoprene GRT 
                 20.0 
                 20.0 
               
               
                 Trilene 67A 
                   
                   
                   
                   
                   
                 10.0 
               
               
                 Kraton L-2203 
                   
                   
                   
                   
                   
                   
                 10.0 
                 10.0 
               
               
                 Akrochem P-133 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
                 9.0 
                 9.0 
                 5.0 
                 5.0 
               
               
                 Agerite Resin D 
                 2.0 
                 2.0 
                 2.0 
                 2.0 
                 2.0 
                 2.0 
                 2.0 
                 2.0 
               
               
                 Agerite Stalite S 
                   
                   
                   
                   
                   
                   
                   
                   
                 2.0 
                 2.0 
               
               
                 HiSil 233 
                 37.0 
                 37.0 
                 35.5 
                 35.5 
                 35.5 
                 36.5 
                 38.0 
                 38.0 
                 35.5 
                 35.5 
               
               
                 Elastomag 170 
                 0.50 
                 0.50 
               
               
                 Zinc Oxide 
                 4.00 
                 4.00 
                 3.00 
                 3.00 
                 4.00 
                 3.00 
                 3.00 
                 3.00 
                 3.0 
                 4.0 
               
               
                 Butyl Zimate 
                 0.50 
                   
                   
                 0.40 
                   
                 0.15 
                   
                   
                 0.40 
               
               
                 Rhenocure AP-5 
                 3.40 
                   
                   
                 3.15 
                   
                 4.45 
                   
                   
                 3.15 
               
               
                 Rhenocure AP-7 
                   
                   
                   
                   
                   
                   
                 3.00 
               
               
                 Rhenocure AP-3 
                   
                   
                 3.85 
               
               
                 Rhenocure ZADT/G 
                   
                   
                 1.00 
                   
                   
                   
                 0.90 
               
               
                 Rhenocure S/G 
                   
                   
                 0.80 
               
               
                 Altax 
                   
                 1.00 
                   
                   
                 1.00 
                   
                   
                 1.20 
                   
                 1.00 
               
               
                 Akroform Delta P.M. 
                   
                   
                   
                   
                   
                   
                   
                 0.25 
               
               
                 Sulfads 
                   
                   
                   
                   
                   
                   
                   
                 0.82 
               
               
                 Accelerator VS 
                   
                 2.70 
                   
                   
                 2.70 
                   
                   
                   
                   
                 2.70 
               
               
                 Akrosperse IS-70 
                   
                   
                   
                 0.95 
                 1.10 
                 1.34 
                 1.25 
                 1.40 
                 1.00 
                 1.00 
               
               
                 Sulfur 
                 0.50 
                 0.50 
                 0.40 
               
               
                   
               
             
          
           
               
                   
                 Ingredient 
                 RDL5350 
                 RDL5351A 
                 RDL5367 
                 RDL5185 
                 RDL5186 
                 RDL5205 
                 RDL5276 
               
               
                   
                   
               
               
                   
                 Keltan 4506 
               
               
                   
                 Keltan 1446A 
               
               
                   
                 Keltan 2308 
               
               
                   
                 Nordel IP 4520 
                 45.0 
                 45.0 
                 45.0 
                   
                   
                   
                   
               
               
                   
                 Nordel IP 4640 
                 45.0 
                 45.0 
                 45.0 
                 80.0 
                 80.0 
                 80.0 
                 80.0 
               
               
                   
                 Hypalon 20 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
               
               
                   
                 Neoprene FB 
               
               
                   
                 Neoprene TW 
               
               
                   
                 Neoprene GRT 
               
               
                   
                 Trilene 67A 
                   
                   
                   
                 10.0 
                 10.0 
                 10.0 
                 10.0 
               
               
                   
                 Kraton L-2203 
               
               
                   
                 Akrochem P-133 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
               
               
                   
                 Agerite Resin D 
                   
                   
                   
                 2.0 
                 2.0 
                 2.0 
                 2.0 
               
               
                   
                 Agerite Stalite S 
                 2.0 
                 2.0 
                 2.0 
               
               
                   
                 HiSil 233 
                 35.5 
                 35.5 
                 35.5 
                 35.5 
                 35.5 
                 35.5 
                 35.5 
               
               
                   
                 Elastomag 170 
               
               
                   
                 Zinc Oxide 
                 3.0 
                 4.0 
                 3.0 
                 3.0 
                 3.0 
                 3.0 
                 3.0 
               
               
                   
                 Butyl Zimate 
                 0.40 
                   
                   
                   
                   
                   
                 0.40 
               
               
                   
                 Rhenocure AP-5 
                 3.15 
                   
                   
                   
                   
                   
                 3.50 
               
               
                   
                 Rhenocure AP-7 
                   
                   
                   
                   
                 3.00 
               
               
                   
                 Rhenocure AP-3 
                   
                   
                   
                 3.85 
                   
                 3.85 
               
               
                   
                 Rhenocure ZADT/G 
                   
                   
                   
                 0.80 
                 0.80 
                 1.00 
               
               
                   
                 Rhenocure S/G 
                   
                   
                   
                 0.80 
                   
                 0.80 
               
               
                   
                 Altax 
                   
                 1.00 
                 1.10 
               
               
                   
                 Akroform Delta P.M. 
                   
                   
                 0.35 
               
               
                   
                 Sulfads 
                   
                   
                 0.50 
               
               
                   
                 Accelerator VS 
                   
                 2.70 
               
               
                   
                 Akrosperse IS-70 
                 1.00 
                 1.00 
                 1.00 
                   
                   
                   
                 1.05 
               
               
                   
                 Sulfur 
                   
                   
                   
                 0.40 
                 0.80 
                 0.40 
               
               
                   
                   
               
             
          
         
       
     
     In addition, individual batches of insulation formulations containing silica filler were prepared with NORDEL IP NDR-3725 (Example 1, Table 8 below), BUNA EP T 2370 (Example 2), and NORDEL 2722E (Comparative Example) as the secondary EPDM terpolymers having high ethylene contents. However, in these formulations it has been observed that there is an increased reactivity of the ethylidene norbornene monomers as used in Examples 1 and 2 (compared to the 1,4-hexadiene monomer of the Comparative Example A), and accordingly, SP 1055 (3 wt % bromine) was used in Examples 1 and 2 and SP 1056 (6 wt % bromine) was used in the Comparative Example A (Table 8) in equal quantities for comparison purposes. In addition, another formulation, RDL 5654 was also prepared in much the same way, but substituting NORDEL IP NDR-3722p for NORDEL IP NDR-2722E, and SP 1055 was used in place of SP 1056. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 7 
               
               
                   
               
               
                   
                 Ethylene 
                 Propylene 
                 Diene 
                   
               
               
                   
                 content 
                 content 
                 content 
                   
               
               
                 Polymer 
                 % 
                 % 
                 % type 
                 Viscosity 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 NORDEL IP NDR-3722 
                 71 
                 26.5 
                 2.5/ENB 
                 25 
               
               
                 BUNA EP T 2370 
                 71 
                 26 
                   3/ENB 
                 16 
               
               
                 NORDEL 2722E 
                 72 
                 22 
                 6.4/HD   
                 26 
               
               
                   
               
             
          
         
       
     
     The batches were each formulated in a laboratory scale Reliable Rubber &amp; Plastics Machinery Company Model R-260 internal mixer having a net chamber volume of 4260 cubic centimeters. A 3000 gram batch was prepared by a two-pass mix procedure. 
     In the first pass, the mixer speed was set at 40 rpm, and the primary and secondary polymer components, tackifier, and antidegradant were added to the mixing chamber in the concentrations set forth in Table 3 and masticated for one minute. Subsequently, the remaining ingredients were added (same concentrations as in Table 3), and the mixer speed was increased to 60 rpm. The batches were removed from the internal mixer after mixing for a total of approximately 7 minutes. The temperature at the time of removing the batch was 300° F. to 320° F. The master batch was sheeted out on a 6″×13″ Farrel Corporation laboratory two-roll mill and allowed to cool to room temperature. 
     In the second pass, the mixer speed was set to 40 rpm. In a sequential manner, half of the master batch was added to the mixer, then the curatives were added (same concentrations as set forth in Table 3), then the remaining half of the master batch was added to the mixer. After a total mix time of approximately 40 seconds, the final mix was removed from the mixer. The actual temperature at the time of removal was approximately 200° F. The material was sheeted out onto the laboratory mill and allowed to cool to room temperature prior to evaluating its rheological and physical properties. 
     The rheological properties of these several formulations are reported in Table 8. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 RHEOLOGICAL PROPERTIES (silica filler) 
               
             
          
           
               
                   
                 Example 1 
                 Example 2 
                   
                 Comparative 
               
               
                 Property 
                 [RDL5294] 
                 [RDL5331] 
                 RDL5654 
                 Example A 
               
               
                   
               
             
          
           
               
                 (1) Mooney viscosity (ML 1 + 4 at 
                 63.4 
                 61.0 
                 65.4 
                 68.8 
               
               
                 212° F.)(ASTM D 1646) 
               
               
                 (2) Mooney scorch (MS + 1 at 250° F., 
                 21.5 
                 18.1 
                 27.1 
                 11.8 
               
               
                 min.)(ASTM D 1646) 
               
               
                 (3) Oscillating disk rheometer (ODR 
                   
                   
                 — 
               
               
                 at 320° F., 5° arc)(ASTM D 2084) 
               
               
                 properties: 
               
             
          
           
               
                 (a) 
                 ML (minimum torque, in.-lb.) 
                 17.8 
                 16.4 
                 17.1 
                 21.4 
               
               
                   
                 (ASTM D 2084) 
               
               
                 (b) 
                 MH (maximum torque, at 2 hrs, 
                 91.0 
                 95.0 
                 86.8 
                 97.7 
               
               
                   
                 in.-lb.)(ASTM D 2084) 
               
               
                 (c) 
                 Ts2, (time to 2 point rise above 
                 2.3 
                 1.8 
                 2.4 
                 1.5 
               
               
                   
                 minimum viscosity, in min.) 
               
