bluuebunny/crossref_metadata_2025_split huggingface dataset:
Degradation of Elastomers 4. Continuous Chemical Stress Relaxation of Natural Rubber Vulcanizates
Authors: Scheele Walter , Hillmer Karl-Heinz 
Published: February 2011

Abstract
Temperature dependence of the chemical stress relaxation in oxygen of a series of natural rubber vulcanizates, extracted and unextracted, with the same pretreatment was investigated. Decrease of tension to about 50 per cent of the original was followed, using the half lives as a measure of velocity. The following observations were made: 1) Relaxation velocity of unextracted thiuram vulcanizates increases with increasing sulfur content; the activation energy decreases. 2) The relaxation velocities of extracted thiuram vulcanizates are independent of sulfur content of the mixtures and significantly greater than those of unextracted samples. This is caused by the loss of dithiocarbamate on extraction. 3) Other natural rubber vulcanizates (dithiocarbamate, MBT and peroxide vulcanizates) give the same relaxation half lives after extraction. 4) The relative importance of random scission and crosslink scission was discussed.
Molecular View of Fracture in Amorphous Elastomers
Authors: Halpin J. C. 
Published: February 2011

Abstract
Perhaps the first question coming to mind is, what does the strength of a body represent? It is natural to suppose that fracture of an elastomer involves rupture of molecular chains which interesect the fracture plane. The theoretical strength should then be the sum of the strengths of individual ruptured bonds. Computation of strength in this way involves estimating the number and nature of bonds to be broken and forces required. Bueche performed such a computation and his estimated strength was at least a thousand times as great as that usually observed. In essence, analysis suggests that rupture occurs before the average chain bond in a vulcanizate is anywhere near the maximum breaking load. A preliminary explanation for this effect was advanced by Bueche, who suggested that a specimen ruptures by a process which concentrates high local stress upon a few chains in the fracture cross section. The chains rupture under this high stress throwing stress on neighboring chains. The increased load on neighboring chains causes additional chain ruptures which in turn contribute to a repetitious process which is propagated at an increasing rate until rupture of the specimen occurs.
Survey of the Theory of Rubberlike Elasticity
Authors: Krigbaum W. R. , Roe Ryong-Joon 
Published: February 2011

Abstract
The problem of rubberlike elasticity has been under intensive investigation, both theoretically and experimentally, for over thirty years. The resulting literature has become so voluminous that adequate coverage, even at the survey level, demands the selection of a small segment of the overall problem. For this reason our review will deal exclusively with the reversible aspects of rubberlike elasticity. Furthermore, the historical development of the theoretical treatment is admirably covered in a number of recent books. Hence, our objective will be to present a fairly detailed and comprehensive survey of the current state of theory of rubberlike elasticity, and to compare this with pertinent experimental observations.
Reinforced Thermoplastics
Authors: Haward R. N. , Mann J. 
Published: February 2011

Abstract
If a thermoplastic is placed under load, as in a normal tensile tester, the characteristic stress strain curve is of the form given in Figure 1. Whether the material is described as tough or brittle depends on the relation between the fracture stress and the yield stress. In many cases the apparently irreversible deformation which takes place on yield is described as flow, but this is seldom, if ever, the case. The extension which takes place consists in the orientation of the tangled molecular network in a manner similar to that which occurs during extension of rubber, but with characteristic hard thermoplastics the deformation is opposed by viscous forces so that most of the energy applied is irrecoverably lost as heat. Deformations of this type are largely reversed on heating—as shown in the case of high-density polyethylene in Figure 2. In order to modify a brittle polymer to make it tougher we need to alter the relation between deformation and fracture so that, at least under short time tests, deformation takes place before fracture so that enough energy can be absorbed to cope with shock conditions. For this purpose the yield stress must be lower than the fracture stress. Naturally the ideal way of achieving this would be to raise the fracture stress, as any reduction in yield stress will normally lead to a softer and less rigid product. The extent and limitations of this problem will now be examined in relation to the styrene plastics.
Tires for Modern Roads
Authors: Tompkins E. S. 
Published: February 2011

