Stable plasticizers for nitrocellulose/nitroguanidine-type compositions

Abstract: Stable plasticizer system and corresponding nitrocellulose/nitroguanidine nitramine-type propellant compositions utilizing such system. A mixture of a high energy nitratolkyl nitramine and a second nitrato alkyl nitramine having a lower energy content is used as plasticizer system.

Description: The present invention relates to stable propellant compositions of low sensitivity comprising matter and energy adjustment/plasticizer components and corresponding method for improving storage life by utilizing a stable plasticizer system. Most conventional gun propellants comprise a matrix component such as nitrocellulose with various nitrate esters such as nitroglycerine, and/or nitroguanidine, such high energy compositions unfortunately, can be easily set off or initiated by neighboring explosions. One promising approach for developing less sensitive gun propellants has involved the use of high-energy nitraamines such as alkyl nitrato nitramines as substitutes for such sensitive esters in multi-based propellants. Nitraamines of such type, their substitution and preparation, are disclosed, for instance, in U.S. Patent 2,461,582 of Wright et al. and in U.S. Patent 2485855 of Blomquist et al., using ethanol-amine or N-alkyl substituted ethanol-amine and acetic anhydride as reactants. As noted in Blomquist, however, there is a tendency for high energy nitramines to migrate and crystallize out of nitrocellulose during storage, resulting in substantial unplanned changes in sensitivity and ballistic properties. This problem is dealt with by utilizing a propellant composition comprising A. a matrix component, such as nitrocellulose, and/or the like, B. an energy adjustment component; and C. an effective amount of plasticizer component capable of gelation of the matrix component and comprising (i) a high energy nitrato alkyl nitramine (i.e. based on heat of explosion) of the formula in which R is defined as a -Alk-O-NO₂, H, or a 1-2 carbon monovalent aliphatic group; and Alk is individually defined as a 1-2 carbon divalent aliphatic chain; said high energy alkyl nitramine being at least partly soluble or miscible in ii. a second nitrato alkyl nitramine having a lower energy content (i.e. heat of explosion) than the high energy nitramine component of Formula I and represented by the formula in which R' is individually defined as a 2-5 carbon monovalent aliphatic group of different molecular structure from the R group of formula I and n is a positive integer not exceeding about 2, the ratio of A./B./C. components of the propellant composition being 4-5/1-2/2-4 in parts by weight based on propellant composition, in the cumulative presence of up to about 6% by weight, based on propellant composition, of one or more conventional additive comprising a stabilizer such as ethyl centralite, an opacifier such as carbon black, a flash suppressant such as KNO₃ or K₂SO₄, and the like. For present purposes the ratio by weight of high energy nitrato alkyl nitramine-to-nitramine lower energy in the (C.) component is preferably 1-5 to 5-1 in parts by weight, and the R and R' substituent groups within formulae I and II are molecularly dissimilar in each plasticizer component. Of particular interest, for present purposes, is the use of normally solid high energy nitrato ethyl nitramine ingredients in which the definition of R in formula I is nitratoethyl or methyl, and Alk is -CH₂CH₂-, while the R' group (formula II) is preferably a 2 to 4 carbon monovalent alkyl group such as an ethyl, propyl or butyl substituent. The term "matrix component" for purposes of the present invention can include one or more of nitrocellulose, cellulose acetate, cellulose acetate butyrate, ethyl cellulose, ethyl acrylate-based polymer, and styrene-acrylate type copolymer. The term "energy adjustment component," for present purposes, comprises generally insoluble energetic solids such as one or more of nitroguanidine, RDX, HMX and ethylene dinitramine (EDNA) and similar recognized components. The term "effective amount", for purposes of the present invention, is defined as about 25%-65% by weight of binder component of the propellant composition (binder not including solids). Nitratoethyl nitramines of interest for purposes of formula I and II components along with pertinent, physical characteristics is set out in Tables I and II below, in which energy content of each component is set out as calculated heat of explosion in J/g (cal/gm). Cpd# Solubility Parameter 1 13.1 2 13.2 3(4) 11.4 5 11.0 6 10.6 7 10.4 Example I A. A 22,68kg (50 lb.) batch of test propellant composition consisting of nitrocellulose (39.5 % by wt.), nitroguanidine (22.5%), ethyl centralite (1.5%), potassium sulfate (1%), carbon black (0.5%) and methyl nitrato ethyl nitramine derivative (35%) of the formula (obtained from methyl ethanolamine, nitric acid, and acetic anhydride in accordance with the process as described in col 4 of U.S. Patent 2,485,855) is prepared by initially blending nitrocellulose, ethyl centralite, potassium sulfate (1%) and carbon black in indicated amounts with a 50/50 acetone/ethanol solvent at ambient temperature at 25 rpm for about 10 minutes. To this is then added the methyl-nitratoethyl nitramine component premixed in 50/50 acetone/ethanol solvent, and the combined material blended for 1 hour to obtain a colloided nitrocellulose phase. Into this phase is slowly mixed dry nitroguanidine component and blended for about 1 hour, to obtain a homogeneous dough-like consistency. The dough is then put through a 10.16cm (4-inch) extrusion press having a plurality 1.143 cm of (.45 inch) diameter die holes to obtain correspondence extruded strands which are then conventionally cut into 1.524cm (0.6") lengths, air dried at room temperature for 1 day then subject to a 55 C long drying phase for 3 days. The resulting granular propellent is stored at ambient temperature and examined after 1 week. Observed results are reported in Table IV below. B. The process of IA, is repeated using 46.5 parts by weight of the methyl nitratoethyl nitramine mixed with 52.5 parts nitrocellulose and 1 part ethyl centralite stabilizer. No nitroguanidine was added. After drying and storage steps identical to Ex. 1A, the propellant is evaluated and results reported in Table IV below. C. The process of IA is repeated using 25 parts by weight of the methyl nitratoethyl nitramine mixed with 74 parts of nitrocellulose and 1 part of ethyl centralite. After drying and storage steps identical to Ex. 1A, the propellant is evaluated and results reported in Table IV below. D. The process of IA, is repeated except that the relative amounts and the type of insoluble, energetic solid are mixed as follows, with respect to nitrocellulose (16.1%), nitroguanidine (26.5%), cyclonite or RDX (47.9%), ethyl centralite (0.4%), carbon black (0.1%), KNO₃ (1%), the methyl nitratoethyl nitramine (4.6%) (cpd 2, Table I) and the ethyl nitratoethyl nitramine (3.4%) (cpd 4, Table II). The observed results are reported in Table IV below. E. The process of Ex. IB is repeated except that the relative amounts of ingredients are mixed as follows, with respect to nitrocellulose (47.8%), nitroguanidine (15%), ethyl centralite (1%), KNO₃ (1%), carbon black (0.2%), the methyl nitrato ethyl nitramine (20%) (cpd 2, Table 1) and the ethyl nitrato ethyl nitramine (10%) (Cpd 4 Table II). The observed results are reported in Table IV below. Example Observed Surface Crystallization 1A (++) 1B (++) 1C (+) 1D (-) 1E (-)