               
                   
                 (ASTM D 2084) 
               
               
                 (d) 
                 MC(90)(in.-lb.)(ASTM D 
                 83.7 
                 87.1 
                 79.8 
                 90.1 
               
               
                   
                 2084) 
               
               
                 (e) 
                 Tc (90)(min)(ASTM E 2084) 
                 74.0 
                 73.5 
                 77.1 
                 75.5 
               
               
                   
               
             
          
         
       
     
     The physical characteristics of these formulations are reported as follows in Table 9. 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 9 
               
             
             
               
                   
               
               
                 PHYSICAL PROPERTIES 
               
             
          
           
               
                   
                 Specification 
                 Example 1 
                 Example 2 
                   
                 Comparative 
               
               
                 Properties 
                 Requirement 
                 [RDL5294] 
                 [RDL5331] 
                 RDL 5654 
                 Example A 
               
               
                   
               
             
          
           
               
                 Shore A hardness 
                 69-79 
                 73.8 
                 74.2 
                 72.4 
                 71.8 
               
               
                 (ASTM D 2240) 
               
               
                 Ash content (%) 
                 20-26 
                 22.6 
                 22.4 
                 22.2 
                 22.7 
               
               
                 (ASTM D 297) 
               
               
                 Specific gravity 
                 1.04-1.07 
                 1.051 
                 1.058 
                 1.056 
                 1.054 
               
               
                 (ASTM D 792) 
               
               
                 Tensile strength, 
                 1450 min.  
                 2420 
                 2480 
                 2210 
                 2280 
               
               
                 perpendicular (psi; 
               
               
                 ASTM D 412) 
               
               
                 Elongation parallel (%; 
                 450 min 
                 703 
                 693 
                 643 
                 636 
               
               
                 ASTM D 412) 
               
               
                 100% modulus (psi) 
                 — 
                 347 
                 370 
                 377 
                 371 
               
               
                 Tear resistance (pli) 
                 170 min. 
                 233 
                 238 
                 230 
                 221 
               
               
                 (ASTM D 624) 
               
               
                 Specific heat (BTU 
                 — 
                 0.445 
                 0.442 
                 — 
                 0.443 
               
               
                 (lb.) −1 (° F.) −1    
               
               
                 (ASTM E 1269) 
               
               
                 Thermal conductivity 
                 — 
                 0.134 
                 0.133 
                 — 
                 0.129 
               
               
                 (BTU (ft) −1 (in.) −1 (° F.) −1   
               
               
                 (ASTM E 1225) 
               
               
                   
               
             
          
         
       
     
     Measurements were also made of the resulting ablation rates for these formulations. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 10 
               
             
             
               
                   
               
               
                 MATERIAL ABLATION RATE 
               
               
                 (MILS/SECOND) 
               
             
          
           
               
                   
                   
                   
                 Comparative 
               
               
                   
                 Example 1 
                 Example 2 
                 Example A 
               
               
                   
                   
               
             
          
           
               
                 Low Mach Region 
                 3.00 
                 3.13 
                 3.40 
               
               
                 (0.0028) 
               
               
                 Medium Mach Region 
                 7.34 
                 7.94 
                 7.60 
               
               
                 (0.0318-0.0386) 
               
               
                 High Mach Region 
                 19.60 
                 17.37 
                 20.11 
               
               
                 (0.0397-0.0634) 
               
               
                   
               
             
          
         
       
     
     The ablation tests for Table 10 were performed as follows. The tests were performed in a char motor, schematically illustrated in FIG.  2 . The samples for the three velocity regions of the motor (low, medium, and high Mach) were net molded using conventional compression molding techniques. The low Mach region had space for 15 specimens, while the medium and high Mach regions had space for 4 specimens. The thickness of each specimen was measured at several axial locations before and after firing. The char motor itself featured a propellant beaker filled with Thiokol Propulsion propellant TP-H1148 to a sufficient depth to provide for a 12-second burn with a tungsten nozzle radius of 0.24 inches. The actual action time and average operating pressure for the test motor were 11.7 seconds and 936 psi, respectively. 
     The cure characteristics and processability of the inventive Examples closely matched those of the Comparative Example A. The cure rates, as indicated by the 90 percent cure time tc(90), of Examples 1 and 2 were equivalent to that of the Comparative Example A. Similarly, the physical properties and ablative performance of the materials prepared in accordance with Examples 1 and 2 were substantially equivalent to those of the Comparative Example and were well within the specification requirements. Thus these results indicate that the new formulations have the capability of being substituted for the old standard to-be-discontinued insulations. 
     In addition, a comparison was made between DL1552A and RDL 5654 in a low mach test char motor using TP-H1148 propellant and a 30.8 second firing time at an average pressure of 881 psi. The following results indicate that RDL 5654 is a viable replacement for DLI 552A. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 10A 
               
             
             
               
                   
               
               
                 COMPARISON OF THE MATERIAL AFFECTED RATE (MAR) 
               
               
                 OF DL1552A AND RDL5654 IN THE LOW MACH CHAR MOTOR 
               
             
          
           
               
                   
                   
                 D-5 DL1552A 
                 RDL5654 
               
               
                   
                 Mach No. 
                 Average MAR 
                 Average MAR 
               
               
                   
                 Range 
                 (mils/sec.) 
                 (mils/sec.) 
               
               
                   
                   
               
             
          
           
               
                 Test motor 
                   
                 HPCAT-07 
                 MIR-05 
               
               
                 Low velocity test 
                 0.0027 
                 3.83 
                 3.86 
               
               
                 section 
               
               
                 Medium velocity test 
                 0.0027-0.0081 
                 3.79 
                 3.80 
               
               
                 section 
               
               
                 High velocity test 
                 0.0094-0.044  
                 5.36 
                 5.49 
               
               
                 section 
               
               
                   
               
             
          
         
       
     
     In the following TABLE 11 there are set forth examples of the new EPDM insulation formulations but now containing carbon fibers. 
     Batches of carbon fiber containing insulations generally may be formulated in a mixer via a two-pass mix procedure. In the first pass, the mixer speed may be set to approximately 40 rpm and the all of the components other than the curing agents, accelerators, and carbon fiber are added to the internal mixer. As the mixing proceeds, the temperature will increase up to about 300° F., or even higher. Suitable mixing times depend on the temperature and mixing speed, and are ascertainable to the skilled artisan without an undue amount of experimentation. 
     In the second pass, the mixer speed may be set to about 40 rpm., but this speed is dependent on the size of the mixer. In a sequential manner, half of the master batch was added to the mixer, then the curatives were added, then the remaining half of the master batch was added to the mixer. The second mixing step may be performed at a temperature rising to approximately 180° F. to 190° F. but below the temperature where the accelerator would become unduly activated. The material was sheeted out onto the laboratory mill and allowed to cool to room temperature. Then the material is dissolved in a suitable solvent, such as, by way of example, hydrocarbons such as hexane, heptane, and/or cyclohexane. The carbon fiber was then mixed with, for example, a sigma-blade mixer. The material is then sheeted out and the solvent allowed to evaporate at ambient atmosphere or in an oven. Throughout this process care must be taken that the frangible carbon fibers are not themselves fractured and broken up so as to become shortened and less effective as a result. 
     The shaping and curing of the inventive insulation may be performed in accordance with techniques known in the art. 
     The following Table 11 presents a number of examples of the novel EPDM formulations with carbon fibers. 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 11 
               
               
                   
               
               
                 EXAMPLES OF NEW EPDM FORMULATIONS WITR CARBON FIBER 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 INGREDIENT 
                 RDL5421 
                 RDL5420A 
                 RDL5377A 
                 RDL5444A 
                 RDL5443 
                 RDL5436 
                 RDL5408 
                 RDL5409 
               