Abstract
The following notes summarize a lecture which has been given to a number of sections of the Institution of the Rubber Industry and to Engineering Societies and other bodies over the past ten years. It has been revised and brought up to date from season to season. For the 1964–65 session it has a new title, emphasizing the recent closer understanding of the mechanism of tire grip in the wet. The lecture is divided into four sections :-(a) basic work the tire has to do; (b) components of the tire and the parts they play; (c) influence of the road; (d) examples of tires for modern roads.
Elastomers Based on Polycyclic Bisphenol Polycarbonates
Authors: Perry K. P. , Jackson W. J. , Caldwell J. R. 
Published: February 2011

Abstract
Polycarbonate elastomers were prepared by the addition of phosgene to a pyridine solution of poly (tetramethylene ether) glycol and bisphenols containing norbornane-type groups. These elastomers do not contain the classical “tie-down” points—crosslinks, hydrogen bonding, or crystallinity—which, heretofore, have been considered necessary for good elastomer properties. This work introduces a new concept in elastomer chemistry : bulky, three-dimensional groups are effective tie-down points. Most of the elastomers were prepared with 4,4′- (2-norbornylidene) bis(2,6-dichlorophenol). For comparison, several elastomers with bisphenol-A were also prepared. A statistically designed experiment was carried out to determine the effect of composition variables on the properties of these elastomers. The properties were determined on films cast from methylene chloride and, in many cases, on wet-spun fibers. These elastomers have elongations of 400–600 per cent and instantaneous elastic recoveries up to 100.
Effect of Certain Crystalline Substances on Physical Properties of Elastomers I. Stress-Strain behavior
Authors: Linnig Frederic J. , Parks Edwin J. , Stiehler Robert D. 
Published: February 2011

Abstract
Crystalline organic compounds containing a β-naphthyl group cause pronounced stiffening of rubber vulcanizates under certain conditions. When these materials are removed by extraction, the reinforcing effect vanishes. Reversibility of this effect indicates that the forces involved are not those associated with primary bonds. Reinforcement by at least one of these materials, PBNA, is obtained with vulcanizates made from various elastomers and vulcanizing agents, and is essentially independent of the state of cure. In some instances about five per cent of PBNA, the most effective of these, produces the same stiffness on first extension as 40 phr carbon black. Any PBNA dissolved in the rubber has no effect on stiffness. Thus, less than three per cent crystalline PBNA may produce an isotropic Young's modulus of about 20 kg/cm2 at room temperature. At higher concentrations of PBNA, strain continues to decrease but hardness does not change proportionally. The temperature coefficient of Young's modulus for PBNA reinforced rubber is negative, like that for vulcanizates containing carbon black. However, the increased solubility of PBNA with rising temperature makes quantitative determination of the temperature coefficient difficult. The PBNA-rubber structure is partly destroyed by repeated extensions to twice the original length. However after 5 extensions a substantial enhancement of modulus remains. Addition of PBNA to a rubber vulcanizate does not affect significantly the glass transition temperature. Though the reversible nature of reinforcement with PBNA strongly suggests a physical mechanism, the stiffening cannot be explained by existing theories of physical reinforcement.
Role of Ozone in Dynamic Cut Growth of Rubber
Authors: Lake G. J. , Lindley P. B. 
Published: February 2011

Abstract
The effect of ozone on the growth of cuts in rubber strips subjected to repeated tensile deformations has been investigated. At tearing energies below a critical value ozone accounts for all the cut growth, and in this region the rate of growth is substantially independent of tearing energy. At higher tearing energies, cut growth also occurs due to mechanico-oxidative rupture, the rate of this type of growth increasing rapidly with increasing tearing energy so that the effects of ozone are normally slight. For vulcanizates of natural rubber and SBR unprotected by anti-ozonant, the characteristics of dynamic ozone cut growth can be deduced from static measurements. If a natural rubber test piece is not allowed to relax to zero strain on each cycle, the effects of ozone are important over a wider range of tearing energy.
Reduced Variables and Integral Equations in Design of Plastics and Rubber Structures
Authors: Hopkins I. L. , Wentz R. P. 
Published: February 2011