Claims: A propellant composition comprising, in combination, A. a matrix component; B. an energy adjustment component; and C. an effective amount of a plasticizer component capable of gelation of said matrix component and comprising i. a high energy nitratoalkyl nitramine of the formula in which R is defined as -Alk-O-NO₂, H, or a 1-2 carbon monovalent aliphatic group; and Alk is individually defined as a 1-2 carbon divalent aliphatic chain; said high energy alkyl nitrato-nitramine, being at least partly soluble or miscible in component II; and further comprising ii. a second nitrato alkyl nitramine having a lower energy content than said high energy nitrato alkyl nitramine component, and represented by the formula in which R' is individually defined as a 2-5 carbon monovalent aliphatic group of different molecular structure from the R group of formula (I) and n is defined as a positive integer not exceeding 2, the ratio of A./B./C. components of said propellant composition being 4-5/1-2/2-4 in parts by weight based on propellant composition, in the cumulative presence of up to 6% by weight, based on propellant composition, of one or more additive selected from the group consisting of a stabilizer an opacifier, and a flash suppressant. A propellant composition of claim 1 wherein the ratio by weight of said A./B./C. components is 4.5/1.5/2.0 based on propellant composition. A propellant composition of claim 1 wherein the ratio by weigh of A./B./C. components is 4.8/1.5/3.5, based on propellant composition. A propellant composition of claim 1, wherein the ratio by weight of A./B./C. components is 5.0/2.0/4.0 based on propellant composition. A propellant composition of claim 2, wherein the energy adjustment component is nitroguanidine and the matrix component is nitrocellulose. A propellant composition of claim 3, wherein the energy adjustment component is nitroguanidine and the matrix component is nitrocellulose. A propellant composition of claim 4, wherein the energy adjustment component is nitroguanidine and the matrix is nitrocellulose. A method for improving the storage life of double based low sensitivity propellant composition comprising a matrix component A, an energy adjustment component B and a nitratoalkyl nitramine plasticizer component C, the ratio of A/B/C components of said propellant composition being 4-5/1-2/2-4 in parts by weight based on propellant composition, comprising the steps of a) initially dissolving at least one high energy nitratoalkyl nitramine of the formula in which R is defined as -Alk-O-NO₂, H, or a 1-2 carbon monovalent aliphatic group, and Alk is individually defined as a 1-2 carbon divalent aliphatic chain; at least in part into a second nitrato alkyl nitramine component having a lower energy content than said nitramine of formula I and represented by the formula in which R' is defined as a 2-5 carbon monovalent aliphatic group of different molecular structure from the R group of said high energy nitramine component, and n is defined as a positive integer not exceeding 2; (b) admixing and blending the resulting combined plasticizer component into said matrix component to obtain a dough-like mixture; and (c) blending an energy adjustment component into said dough-like mixture to obtain an extrudable essentially homogeneous mass; (d) extruding said essentially homogeneous mass to obtain strands of propellant material and (e) cutting and drying said strands to obtain the desired propellant composition. The method of claim 8 wherein the matrix component is nitrocellulose and the ratio of high energy nitratoalkyl nitramine (formula I)-to-second nitramine (formula II) in said plasticizer component is 1-5 to 5-1. The method of claim 8 wherein the high energy nitramine of formula I and the second nitrato alkyl amine of formula II are initially dissolved in a common solvent system prior to blending into said matrix component.

Inventors: ZEIGLER EDWARD HAYS, ZEIGLER, EDWARD HAYS
Applicants: HERCULES INC, HERCULES INCORPORATED
Application year: 1991
Main classification: C06B45
IPC codes: C06B45, C06D5, C06B25