               
                   
               
               
                 Keltan 4506 
               
               
                 Keltan 1446A 
               
               
                 Keltan 2308 
               
               
                 Nordel IP 4520 
                 40.0 
                 40.0 
                 45.0 
                 45.0 
                 45.0 
                   
                 80.0 
                 80.0 
               
               
                 Nordel IP 4640 
                 50.0 
                 50.0 
                 45.0 
                 45.0 
                 45.0 
                 80.0 
               
               
                 Hypalon 20 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
               
               
                 Neoprene FB 
               
               
                 Neoprene TW 
               
               
                 Neoprene GRT 
                   
                   
                   
                   
                   
                   
                 20.0 
                 20.0 
               
               
                 Trilene 67A 
                   
                   
                   
                   
                   
                 10.0 
               
               
                 Akrochem P-133 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
               
               
                 Agerite Resin D 
                   
                   
                   
                   
                   
                 2.0 
                 2.0 
                 2.0 
               
               
                 Agerite Stalite S 
                 2.0 
                 2.0 
                 2.0 
                 2.0 
                 2.0 
               
               
                 HiSil 233 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
               
             
          
           
               
                 VMC Carbon Fiber 
                 All formulations adjusted to have 26.75% VMC Carbon Fiber in finished product 
               
             
          
           
               
                 C. B. N330 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 Elastomag 170 
                   
                   
                   
                   
                   
                   
                 0.50 
                 0.50 
               
               
                 Zinc Oxide 
                 4.0 
                 5.0 
                 5.0 
                 5.0 
                 4.0 
                 4.0 
                 4.00 
                 4.00 
               
               
                 Butyl Zimate 
                 0.40 
                   
                 0.40 
                   
                   
                   
                   
                 0.50 
               
               
                 Rhenocure AP-5 
                 3.15 
                   
                 3.15 
                   
                   
                   
                   
                 3.40 
               
               
                 Rhenocure AP-7 
                   
                   
                   
                   
                   
                 3.00 
               
               
                 Rhenocure AP-3 
                   
                   
                   
                   
                   
                   
                 3.85 
               
               
                 Rhenocure ZADT/G 
                   
                   
                   
                   
                   
                 0.80 
                 1.00 
               
               
                 Rhenocure S/G 
                   
                   
                   
                   
                   
                   
                 0.80 
               
               
                 Altax 
                   
                 1.00 
                   
                 1.00 
                 1.10 
               
               
                 Akroform Delta P.M. 
                   
                   
                   
                   
                 0.35 
               
               
                 Sulfads 
                   
                   
                   
                   
                 0.50 
               
               
                 Accelerator VS 
                   
                 2.70 
                   
                 2.70 
               
               
                 Akrosperse IS-70 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
               
               
                 Sulfur 
                   
                   
                   
                   
                   
                 0.80 
                 0.40 
                 0.50 
               
               
                   
               
             
          
           
               
                   
                 Ingredient 
                 RDL5445 
                 RDL5410 
                 RDL5375 
                 RDL5395 
                 RDL5394 
                 RDL5435 
                 RDL5434 
                 RDL5376A 
               
               
                   
                   
               
               
                   
                 Keltan 4506 
                   
                 70.0 
                 73.0 
                 55.0 
                 55.0 
                   
                   
                   
               
               
                   
                 Keltan 1446A 
                   
                 20.0 
                 17.0 
               
               
                   
                 Keltan 2308 
                   
                   
                   
                 35.0 
                 35.0 
               
               
                   
                 Nordel IP 4520 
                 80.0 
                   
                   
                   
                   
                   
                   
                 80.0 
               
               
                   
                 Nordel IP 4640 
                   
                   
                   
                   
                   
                 80.0 
                 80.0 
               
               
                   
                 Hypalon 20 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
               
               
                   
                 Neoprene FB 
                   
                   
                   
                   
                   
                 20.0 
                 20.0 
               
               
                   
                 Neoprene TW 
                   
                   
                   
                   
                   
                   
                   
                 20.0 
               
               
                   
                 Neoprene GRT 
               
               
                   
                 Trilene 67A 
                 10.0 
               
               
                   
                 Akrochem P-133 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
                 5.0 
                   
                   
                 5.0 
               
               
                   
                 Agerite Resin D 
                 2.0 
                   
                   
                   
                   
                 2.0 
                 2.0 
                 2.0 
               
               
                   
                 Agerite Stalite S 
                   
                 2.0 
                 2.0 
                 2.0 
                 2.0 
               
               
                   
                 HiSil 233 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
                 3 
               
             
          
           
               
                   
                 VMC Carbon Fiber 
                 All formulations adjusted to have 26.75% VMC Carbon Fiber in finished product 
               
             
          
           
               
                   
                 C. B. N330 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                   
               
               
                   
                 Elastomag 170 
                   
                   
                   
                   
                   
                   
                   
                 0.5 
               
               
                   
                 Zinc Oxide 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 5.0 
               
               
                   
                 Butyl Zimate 
                 0.15 
                 0.50 
                   
                   
                   
                   
                   
                 0.50 
               
               
                   
                 Rhenocure AP-5 
                 4.45 
                 3.50 
                   
                   
                   
                   
                   
                 3.50 
               
               
                   
                 Rhenocure AP-7 
               
               
                   
                 Rhenocure AP-3 
                   
                   
                   
                   
                   
                 2.90 
               
               
                   
                 Rhenocure ZADT/G 
                   
                   
                   
                   
                   
                 0.80 
               
               
                   
                 Rhenocure S/G 
                   
                   
                   
                   
                   
                 0.60 
               
               
                   
                 Altax 
                   
                   
                 1.10 
                 1.10 
                 1.20 
                   
                 1.10 
               
               
                   
                 Akroform Delta P.M. 
                   
                   
                   
                   
                 0.45 
                   
                 0.20 
               
               
                   
                 Sulfads 
                   
                   
                   
                   
                 0.50 
               
               
                   
                 Accelerator VS 
                   
                   
                 2.70 
                 2.70 
               
               
                   
                 Akrosperse IS-70 
                 1.34 
                 1.10 
                 1.20 
                 1.20 
                 1.40 
                   
                   
                 1.00 
               
               
                   
                 Sulfur 
                   
                   
                   
                   
                   
                 0.35 
                 0.45 
               
               
                   
                   
               
             
          
         
       
     
     Silica Powder Filled Insulation Properties 
     TABLE 12 reports rheological properties measured for the silica powder thermal insulation formulations that were set forth in TABLE 6. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 12 
               
             
             
               
                   
               
               
                 RHEOLOGICAL PROPERTIES 
               
               
                 (silica powder) 
               
             
          
           
               
                   
                   
                 Oscillating disk rheometer 
                   
               
               
                   
                   
                 (ODR at 320° F., 5° arc) 
               
               
                   
                 Mooney 
                 (ASTM D 2084) 
               
             
          
           
               
                   
                 viscosity 
                   
                 MH 
                 ts2, 
                   
               
               
                   
                 (ML 1+4 
                 ML 
                 maximum 
                 (time to 2 
                   
               
               
                 Silica-Filled 
                 at 212° F. 
                 (minimum 
                 torque, 
                 point rise 
                 Tc 
               
               
                 EPDM 
                 (ASTM 
                 torque, 
                 at 1 hrs, 
                 above ML, 
                 (90) 
               
               
                 Formulation 
                 D 1646) 
                 in.-lb.) 
                 in.-lb.) 
                 in min.) 
                 (min) 
               
               
                   
               
             
          
           
               
                 RDL 5338 
                 72.0 
                 17.7 
                 93.9 
                 6.0 
                 43.5 
               
               
                 RDL 5342 
                 78.5 
                 21.3 
                 97.8 
                 7.0 
                 45.0 
               
               
                 RDL 5343 
                 78.8 
                 19.9 
                 98.0 
                 4.3 
                 44.5 
               
               
                 RDL 5347 
                 84.0 
                 21.7 
                 94.5 
                 3.4 
                 38.0 
               
               
                 RDL 5363 
                 83.0 
                 22.9 
                 87.2 
                 3.3 
                 44.2 
               
               
                 RDL 5255 
                 85.7 
                 19.4 
                 103.2 
                 3.6 
                 28.5 
               
               
                 RDL 5335 
                 87.7 
                 23.4 
                 93.4 
                 2.7 
                 38.5 
               
               
                 RDL 5201 
                 73.0 
                 16.4 
                 89.0 
                 6.2 
                 31.5 
               
               
                 RDL 5220 
                 71.2 
                 16.0 
                 110.0 
                 5.9 
                 40.0 
               
               
                 RDL 5370 
                 80.0 
                 20.3 
                 104.6 
                 5.6 
                 32.0 
               