Abstract
The long-time creep behavior of a hard rubber storage battery jar is analyzed by means of (a) reduced variables applied to stress relaxation in torsion, and (b) numerical solution of the integral equation connecting stress relaxation and creep. The validity of the integral relation is shown by calculation of creep in compression (ASTM D-621) from stress relaxation in torsion.
Relation of Modulus of Urethan Rubber to Molecular Weight of Polyester
Authors: Little Julian R. , Gregg Robert A. 
Published: February 2011

Abstract
The modulus of polyurethan rubber prepared from poly(ethylene propylene) (70–30) adipate and diphenylmethane diisocyanate by chain extension and cross-linking with water is proportional to the reciprocal molecular weight of the polyester diisocyanate. The modulus at a given molecular weight is lowered by chain extension of the polyester with diisocyanate. The modulus is increased 40 per cent by change of the diisocyanate to 1,5-naphthalene diisocyanate and reduced 60 per cent by change to 2,4-toluene diisocyanate.
New Vulcanizing Agents for Ethylene Propylene Elastomers. III
Authors: Wei P. E. , Serniuk G. E. , Rehner John 
Published: February 2011

Abstract
Perhalogenated bicycloalkenes, such as the Diels—Alder dimer of hexachloro-cyclopentadiene and perchloro-1, 1′-bis(2,2′-eyclopentene), can vulcanize saturated hydrocarbon elastomers like EPR when used in combination with sulfur. The activity is enhanced by the presence of certain metal compounds. In the vulcanization of EPR by means of the system octachlorocyclopentene/sulfur/metal compound, it is disadvantageous to replace the sulfur with conventional “sulfur donor” compounds or with conventional vulcanization accelerators. However, the vulcanizing activity of the system is enhanced by the presence of the dihydrochlorides of dithiodiformamidine, phenylenediamine, diaminotoluene, and diaminophenol, and also dichlorodimethylhydantoin and trichloroisocyanuric acid. The mechanism of vulcanization of saturated hydrocarbon elastomers by the system octachlorocyclopentene/sulfur/ferric oxide (or chloride) has been studied by chemical investigation of a model system. The experiments indicate that the perhalogenated compound is a chlorine donor. The chlorine reacts with ferric oxide and with sulfur to form a complex of ferric chloride and sulfur tetrachloride which is proposed as the primary vulcanizing species, serving to activate the hydrocarbon molecule by hydrogen abstraction. Supporting evidence was obtained by independent synthesis of the complex, and by demonstration that, in the presence of sulfur, it can crosslink polyethylene. This mechanism also provides a plausible explanation for the observed effects of amine hydrochlorides, and of “sulfur donors” or conventional accelerators when used in place of elemental sulfur, and for the fact that oxides of bivalent metals, in contrast to those of trivalent metals, fail to activate vulcanization by octachlorocyclopentene. Combinations of certain organic peroxides and perhalogenated compounds also can vulcanize EPR in the presence of sulfur and ferric oxide. When the stoichiometry of the components is favorable, one obtains synergistic effects between the two classes of agents on tensile strength. However, synergism is not observed with all members of these two classes.
New Vulcanizing Agents for Ethylene Propylene Elastomers. IV
Authors: Serniuk G. E. , Wei P. E. , Rehner John 
Published: February 2011

Abstract
Di(trichloromethyl) sulfone and dichloromethylene-bis(trichloromethyl sulfone) can vulcanize saturated hydrocarbon elastomers like EPR when used in combination with sulfur. The activity is enhanced by the presence of certain metal oxides. These agents are also effective in some other elastomers, and in their blends with EPR. They are also effective in combinations with octachlorocyclopentene, and with cumyl peroxide. Synergistic effects are observed in the tensile properties of such systems. Dichloromethylene-bis(trichloromethyl sulfone) is so active in EPR that it gives rise to scorch. Efforts to alleviate this drawback by the use of sulfur donor compounds or retarders, and by other means, have not yet proved to be successful. Di (trichloromethyl) sulfone appears to be quite tolerable as far as scorch is concerned, but its lachrymatory nature might be a disadvantage in large-scale non-vented processing operations. Chemical studies carried out with model systems indicate that perchloromethyl sulfones do not all follow the same mechanism in the vulcanization of saturated hydrocarbon elastomers. Reaction schemes are proposed for the behavior of some of the sulfones investigated.
High Temperature Elastomers for Extreme Aerospace Environments
Authors: Sieron J. K. 
Published: February 2011

