|||||||||| USO0520479A United States Patent (19) 11 Patent Number: 5,120,479 Chan et al. (45) Date of Patent: Jun. 9, 1992

(54) METHOD OF PREPARING CASTABLE, 3,449,179 6/1969 Minekawa et al...... 149/19.9 INSENSITIVE ENERGETIC COMPOSITIONS 3.50,357 3/1970 Suzuki et al...... 149/19.9 4,113,811 9/1978 Helfgen et al...... 264/3. 75) Inventors: May L. Chan; Alan D. Turner, both of 4,889,571 12/1989 Willer et al...... 149/19.92

Ridgecrest, Calif. 4,976,794 l2/1990 Biddle et al...... 49/19.5 4,978,482 2/1990 Johnson et al...... 264/3.1 73) Assignee: The United States of America as 4,985,094 1/1991 Nahlovsky et al...... 149/19.92 represented by the Secretary of the Navy, Washington, D.C. Primary Examiner-Edward A. Miller Attorney, Agent, or Firm-Stuart H. Nissim; Donald E. (21) Appl. No.: 643,915 Lincoln; Melvin J. Sliwka (22 Filed: Jan. 15, 1991 (57) ABSTRACT Related U.S. Application Data Energetic materials exhibiting low sensitivity comprise 62 Division of Ser. No. 464,076, Jan. 12, 1990, Pat. No. a solid solution of nitroaliphatic oxidizer, preferably 5,009,728. trinitroethyl derivatives, in a plasticized 51) Int. Cl...... CO6B 21/00 elastomer such as a block copolymer of and 52 U.S. Cl...... 264/3.1; 149/19.92 polyacrylate plasticized with dioctyl . The ener 58) Field of Search ...... 149/19.72; 264/3.1 getic material is prepared by forming molten plasticized elastomer and then incrementally dissolving the oxi (56) References Cited dizer in the molten binder. U.S. PATENT DOCUMENTS 3,389,026 6/1968 Johnson ...... 149/19.92 3 Claims, No Drawings 5, 120,479 1. 2 A composite propellant in which organic oxidizer METHOD OF PREPARING CASTABLE, such as ammonium perchlorate (AP) and a nitramine INSENSTIVE ENERGETIC COMPOSITIONS such as RDX or HMX is dispersed in a bulk polybutadi ene based thermoplastic binder is disclosed in U.S. Pat. This is a divisional of copending application: Ser. No. 5 No. 4,764,316. The bulk mixture is zone heated inside a 07/464,076 filed on Jan. 12, 1990, now U.S. Pat. No. cavity to form a solid propellant grain. This process 5,009,728. eliminates solvent. However, the solid grains produced by both of these patents have two phases and are shock TECHNICAL FIELD sensitive. This invention relates to a castable, insensitive, ener- 10 Maes et al. in U.S. Pat. No. 4,456,494 discloses a getic composition and, more particularly, the present blasting composition including inorganic nitrate oxi invention to a homogeneous energetic composition dizer and a gelling agent formed from an aqueous having minimum or no crystalline solid phase. slurry. U.S. Pat. No. 3,389,026 discloses a plasticized explosive composition containing dissolved or col BACKGROUND OF THE INVENTION 15 loided polynitroaliphatic oxidizer (lines 10-18 of col. 2), Existing castable, insensitive, energetic compositions a nitropolymeric fuel and a . McCulloch et al. generally have two distinct physical phases-a continu in U.S. Pat. No. 3,959,042 discloses a gun propellant ous phase consisting of a soft, rubbery binder and a composition formed by dispersing a polynitramine such discontinuous phase consisting of a hard crystalline as RDX or HMX into an organic solution of a saturated explosive solid dispersed throughout the binder. Upon 20 polymer followed by precipitation. Sherman et al. in shock or mechanical loading, separation or dewetting of U.S. Pat. No. 3,879,504 disclose an injection molded the binder and solid can easily occur causing a signifi nitramine containing propellent formed from a mixture cant increase in sensitivity and a resulting increase in of fine powder, oil or liquid elastomer and a catalyst. undesirable hazard properties. Amorphous-type energetic compositions and emul- 25 Abegg et al. discloses a solid energetic composition sion-type energetic compositions have been developed containing a thermoplastic elastomer. However, the to avoid the phase separation problem. Known anor fuel is emulsified by means of surfactants to disperse the phous energetic compositions are characterized by a molten oxidizer into discrete oxidizer cells. Eutectic single phase in which a polynitroaliphatic energetic mixtures of oxidizer salts are utilized to lower the tem solid is completely dissolved in a nitropolymer fuel to 30 perature. form a soft, jelly-like material. Although amorphous STATEMENT OF THE INVENTION type compositions exhibit little or no crystal character under X-ray diffraction, they are impact sensitive and It has been discovered according to the present in have undesirable mechanical properties for most ener vention that energetic materials exhibiting a low degree getic material applications. Emulsion type energetic 35 of sensitivity can be prepared from thermoplastic elasto compositions are characterized as a solid solution in mers and nitroaliphatic oxidizers. Thermoplastic elasto which a solid crystalline explosive phase is dispersed in mers containing polar segments and thermoplastic elas a continuous solid binder phase. Ammonium Nitrate tomers plasticized