               
                 RDL 5380 
                 80.3 
                 21.0 
                 107.4 
                 7.3 
                 56.0 
               
               
                 RDL 5381 
                 79.6 
                 21.0 
                 104.0 
                 4.8 
                 36.0 
               
               
                 RDL 5194 
                 62.0 
                 13.4 
                 90.9 
                 8.7 
                 44.0 
               
               
                 RDL 5222 
                 61.9 
                 13.5 
                 92.8 
                 6.3 
                 45.6 
               
               
                 RDL 5273A 
                 64.5 
                 14.7 
                 97.1 
                 3.8 
                 42.0 
               
               
                 RDL 5298 
                 51.0 
                 11.0 
                 91.0 
                 7.1 
                 49.0 
               
               
                 RDL 5277 
                 72.4 
                 18.9 
                 98.5 
                 1.9 
                 42.6 
               
               
                 RDL 5279 
                 75.0 
                 17.3 
                 93.0 
                 2.7 
                 18.8 
               
               
                 RDL 5319 
                 87.8 
                 19.9 
                 97.0 
                 6.3 
                 43.0 
               
               
                 RDL 5320A 
                 86.5 
                 20.7 
                 103.0 
                 4.0 
                 41.6 
               
               
                 RDL 5350 
                 83.0 
                 22.0 
                 103.0 
                 6.8 
                 46.1 
               
               
                 RDL 5351A 
                 84.6 
                 19.8 
                 105.6 
                 3.5 
                 37.0 
               
               
                 RDL 5367 
                 86.0 
                 22.3 
                 96.7 
                 3.2 
                 43.3 
               
               
                 RDL 5185 
                 79.5 
                 18.7 
                 90.0 
                 8.4 
                 40.9 
               
               
                 RDL 5186 
                 80.6 
                 19.3 
                 95.5 
                 4.1 
                 43.0 
               
               
                 RDL 5205 
                 79.9 
                 19.4 
                 94.0 
                 8.0 
                 41.2 
               
               
                 RDL 5276 
                 81.6 
                 18.5 
                 96.7 
                 6.2 
                 42.5 
               
               
                   
               
             
          
         
       
     
     TABLE 13 reports various physical properties measured for the silica powder thermal insulation formulations that were set forth in TABLE 6. 
     
       
         
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 13 
               
             
             
               
                   
               
               
                 PHYSICAL PROPERTIES 
               
             
          
           
               
                 Silica-Filled 
                   
                   
                   
                   
                   
                   
                   
               
               
                 EPDM 
               
               
                 Formulation 
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
                 G 
               
               
                   
               
               
                 RDL 5338 
                 2280 
                 646 
                 2260 
                 658 
                 220 
                 62.0 
                 1.06 
               
               
                 RDL 5342 
                 1910 
                 588 
                 1790 
                 582 
                 206 
                 63.4 
                 1.06 
               
               
                 RDL 5343 
                 2330 
                 655 
                 2040 
                 619 
                 221 
                 63.2 
                 1.06 
               
               
                 RDL 5347 
                 2100 
                 621 
                 2060 
                 630 
                 271 
                 68.6 
                 1.06 
               
               
                 RDL 5363 
                 2920 
                 610 
                 2820 
                 608 
                 270 
                 72.0 
                 1.06 
               
               
                 RDL 5255 
                 2430 
                 703 
                 2330 
                 695 
                 223 
                 69.4 
                 1.10 
               
               
                 RDL 5335 
                 2560 
                 725 
                 2600 
                 739 
                 232 
                 65.2 
                 1.10 
               
               
                 RDL 5201 
                 2150 
                 772 
                 2220 
                 779 
                 190 
                 70.2 
                 1.10 
               
               
                 RDL 5220 
                 2170 
                 634 
                 2020 
                 620 
                 194 
                 70.2 
                 1.10 
               
               
                 RDL 5370 
                 2550 
                 700 
                 2340 
                 688 
                 201 
                 70.4 
                 1.10 
               
               
                 RDL 5380 
                 2610 
                 688 
                 2300 
                 663 
                 206 
                 69.4 
                 1.11 
               
               
                 RDL 5381 
                 2420 
                 700 
                 2470 
                 701 
                 207 
                 69.0 
                 1.11 
               
               
                 RDL 5194 
                 1920 
                 734 
                 1920 
                 748 
                 201 
                 71.8 
                 1.05 
               
               
                 RDL 5222 
                 2100 
                 703 
                 1960 
                 653 
                 218 
                 71.2 
                 1.05 
               
               
                 RDL 5273A 
                 1420 
                 612 
                 1430 
                 613 
                 241 
                 70.4 
                 1.06 
               
               
                 RDL 5298 
                 1910 
                 592 
                 1870 
                 586 
                 223 
                 71.6 
                 1.06 
               
               
                 RDL 5277 
                 2010 
                 614 
                 2190 
                 632 
                 181 
                 66.4 
                 1.05 
               
               
                 RDL 5279 
                 2390 
                 672 
                 2370 
                 687 
                 199 
                 64.8 
                 1.05 
               
               
                 RDL 5319 
                 2440 
                 659 
                 2270 
                 647 
                 205 
                 71.2 
                 1.05 
               
               
                 RDL 5320A 
                 2250 
                 657 
                 2220 
                 653 
                 224 
                 71.6 
                 1.06 
               
               
                 RDL 5350 
                 2350 
                 688 
                 2420 
                 707 
                 233 
                 64.2 
                 1.06 
               
               
                 RDL 5351A 
                 2270 
                 681 
                 2250 
                 699 
                 226 
                 65.2 
                 1.06 
               
               
                 RDL 5367 
                 2440 
                 621 
                 2430 
                 625 
                 238 
                 70.4 
                 1.06 
               
               
                 RDL 5185 
                 2310 
                 776 
                 2230 
                 771 
                 208 
                 71.4 
                 1.06 
               
               
                 RDL 5186 
                 2390 
                 725 
                 2290 
                 718 
                 221 
                 71.6 
                 1.06 
               
               
                 RDL 5205 
                 1990 
                 729 
                 2120 
                 773 
                 207 
                 71.6 
                 1.06 
               
               
                 RDL 5276 
                 2270 
                 653 
                 2210 
                 656 
                 223 
                 71.2 
                 1.06 
               
               
                   
               
               
                 Key:  
               
               
                 A = Tensile strength, parallel (psi)(ASTM D 412)  
               
               
                 B = Elongation Parallel (%)(ASTM D 412)  
               
               
                 C = Tensile Strength Perpendicular (ASTM D 412)  
               
               
                 D = Elongation Perpendicular (ASTM D 412)  
               
               
                 E = Tear Strength (ASTM D 412)  
               
               
                 F = Shore A hardness (ASTM D 2240)  
               
               
                 G =Specific gravity (ASTM D 792)  
               
             
          
         
       
     
     Carbon-Fiber Containing Insulation Formulation Properties 
     Next, Table 14 lists the rheological properties measured according to the indicated tests for the carbon fiber-containing insulation formulations set forth in TABLE 11. 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 14 
               
             
             
               
                   
               
               
                 RHEOLOGICAL PROPERTIES 
               
             
          
           
               
                   
                 Oscillating Disk Rheometer 
               
               
                   
                 (ODR at 300° F., 5° arc) 
               
               
                   
                 (ASTM D 2084) 
               
             
          
           
               
                   
                   
                   
                   
                 ts2, 
                   
               
               
                   
                 Mooney 
                   
                   
                 (time to 
               
               
                   
                 viscosity 
                   
                   
                 a 2 point 
               
               
                 Carbon- 
                 (ML 1 + 4 
                 ML 
                 MH 
                 rise 
                 Tc 
               
               
                 Fiber 
                 at 212° F.) 
                 (minimum 
                 (maximum 
                 above 
                 (90% 
               
               
                 EPDM 
                 (ASTM D 
                 torque, 
                 torque, at 1 
                 ML; in 
                 cure) 
               
               
                 Formulation 
                 1646) 
                 in.-lb.) 
                 hr, in.-lb.) 
                 min.) 
                 (min) 
               
               
                   
               
             
          
           
               
                 RDL 5421 
                 72.4 
                 23.3 
                 111 
                 3.5 
                 30.2 
               
               
                 RDL 5420A 
                 70.0 
                 21.2 
                 119 
                 2.9 
                 37.0 
               
               
                 RDL 5377A 
                 68.0 
                 18.8 
                 102 
                 2.8 
                 36.5 
               
               
                 RDL 5444A 
                 67.4 
                 21.0 
                 110 
                 3.2 
                 28.0 
               
               
                 RDL 5443 
                 74.5 
                 25.7 
                 101 
                 1.6 
                 33.5 
               
               
                 RDL 5436 
                 80.0 
                 25.8 
                 98.2 
                 2.6 
                 32.0 
               
               
                 RDL 5408 
                 83.0 
                 29.2 
                 95.5 
                 2.5 
                 16.5 
               
               
                 RDL 5409 
                 83.8 
                 25.8 
                 99.0 
                 3.5 
                 25.5 
               
               
                 RDL 5445 
                 56.0 
                 15.8 
                 82.0 
                 3.4 
                 39.2 
               
               
                 RDL 5410 
                 81.0 
                 18.6 
                 103 
                 4.8 
                 34.5 
               
               
                 RDL 5375 
                 55.0 
                 21.0 
                 100 
                 2.5 
                 31.7 
               
               
                 RDL 5395 
                 64.7 
                 29.2 
                 87.4 
                 3.2 
                 35.0 
               
               
                 RDL 5394 
                 67.0 
                 25.1 
                 89.5 
                 1.8 
                 36.0 
               
               
                 RDL 5410 
                 81.0 
                 18.0 
                 103 
                 4.8 
                 34.5 
               
               
                 RDL 5434 
                 43.7 
                 12.1 
                 136 
                 1.9 
                 18.8 
               
               
                 RDL 5435 
                 39.0 
                 9.1 
                 118 
                 2.3 
                 19.0 
               
               
                   
               
             
          
         
       
     
     Table 15 reports the physical properties measured for the carbon fiber-containing insulation formulations set forth in TABLE 11. 
     