Abstract
To meet the ever increasing environmental requirements imposed on sub-system components of advanced aerospace weapons systems, a comprehensive project to develop high strength, high temperature resistant elastomeric materials has been pursued. To attain this goal, research on reinforcement, stabilization, and crosslinking systems for butyl, ethylene propylene terpolymer, and fluoroelastomers was carried out. Results obtained in earlier work with the hydrocarbon elastomers disclosed that fine-particle-size, high-structure carbon black provided excellent tensile properties at high temperatures. Further work on stabilization systems resulted in the discovery that stannous oxide was effective for phenolic-resin-cured butyl at temperatures up to 500° F. For EPT, vulcanization-stabilization systems which provided a threefold improvement in useful life of this elastomer at temperatures in the range 300° F to 500° F were elucidated. Preliminary studies on fluoroelastomer reinforcement led to the finding that properly dispersed carbon fiber imparted not only better high temperature tensile strength, but also improved life at temperatures up to 600° F. In the present work, fibrous magnesium silicate, a material which normally would be used for dusting uncured rubber or as a paint filler, was found to be an effective reinforcing material for fluoroelastomers. Vulcanizates prepared with an acicular-platy form of this material have tensile strength at 400° F which is 80% greater than that with commonly used medium thermal carbon black. Hot tear strengths with even greater improvements were also realized, and as an added bonus, resistance to deterioration over a temperature range of 600° F to 700° F was also noteworthy. Primary implication of this work lies in renewed awareness that elastomeric vulcanizates are composite materials. Reinforcing materials as well as other additives are very influential in determining the engineering properties and performance of elastomers.
Controlled Instability of Polymers for Grid-Type Satellites
Authors: Snyder C. E. , Weir D. S. , Cross W. B. 
Published: February 2011

Abstract
A novel fabrication concept for passive communication satellite construction based on a wire grid reflective surface and a gas holding bladder that acts to deploy the structure is reported. Disappearance of this bladder or film web is advantageous for orbital stability. Likely polymer structures that permit formation of volatile fragments with no crosslinking are surveyed and from the disubstituted vinyl monomer family the n-butyl methacrylate ester is chosen. Physical demands on the bladder are met by this selection, and data are shown that demonstrate the feasibility of photolysis of monomer under conditions obtainable in orbit.
A Synthesis of Poly(2,4-Perfluoroalkylene-6-Perfluoroalkyltriazine)S
Authors: Dorfman Edwin , Emerson William E. , Cakr Russell L. K. , Bean C. Thomas 
Published: February 2011

Abstract
By thermal cyclodeamination reactions, perfluoroalkyleneimidines and perfluoroalkylamidines have been polymerized to give crosslinked triazine compositions. This reaction involves condensation of the reactants with elimination of ammonia and is illustrated in the formation of I. The amidines and imidines were prepared by the facile addition of ammonia to perfluoroalkane nitriles. Where the mono- and difunctional reactants were of comparable reactivity, essentially random condensations occurred so that gelled polymers were obtained. Properties of these gels varied, depending upon the reactant ratios used, from rather weak, gummy material to tougher inelastic polymers. Tensile strengths observed with these polymers generally ranged from 100 to 500 psi at about 100 per cent elongation. The triazine gels exhibited interesting thermal stability, showing no rapid decomposition up to 420° C; it was thought that with the discovery of a synthesis which would give linear, ungelled, triazine polymer that polymers having improved physical properties might be obtained.
Triazine Elastomers
Authors: Griffin W. R. 
Published: February 2011