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 15 
               
             
             
               
                   
               
               
                 PHYSICAL PROPERTIES 
               
             
          
           
               
                 Carbon-Fiber 
                   
                   
                   
                   
                   
                   
               
               
                 EPDM Form. 
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
               
               
                   
               
             
          
           
               
                 RDL 5421 
                 1750 
                 3.34 
                 820 
                 4.59 
                 84.4 
                 1.097 
               
               
                 RDL 5420A 
                 1600 
                 3.12 
                 871 
                 4.60 
                 84.2 
                 1.106 
               
               
                 RDL 5377A 
                 1540 
                 3.11 
                 814 
                 4.03 
                 82.6 
                 1.072 
               
               
                 RDL 5444A 
                 2030 
                 5.01 
                 884 
                 6.30 
                 84.2 
                 1.097 
               
               
                 RDL 5443 
                 2070 
                 5.37 
                 799 
                 7.21 
                 83.2 
                 1.090 
               
               
                 RDL 5436 
                 1500 
                 2.48 
                 721 
                 4.05 
                 84.0 
                 1.098 
               
               
                 RDL 5408 
                 1060 
                 3.77 
                 525 
                 5.61 
                 81.2 
                 1.131 
               
               
                 RDL 5409 
                 1112 
                 2.95 
                 668 
                 3.35 
                 83.4 
                 1.142 
               
               
                 RDL 5445 
                 1160 
                 3.58 
                 725 
                 4.71 
                 84.4 
                 1.096 
               
               
                 RDL 5410 
                 1500 
                 2.88 
                 719 
                 3.85 
                 83.8 
                 1.063 
               
               
                 RDL 5375 
                 2010 
                 4.38 
                 881 
                 6.85 
                 80.6 
                 l.076 
               
               
                 RDL 5395 
                 2650 
                 4.55 
                 1090 
                 4.98 
                 86.1 
                 1.078 
               
               
                 RDL 5394 
                 2218 
                 3.80 
                 982 
                 4.84 
                 87.2 
                 1.088 
               
               
                 RDL 5435 
                 1690 
                 4.17 
                 905 
                 6.03 
                 83.4 
                 1.127 
               
               
                 RDL 5434 
                 1470 
                 4.41 
                 786 
                 5.82 
                 83.6 
                 1.126 
               
               
                 RDL 5410 
                 1500 
                 2.88 
                 719 
                 3.85 
                 83.8 
                 1.063 
               
               
                 RDL 5435 
                 1690 
                 4.17 
                 905 
                 6.03 
                 83.4 
                 1.127 
               
               
                 RDL 5434 
                 1470 
                 4.41 
                 786 
                 5.82 
                 83.6 
                 1.126 
               
               
                   
               
               
                 Key:  
               
               
                 A = Tensile strength, parallel (psi) (ASTM D 412)  
               
               
                 B = Elongation Parallel (%) (ASTM D 412)  
               
               
                 C = Tensile Strength Perpendicular (ASTM D 412)  
               
               
                 D = Elongation Perpendicular (ASTM D 412)  
               
               
                 E = Shore A hardness (ASTM D 2240)  
               
               
                 F = Specific gravity (ASTM D 792)  
               
             
          
         
       
     
     The following TABLE 16 shows the results of ablation tests with the silica powder-containing formulations of Tables 6, 12 and 13. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 16 
               
             
             
               
                   
               
               
                 MATERIAL ABLATION RATE 
               
               
                 (MILS/SECOND) 
               
             
          
           
               
                   
                   
                 Low Velocity, 
               
               
                   
                 Silica powder Filled 
                 0.003 Mach 
               
               
                   
                   
               
               
                   
                 RDL 5338 
                 3.65 
               
               
                   
                 RDL 5343 
                 3.14 
               
               
                   
                 RDL 5347 
                 2.31 
               
               
                   
                 RDL 5363 
                 2.82 
               
               
                   
                 RDL 5255 
                 2.76 
               
               
                   
                 RDL 5335 
                 2.42 
               
               
                   
                 RDL 5220 
                 3.66 
               
               
                   
                 RDL 5370 
                 3.44 
               
               
                   
                 RDL 5380 
                 3.24 
               
               
                   
                 RDL 5298 
                 3.36 
               
               
                   
                 RDL 5319 
                 3.23 
               
               
                   
                 RDL 5320 
                 2.81 
               
               
                   
                 RDL 5350 
                 3.38 
               
               
                   
                 RDL 5351 
                 3.35 
               
               
                   
                 RDL 5367 
                 3.31 
               
               
                   
                 RDL 5186 
                 2.34 
               
               
                   
                   
               
             
          
         
       
     
     The ablation tests were performed as follows. The tests were performed in a char motor, schematically illustrated in FIG.  2 . The samples for the three velocity regions of the motor (low, medium, and high Mach) were neat molded using conventional compression molding techniques. The low Mach region had space for 15 specimens, while the medium and high Mach regions had space for 4 specimens. The thickness of each specimen was measured at several axial locations before and after firing. The char motor itself featured a propellant beaker filled with Thiokol Propulsion propellant TP-H1148 to a sufficient depth to provide for a 12-second burn with a tungsten nozzle radius of 0.24 inches. The actual action time and average operating pressure for the test motor were 12.1 seconds and 860 psi, respectively. 
     The following TABLE 17 shows the results of ablation tests with the carbon fiber-containing formulations of Tables 11, 14 and 15. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 17 
               
             
             
               
                   
               
               
                 MATERIAL ABLATION RATE 
               
               
                 (MILS/SECOND) 
               
             
          
           
               
                   
                   
                 Medium Velocity, 
                 High Velocity, 
               
               
                 Carbon fiber 
                 Low Velocity, 
                 Avg. 
                 Avg. 
               
               
                 EPDM 
                 0.003 Mach 
                 0.03-0.09 Mach 
                 0.01-0.15 Mach 
               
               
                   
               
               
                 RDL 5421 
                 3.38 
                 11.4 
                 18.7 
               
               
                 RDL 5420 
                 2.87 
                 12.2 
                 19.2 
               
               
                 RDL 5377 
                 3.86 
                 11.5 
                 17.6 
               
               
                 RDL 5444 
                 3.29 
                 10.7 
                 18.4 
               
               
                 RDL 5443 
                 3.22 
                 12.5 
                 19.9 
               
               
                 RDL 5436 
                 2.63 
                 11.0 
                 15.3 
               
               
                 RDL 5408 
                 3.91 
                 11.2 
                 16.5 
               
               
                 RDL 5409 
                 4.12 
                 10.6 
                 15.5 
               
               
                 RDL 5410 
                 3.55 
                 10.9 
                 19.9 
               
               
                 RDL 5375 
                 2.97 
                 12.3 
                 16.0 
               
               
                 RDL 5395 
                 3.00 
                 11.7 
                 20.8 
               
               
                 RDL 5394 
                 3.05 
                 11.7 
                 20.2 
               
               
                 RDL 5435 
                 3.90 
                 11.4 
                 15.1 
               
               
                 RDL 5434 
                 3.90 
                 11.3 
                 15.3 
               
               
                 RDL 5376 
                 4.27 
                 12.9 
                 14.7 
               
               
                 RDL 5445 
                 3.45 
                 11.3 
                 18.3 
               
               
                   
               
             
          
         
       
     