Abstract
Three technically feasible routes have now been established for preparation of linear perfluoroalkylene triazine polymers. The most advanced route is based on addition polymerization of long chain fluorocarbon dinitriles and diamidines, followed by acylation and cyclodehydration to triazine polymer. Large research samples have been made, but crosslinking to thermally stable vulcanizates is still a problem. An alternate method, active halogen elimination from a difunctional fluorotriazine monomer, has been, demonstrated. High molecular weight polymer has been formed, but it is not elastomeric at room temperature. The low temperature flexibility is a function of structure and not of the method of polymerization, therefore other monomers with longer fluoroalkyl groups hold promise of elastomeric products. The route has attractive economics, but elastomeric products with crosslinking capability must be demonstrated. Coupling of diiodofluoroalkyl triazine monomers employing ultraviolet radiation has been demonstrated. This route is not being pursued because of research required and the predicted high cost of monomer preparation, when compared to the previous two routes. Evaluations of compounded vulcanized triazine elastomer show excellent resistance to hydrocarbon fuels and hydraulic fluids at 370° C and to long term air aging at 300° C. Tensile strength is in the 500 psi range, but is expected to improve with closer control of molecular weight and branching of the polymer. Excellent prospects are in view for fuel tank sealants, wire insulation and elastomer components for hydraulic systems useful in the 300° to 400° C range.
Poly-m-Carboranesiloxanes as Thermoresistant Elastomers
Authors: Scheoeder Hansjuergen , Schaffung Otto G. , Larchar Trescott B. , Frulla Floro F. , Heying Theodore L. 
Published: February 2011

Abstract
Selected members of the SiB polymer family were developed as elastomers for high temperature applications. To this end, polymerization procedures, processing technology, and testing techniques were extensively established. Progress of this work was judged from basic measurements, such as tensile strength, elongation, and hardness which were regularly performed at temperatures ranging from —80° F to 800° F, altogether on more than 300 molded test panels. With proper selection and concentration of reinforcing fillers and antioxidants, vulcanizates of SiB-2 and SiB-4 rubber exhibit outstanding heat-aging resistance. They show tensile strengths of 400–450 psi and elongations of 100–150% at ambient temperature, and withstand temperatures of 800° to 900° F in air, demonstrating a useful life of 24 hours and 2 hours, respectively. In addition, they were still found to be flexible at −40° to −80° F, thus indicating a wide range of elasticity. Certain specialty applications where thermal-oxidative stability is required are already being considered.
Hydrofluorocarbon High-Temperature Integral Fuel Tank Sealants
Authors: Anspach W. F. 
Published: February 2011

Abstract
Supersonic aircraft in the Mach 3 range have increased temperature requirements for many materials of construction. One of the most critical problem areas is the integral fuel tank where state-of-the-art elastomeric sealants no longer meet those requirements. New sealants resistant to hydrocarbon fuels at temperatures in excess of 500° F are urgently needed. A high temperature integral fuel tank filleting sealant has been developed based on a mixture of high and low molecular weight hydrofluoroearbon polymers. This sealant has a solids content of 85 per cent and cures at modest temperatures. It is a one component system stable for several weeks at ambient temperatures and for longer periods if refrigerated. The sealant exhibits good room temperature and high temperature mechanical properties both before and after aging in hydrocarbon fuel and fuel vapor at temperatures up to 500° F. A typical formulation showed an increase in tensile strength and better than 50 per cent retention of elongation after 1000 continuous hours exposure to fuel vapor at 500° F. Adhesion to metal substrates is good and samples have resisted rupture and loss of adhesion when pressurized at 500° F for 1000 hours. This is only an interim solution to the critical fuel tank sealant problem in Mach 3 aircraft. Research is continuing to improve its useable life and to eliminate a possibly serious corrosion problem with titanium substrates. It must be emphasized, however, that sealants based on hydrofluorocarbons, fluorosilicones, and other available elastomers can at best provide interim solutions to the high temperature sealant problems and that new base polymers, such as the triazine and polyether elastomers currently being developed by the Air Force Materials Laboratory, are needed to provide sealants which completely meet requirements.