     The ablation tests were also performed, as follows. The tests were performed in a char motor, schematically illustrated in FIG.  2 . The samples for the low velocity region of the motor was molded using conventional compression molding techniques. The low Mach region had space for 15 specimens. The thickness of each specimen was measured at several axial locations before and after firing. The char motor itself featured a propellant beaker filled with Thiokol Propulsion propellant TP-H1148 to a sufficient depth to provide for a 12-second burn with a tungsten nozzle radius of 0.24 inches. The actual action time and average operating pressure for the test motor were 12.1 seconds and 860 psi, respectively. 
     From the characteristics measured in these tables it can be seen that a special combination of properties is required for a suitable insulation. And it is important to the consideration of this invention that the formulations are effective as to both of the commonly used solid additives silica powder and carbon fibers. 
     With reference to the results set forth in the foregoing tables it is presently considered in Table 13 (silica filled EPDM) that the minimum acceptable values for tensile strength (parallel and perpendicular, values A and C) should be at least about 1600, and are preferably close to equal (within about plus or minus 10%). The elongation (parallel and perpendicular, Table 13) should be in the range of about 550-850. For tear strength, the value of about 170 is presently seen as a minimum characteristic. Similarly, an ODR-measured maximum torque MH (Table 12) for the silica powder filled insulations should be at least about 85 in-lb. and at most about 120 in-lb., preferably at most about 115 in-lb. is currently thought to be appropriate. The ODR torque ML has a useful lower limit of about 5 in-lb., preferably about 10. The scorch test Ts result (Tables 12 and 14) should be at least 1.5. For silica filled insulations, the tear strength (Table 13) should be at least about 170. For carbon fiber containing insulations, the elongation should exhibit a minimum of at least about 2%, preferably at least about 2.5%, especially for measurement B in Table 15. Also, for the carbon fiber insulations (Table 14) the Mooney viscosity ML should be below about 90 Mooney units. 
     Considering the combined properties of the individual insulations noted in the above Tables, the silica-filled insulation 5273A is not presently preferred nor are the carbon-fiber containing insulations 5408, 5409, 5434 and 5445. 
     In addition, formulations were also made with using aramid fibers as the filler material. An exemplary EPDM terpolymer for use with Kevlar fibers and comprising ENB as its diene component is NORDEL IP NDR-4640 (available from DuPont Dow Elastomers), may be substituted into the R196 for the NORDEL 1040 without requiring significant modifications to the R196 formulation. Generally, the one significant modification that is required with the use of aramid fibers involves a reduction in the amount of the curing agent, e.g., peroxide, again to offset the increased reactivity (relative to HD) of the alkylidene norbornenes. Furthermore, NORDEL IP NDR-4640 is not presently foreseen as being susceptible to obsolescence issues. 
     Thus, in accordance with a further embodiment of this invention utilizing aramid fibers, the inventive rocket motor insulation formulation comprises, as a polymeric base, an EPDM/polyisoprene blend in which the diene component of the EPDM is based on at least one alkylidene norbornene, such as ethylidene norbornene (ENB), in effect in place of and without the above-described primary EPDM. The alkylidene norbornene content of such an EPDM may be from about 2-10 wt %. The selected EPDM terpolymer should be substitutable into the R196 thermal insulation formulation (Table 4) without requiring significant modification of the formulation. In accordance with a preferred embodiment, the EPDM terpolymer is NORDEL IP NDR-4640, which includes ENB as its diene monomer, is available from DuPont Dow Elastomers, and is manufactured in a relatively large capacity. 
     An exemplary aramid fiber formulation is set forth in TABLE 18: 
     
       
         
               
               
             
           
               
                 TABLE 18 
               
               
                   
               
               
                   
                 Parts by 
               
               
                 Ingredient 
                 Weight 
               
               
                   
               
             
             
               
                 EPDM terpolymer with ENB diene monomer component 
                 79.5-80.5 
               
               
                 Polyisoprene 
                 19.5-20.5 
               
               
                 Antioxidant 
                 0.95-1.05 
               
               
                 Halogen-containing flame retardant 
                 39.5-40.5 
               
               
                 Metal oxide flame retardant 
                 19.5-20.5 
               
               
                 KEVLAR fiber (aramid staple fiber) 
                 19.5-20.5 
               
               
                 Curing agent 
                 1.45-1.55 
               
               
                   
               
             
          
         
       
     
     In a more preferred embodiment, the polyisoprene, antioxidant, flame retardants, and aramid, e.g. KEVLAR, fibers are the same as those set forth in Table 4 above and are present in the concentrations specified in Table 4. The metal oxide may be present in fine powdery form so as to also serve as a filler. Varox DBPH-50 is also a suitable peroxy curing agent, although the substitution of ethylidene norbornene for 1,4-hexadiene requires a reduction in curing agent concentration to offset the increased reactivity of ethylidene norbornene. By providing the reformulated thermal insulation formulation with a peroxide concentration in a range of from about 1 to about 2.5 phr, more preferably about 1.5 phr, curing effect is achieved similar to the properties of R196. 
     In general, the said EPDM/polyisoprene combination may be used with about 60-90 wt % of the norbornene EPDM and about 40-10 wt % polyisoprene, again with suitable additives being present in functionally desired amounts. 
     Suitable additives that may be added as functionally required or as desired include one or more of the following, in various combinations: fillers, antidegradants, curing agents, plasticizers, processing aids, and pigments, bonding agents, fibers, and flame retardants. Two classes of curing systems that may be used are sulfur based curing agents in combination with organic accelerators, and peroxide curing agents. 
     The shaping and curing of the such aramid inventive insulations may be performed in accordance with techniques known in the art. 
     Example of Aramid Fiber Insulations 
     Individual batches of insulation formulations were prepared USING NORDEL IP NDR-4640 (Example, in Table 20) and NORDEL IP NDR-1040 (Comparative Example B). 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 19 
               
               
                   
               
               
                   
                 Ethylene 
                 Propylene 
                 Diene 
                   
               
               
                 Polymer 
                 content 
                 content 
                 content/type 
                 Viscosity 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 NORDEL IP 
                 55 
                 40 
                 5/ENB 
                 40 
               
               
                 NDR-4640 
               
               
                 NORDEL 
                 55 
                 41 
                 4/HD 
                 40 
               
               
                 1040 
               
               
                   
               
             
          
         
       
     
     The batches were each formulated in a laboratory scale Reliable Rubber &amp; Plastics Machinery Company Model R-260 internal mixer having a net chamber volume of 4260 cubic centimeters. A 3000 gram batch was prepared by a two-pass mix procedure. 
     In the first pass, the mixer speed was set at 40 rpm, and 80 parts by weight of the corresponding EPDM component set forth in Table 3, 20 parts by weight of NATSYN 2200 polyisoprene, and 1.0 parts by weight of Wingstay S were added to the mixing chamber and masticated for one minute. Subsequently, 40 parts by weight of Dechlorane Plus 515, 20 parts by weight of Sb 2 O 3 , and 20 parts by weight of ¼ inch KEVLAR aramid fibers were added, and the mixer speed was increased to 60 rpm. The batches were removed from the internal mixer after mixing for a total of approximately 7 minutes. The temperature at the time of removing the batch was 300° F. to 320° F. The master batch was sheeted out on a 6″×13″ Farrel Corporation laboratory two-roll mill and allowed to cool to room temperature. 
     For the Example and Comparative Example B, the fibers were dispersed in a two-roll mill to reduce agglomerations of fibers. The dispersion was accomplished by tightening the nip (separation between the two rolls) to 0.030 inches on the laboratory two-roll mill and passing the rubber through the nip a minimum of six times. This dispersion step was performed after the first pass but before the second pass. The rubber was then allowed to cool before the second pass. 
     In the second pass, the mixer speed was set to 40 rpm. In a sequential manner, half of the master batch was added to the mixer, then the curatives were added at a peroxide level of 1.5 phr, then the remaining half of the master batch was added to the mixer. After a total mix time of approximately 40 seconds, the final mix was removed from the mixer. The actual temperature at the time of removal was approximately 200° F. The material was sheeted out onto the laboratory mill and allowed to cool to room temperature prior to evaluating its rheological and physical properties. 
     Table 20 gives the measured rheological properties of these examples. 
     
       
         
               
             
               
               
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 20 
               
             
             
               
                   
               
               
                 RHEOLOGICAL PROPERTIES 
               
             
          
           
               
                   
                   
                 Comparative 
               
               
                 Property 
                 Example 
                 Example B 
               
               
                   
               
             
          
           
               
                 (1) Mooney viscosity (ML 1 + 4 at 
                 58.2 
                 51.3 
               
               
                 212° F.)(ASTM D 1646) 
               
               
                 (2) Mooney scorch (MS + 1 at 270° F., 
                 52.0 
                 27.8 
               
               
                 min.)(ASTM D 1646) 
               
               
                 (3) Oscillating disk rheometer (ODR at 
               
               
                 320° F., 5° arc) (ASTM D 2084) 
               
               
                 properties: 
               
             
          
           
               
                 (a) 
                 ML (minimum torque, in.-lb.) 
                 11.3 
                 13.3 
               
               
                   
                 (ASTM D 2084) 
               
               
                 (b) 
                 MH (maximum torque, at 2 hrs, 
                 61.5 
                 55.0 
               
               
                   
                 in.-lb.)(ASTM D 2084) 
               
               
                 (c) 
                 Ts2, (time to 2 point rise above 
                 4.3 
                 3.3 
               
               
                   
                 minimum viscosity, in min.) 
               
               
                   
                 (ASTM 2084) 
               
               
                 (d) 
                 MC(90)(in.-lb.)(ASTM 2084) 
                 56.4 
                 50.8 
               
               
                 (e) 
                 Tc(90)(min)(ASTM E 2084) 
                 65.5 
                 63.0 
               
               
                   
               
             
          
         
       
     
     Table 21 reports the physical properties of these aramid fiber examples. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 21 
               
             
             
               
                   
               
               
                 PHYSICAL PROPERTIES 
               
             
          
           
               
                   
                 Specification 
                   
                 Comparative 
               
               
                 Properties 
                 Requirement 
                 Example 
                 Example B 
               
               
                   
               
             
          
           
               
                 Density (lbs/in 3 )(ASTM D 
                 0.040 
                 min 
                 0.0422 
                 0.0421 
               
               
                 792) 
               
             
          
           
               
                 Shore A hardness (ASTM D 
                 70-85 
                 75.8 
                 74.4 
               
               
                 2240) 
               
             
          
           
               
                 Tensile strength, parallel (psi) 
                 700 
                 min 
                 1085 
                 1050 
               
               
                 (ASTM D 412) 
               
               
                 Elongation parallel (%) 
                 10 
                 min 
                 27.3 
                 24.6 
               
               
                 (ASTM D 412) 
               
             
          
           
               
                 Tensile strength, perpendicular 
                 — 
                 461 
                 367 
               
               
                 (psi)(ASTM D 412) 
               
               
                 Elongation, perpendicular (%) 
                 — 
                 109 
                 126 
               
               
                   
               
             
          
         
       
     
     Table 22 reports the results from a test to measure the ablation rates for these aramid fiber examples. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 22 
               
             
             
               
                   
               
               
                 MATERIAL ABLATION RATE (MILS/SECOND) 
               
             
          
           
               
                   
                   
                 Comparative 
               
               
                   
                 Example 
                 Example B 
               
               
                   
                   
               
             
          
           
               
                 Low Mach Region (0.0028) 
                 3.58 
                 3.43 
               
               
                 Medium Mach Region (0.039-0.0970) 
                 10.55 
                 10.83 
               
               
                 High Mach Region (0.109-0.140) 
                 16.59 
                 21.99 
               
               
                   
               
             
          
         
       
     
     The ablation tests were performed as follows. The tests were performed in a char motor, schematically illustrated in FIG.  2 . The samples for the three velocity regions of the motor (low, medium, and high Mach) were net molded using conventional compression molding techniques. The low Mach region had space for 15 specimens, while the medium and high Mach regions had space for 4 specimens. The thickness of each specimen was measured at several axial locations before and after firing. The char motor itself featured a propellant beaker filled with Thiokol Propulsion propellant TP-H1148 to a sufficient depth to provide for a 12-second burn with a tungsten nozzle radius of 0.24 inches. The actual action time and average operating pressure for the test motor were 12.0 seconds and 842 psi, respectively. 
     Although the Mooney scorch time of the Example was somewhat longer than that of the Comparative Example (R196), at the cure temperature of 320° F., the cure rates, as indicated by the 90 percent cure time tc(90), of the two materials were equivalent. Similarly, the physical properties of the materials prepared in accordance with the Example and Comparative Example B were substantially equivalent and well within the specification requirements. Additionally, the ablative performance of the material prepared in accordance with the inventive Example was equivalent or better than the ablative performance of the Comparative Example B (R196). 
     In the course of experimentation leading to this invention, a number of other candidate elastomeric formulations were tried in the hopes that the path to a new acceptable insulation would not be overly difficult. In fact, such other formulations proved to be unsuccessful and this is demonstrated by the following illustrative unsuccessful examples. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
             
               
             
           
               
                   
               
               
                 RUBBER COMPONENT FORMULA RDL5191 
               
               
                 Total Wt. = 3000 grams 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                   
                 PARTS 
                   
                   
               
               
                 CATEGORY 
                 Component Id. 
                 by weight 
                 Wt % 
                 Grams 
               
               
                   
               
               
                 Polymers 
                  1 Nordel IP NDR-4640 
                 80.00 
                 54.22 
                 1626.57 
               
               
                 Plasticizers 
                  2 Neoprene FB 
                 20.00 
                 13.55 
                 406.64 
               
               
                 Antioxidants 
                  3 Agerite Resin D 
                 2.00 
                 1.36 
                 40.66 
               
               
                 Fillers 
                  4 HiSil 233 
                 35.50 
                 24.06 
                 721.79 
               
               
                 Activator 
                  5 Zinc Oxide 
                 4.00 
                 2.71 
                 81.33 
               
               
                   
                  6 2nd Pass Additions 
               
               
                 Accelerators 
                  7 Rhenocure S/G 
                 0.80 
                 0.54 
                 16.27 
               
               
                   
                  8 Rhenocure AP-3 
                 3.85 
                 2.61 
                 78.28 
               
               
                   
                  9 Rhenocure ZADT/G 
                 1.00 
                 0.68 
                 20.33 
               
               
                 Curative 
                 10 Sulfur 
                 0.40 
                 0.27 
                 8.13 
               
             
          
           
               
                 Totals: 
                 147.55 
                 100.00 
                 3000.00 
               
               
                   
               
             
          
           
               
                 Mixing Instructions, first pass: 
               
               
                 Add Nordel and zinc oxide 
               
               
                 Add Hisil and antioxidant 
               
               
                 Add Neoprene FB 
               
               
                 Dump about 280 F. 
               
               
                 2nd Pass Additions 
               
               
                 Mix MB with curitives in Brabender 
               
               
                 Dump about 190 or below. 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
             
               
             
           
               
                   
               
               
                 RUBBER COMPONENT FORMULA RDL5570 
               
               
                 Total Wt. = 3000 grams 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                   
                 PARTS 
                   
                   
               
               
                 CATEGORY 
                 Component 
                 by weight 
                 Wt % 
                 Grams 
               
               
                   
               
               
                 Polymers 
                  1 Nordel IP NDR-4640 
                 50.00 
                 33.89 
                 1016.60 
               
               
                   
                  2 Nordel IP NDR-4520 
                 40.00 
                 27.11 
                 813.28 
               
               
                 Plasticizers 
                  3 Hypalon 20 
                 10.00 
                 6.78 
                 203.32 
               
               
                   
                  4 Akrochem P-133 
                 5.00 
                 3.39 
                 101.66 
               
               
                 Antioxidants 
                  5 Agerite Stalite S 
                 2.00 
                 1.36 
                 40.66 
               
               
                 Fillers 
                  6 HiSil 233 
                 35.50 
                 24.06 
                 721.79 
               
               
                 Activator 
                  7 Zinc Oxide 
                 4.00 
                 2.71 
                 81.33 
               
               
                   
                  8 2 nd  Pass Additions 
               
               
                 Accelerators 
                  9 Methyl Ethyl Tuads 
                 2.00 
                 1.36 
                 40.66 
               
               
                   
                 10 Monex or Unads 
                 1.00 
                 0.68 
                 20.33 
               
               
                   
                 11 Sulfads 
                 1.00 
                 0.68 
                 20.33 
               
               
                   
                 12 Butyl Zimate; 
                 1.50 
                 1.02 
                 30.50 
               
               
                 Curative 
                 13 Sulfur 
                 0.50 
                 0.34 
                 10.17 
               
             
          
           
               
                 Totals: 
                 152.50 
                 103.35 
                 3100.64 
               
               
                   
               
             
          
           
               
                 Mixing Instructions, first pass: 
               
               
                 Mix EPDMs and Hypalon together 
               
               
                 Add antioxidants 5 &amp; 6, Add silica, zinc oxide 
               
               
                 Add Akrochem resin. 
               
               
                 Dump about 250-300 
               
               
                 2nd pass Additions 
               
               
                 Mix MB with curitives in Brabender 
               
               
                 Dump about 190 or below. 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
             
               
             
           
               
                   
               
               
                 RUBBER COMPONENT FORMULA RDL 5571 
               
               
                 Total Wt. = 3000 grams 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                   
                 PARTS 
                   
                   
               
               
                 CATEGORY 
                 Component 
                 by weight 
                 Wt % 
                 Grams 
               
               
                   
               
               
                 Polymers 
                  1 Nordel IP NDR-4640 
                 50.00 
                 33.89 
                 1016.60 
               
               
                   
                  2 Nordel IP NDR-4520 
                 40.00 
                 27.11 
                 813.28 
               
               
                 Plasticizers 
                  3 Hypalon 20 
                 10.00 
                 6.78 
                 203.32 
               
               
                   
                  4 Akrochem P-133 
                 5.00 
                 3.39 
                 101.66 
               
               
                 Antioxidants 
                  5 Agerite Stalite S 
                 2.00 
                 1.36 
                 40.66 
               
               
                 Fillers 
                  6 HiSil 233 
                 35.50 
                 24.06 
                 721.79 
               
               
                 Activator 
                  7 Zinc Oxide 
                 4.00 
                 2.71 
                 81.33 
               
               
                 2nd Pass 
                  8 
               
               
                 Additions 
               
               
                 Accelerators 
                  9 Methyl Tuads 
                 0.75 
                 0.51 
                 15.25 
               
               
                   
                 10 Altax 
                 1.50 
                 1.02 
                 30.50 
               
               
                   
                 11 Sulfads 
                 0.75 
                 0.51 
                 15.25 
               
               
                   
                 12 Butyl Zimate 
                 1.50 
                 1.02 
                 30.50 
               
               
                 Curative 
                 13 Sulfur 
                 0.50 
                 0.34 
                 10.17 
               
             
          
           
               
                 Totals: 
                 151.50 
                 102.68 
                 3080.31 
               
               
                   
               
             
          
           
               
                 Mixing Instructions, first pass: 
               
               
                 Mix EPDMs and Hypalon together 
               
               
                 Add antioxidants 5 &amp; 6, Add silica, zinc oxide 
               
               
                 Add Akrochem resin. 
               
               
                 Dump about 250-300° 
               
               
                 2nd Pass Additions 
               
               
                 Mix MB with curatives in Brabender 
               
               
                 Dump about 190° or below. 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
             
               
             
           
               
                   
               
               
                 RUBBER COMPONENT FORMULA RDL 5572 
               
               
                 Weight = 3000 grams 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                   
                 PARTS 
                   
                   
               
               
                 Category 
                 Component 
                 by weight 
                 Wt % 
                 Grams 
               
               
                   
               
               
                 Polymers 
                  1 Nordel IP NDR-4640 
                 50.00 
                 33.89 
                 1016.60 
               
               
                   
                  2 Nordel IP NDR-4520 
                 40.00 
                 27.11 
                 813.28 
               
               
                 Plasticizers 
                  3 Hypalon 20 
                 10.00 
                 6.78 
                 203.32 
               
               
                   
                  4 Akrochem P-133 
                 5.00 
                 3.39 
                 101.66 
               
               
                 Antioxidants 
                  5 Agerite Stalite S 
                 2.00 
                 1.36 
                 40.66 
               
               
                 Fillers 
                  6 HiSil 233 
                 35.50 
                 24.06 
                 721.79 
               
               
                 Activator 
                  7 Zinc Oxide 
                 4.00 
                 2.71 
                 81.33 
               
               
                   
                  8 2nd Pass Additions 
               
               
                 Accelerators 
                  9 Methyl Tuads 
                 3.00 
                 2.03 
                 61.00 
               
               
                   
                 10 Methyl Zimate 
                 3.00 
                 2.03 
                 61.00 
               
               
                   
                 11 Sulfasan R 
                 2.00 
                 1.36 
                 40.66 
               
               
                   
                 12 Butyl Zimate 
                 3.00 
                 2.03 
                 61.00 
               
               
                 Curative 
                 13 Sulfur 
                 0.50 
                 0.34 
                 10.17 
               
             
          
           
               
                 Totals: 
                 158.00 
                 107.08 
                 3212.47 
               
               
                   
               
             
          
           
               
                 Mixing Instructions, first pass: 
               
               
                 Mix EPDMs and Hypalon together 
               
               
                 Add antioxidants 5 &amp; 6, Add silica, zinc oxide 
               
               
                 Add Akrochem resin. 
               
               
                 Dump about 250-300° 
               
               
                 2nd Pass Additions 
               
               
                 Mix MB with curitives in Brabender 
               
               
                 Dump about 190° or below. 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
             
               
             
           
               
                   
               
               
                 RUBBER COMPONENT FORMULA RDL 5172 
               
               
                 Total Wt = 3000 grams 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                   
                 PARTS 
                   
                   
               
               
                 Category 
                 Component 
                 by weight 
                 Wt % 
                 Grams 
               
               
                   
               
               
                 Polymers 
                  1 Nordel IP NDR-4640 
                 80.00 
                 54.22 
                 1626.57 
               
               
                   
                  2 Trilene 67A 
                 10.00 
                 6.78 
                 203.32 
               
               
                 Plasticizers 
                  3 Hypalon 20 
                 10.00 
                 6.78 
                 203.32 
               
               
                   
                  4 Akrochem P-133 
                 5.00 
                 3.39 
                 101.66 
               
               
                 Antioxidants 
                  5 Agerite Resin D 
                 2.00 
                 1.36 
                 40.66 
               
               
                 Fillers 
                  6 HiSil 233 
                 35.50 
                 24.06 
                 721.79 
               
               
                 Activator 
                  7 Zinc Oxide 
                 3.00 
                 2.03 
                 61.00 
               
               
                 2nd Pass 
                  8 
               
               
                 Additions 
               
               
                 Accelerators 
                  9 Captax 
                 1.00 
                 0.68 
                 20.33 
               
               
                   
                 10 Tellurac 
                 0.50 
                 0.34 
                 10.17 
               
               
                   
                 11 Sulfads 
                 0.75 
                 0.51 
                 15.25 
               
               
                 Curative 
                 12 Sulfur 
                 1.00 
                 0.68 
                 20.33 
               
             
          
           
               
                 Totals: 
                 148.75 
                 100.81 
                 3024.40 
               
               
                   
               
             
          
           
               
                 Mixing lnstructions, first pass: 
               
               
                 Mix Nordel and Hypalon together 
               
               
                 Add antioxidants 4 &amp; 6, Add silica, zinc oxide 
               
               
                 Add Trilene and Akrochem resin. 
               
               
                 Dump about 250-300° 
               
               
                 2nd Pass Additions 
               
               
                 Mix MB with curatives in Brabender 
               
               
                 Dump about 190° or below 
               
               
                   
               
             
          
         
       
     
     As indicated below, for various reasons, the above-described experimental test insulations proved to be unsuitable formulations for production of rocket motor insulations. 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 23 
               
             
             
               
                   
               
               
                 Unsuccessful Experiment Results 
               
             
          
           
               
                 Rheological Properties 
                   
               
             
          
           
               
                 Formulation 
                 ML 
                 MH 
                 ts2 
                 Tc(90) 
                 Rejected because: 
               
               
                   
               
               
                 RDL5571 
                 25.3 
                 138.3 
                 2.3 
                 21.3 
                 MH too high to match 
               
               
                   
                   
                   
                   
                   
                 existing standard 
               
               
                   
                   
                   
                   
                   
                 insulation 
               
               
                 RDL5572 
                 22.6 
                 173.9 
                 2.5 
                 25.7 
                 MH too high to match 
               
               
                   
                   
                   
                   
                   
                 existing standard 
               
               
                   
                   
                   
                   
                   
                 insulation 
               
               
                 RDL5570 
                 25.6 
                 128.6 
                 2.7 
                 29.5 
                 MH too high to match 
               
               
                   
                   
                   
                   
                   
                 existing standard 
               
               
                   
                   
                   
                   
                   
                 insulation 
               
               
                 RDL5191 
                 26.8 
                 133.6 
                 3.5 
                 25.4 
                 MH too high to match 
               
               
                   
                   
                   
                   
                   
                 existing standard 
               
               
                   
                   
                   
                   
                   
                 insulation 
               
               
                 RDL5172 
                 39.0 
                 128.0 
                 1.0 
                 25.0 
                 Uses the old cure system 
               
               
                   
                   
                   
                   
                   
                 as in TABLE 2, but 
               
               
                   
                   
                   
                   
                   
                 product is much too 
               
               
                   
                   
                   
                   
                   
                 scorchy to be useful; 
               
               
                   
                   
                   
                   
                   
                 cures at too low 
               
               
                   
                   
                   
                   
                   
                 temperature 
               
               
                   
               
             
          
         
       
     
     As these unsuccessful formulations indicate, and faced with the discontinuance of the availability of the hitherto thought to be essential component for the present standard insulation formulations, the development of a suitable and acceptable solid propellant rocket motor insulation that will provide the required performance criteria has not been an easy task. 
     The foregoing detailed description of the preferred embodiments of the invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Many modifications and variations within the scope of this invention will be apparent to practitioners skilled in this art. The illustrated embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated. It is therefore intended that the scope of the invention cover various modifications and equivalents included within the spirit and scope of the appended claims.