with oxygenated have (AN) emulsion-type compositions are prepared by mix been found to dissolve or substantially dissolve certain ing an immiscible molten AN and molten binder with an 40 polynitroaliphatic energetic solids in a manner which emulsifier to form a stable emulsion which becomes inhibits extensive recrystallization upon cooling. The solid upon cooling. Only limited numbers of AN eutec resulting energetic material is homogeneous or amor tic mixtures melt at temperatures low enough to be phous in appearance and exhibits a high degree of insen useful, thus limiting the energy level of the resulting sitivity to external stimuli. composition. Additionally, vigorous mechanical agita- 45 Thermoplastic elastomers (Tpes) are used as binder tion is necessary to form the emulsion. The combination material. The TPEs are heated and mixed with plasticiz of high temperatures and vigorous mechanical agitation ers and a polynitroaliphatic oxidizer to form a true of a molten explosive always creates some concern for molten solution of oxidizer and binder during process safety during processing. ing. The TPE must be compatible with the oxidizer and Thermoplastic elastomers (TPE) are desirable as 50 oxygenated plasticizer to form a miscible solution at binders for composite propellants due to their ability to elevated temperatures. form composite propellants without chemical cross The energetic materials of the present invention have linking. Crosslinked propellants cannot be redissolved. a homogeneous state which provides a high degree of Furthermore, they tend to become brittle with age. The insensitivity to external stimuli. The novel energetic TpE binders are soluble, permitting lowering viscosity 55 materials of the invention have the advantage of being of the polymer in solution. Oxidizer salts can be dis ballistically tailorable for applications such as rocket persed in the binder at lower energy and lower tempera propellants, gun propellants and explosives while still ture. Furthermore, waste and obsolete propellant can be maintaining a high degree of insensitivity to external safely returned to its components by remelting rather stimuli. than requiring burning or explosion to dispose of the 60 The formulations of the present invention show par material. ticular advantage as rocket propellants because the materials have a very high combustion efficiency and a STATEMENT OF PRIOR ART high degree of insensitivity. The high combustion effi An example of solution dispersion of inorganic oxi ciency results from intimate contact between the fuel dizer in a solution of TPE binder is disclosed in U.S. 65 and oxidizer in the homogeneous state. Pat. No. 4,361,526. The composite propellant can be These and many other features and attendant advan recovered by solution. However, use of solvent is unde tages of the inventions will become apparent as the sirable for health and environmental reasons. description proceeds. 5, 120,479 3 DETAILED DESCRIPTIONS OF THE INVENTION O R1 H O (ST)-O-C-C=CH -- CH=C-C-OR The TPE can be a saturated hydrocarbon polymer Macromonomer Acrylate monomer such as , , polyisobutylene, or polystyrene, an unsaturated polymer such as polybu tadiene or polyisoprene or a hydrocarbon polymer con -A-M-A-M-A- taining polar segments such as a , polyether or (St) (St) a . There is higher compatibility and solu O bility between the TPE and the nitroaliphatic oxidizer where n is an integer such that the molecular weight of when the TPE or the plasticizer includes oxygen con the macromonomer is from 500 to 50,000, R is H or taining polar segments. The oxygenated plasticizers are alkyl of 1-6 carbon atoms, R2 is alkyl of 1-6 carbon usually C1 to Clo alkyl esters of aliphatic or aromatic atoms, M is the residue of reaction of the ethyl acrylate hydrocarbon acids. The plasticized TPE contains at 15 group on the macrononomer with the acrylate group of least 50% by weight plasticizer usually at least to 60% the comonomer, and x, y and z are integers. The resulting SA type TPE has a continuous polar by weight plasticizer, preferably from 70 to 90% by polyacrylate backbone with pendant polystyrene weight. groups providing a dispersed hydrocarbon domain. The Suitable TPEs include thermoplastic , 20 SA type TPE usually contains from about 25 to about , ; polyethers and the follow 50% macromononer. ing block copolymers: A representative macromonomer. CHEMLINK(R) styrene-isoprene-styrene block copolymer; 4500, is a 2-polystyryl ethyl methacrylate of the for mula: styrene-ethylene/butylene-styrene block copolymer; 25 polystyrene-polyacrylate copolymer; ethylene-vinylacetate copolymer; polyacrylate--isoprene copolymer; and vinylacetate-aliphatic polyester copolymer. The thermoplastic elastomers are graft copolymers of 30 a prepolymerized macromonomer segment terminating in a polymerizable end group such as a vinyl group and a monomer. This results in a linear, comb-type copoly where n is an integer such that the molecular weight is mer of the monomer and the vinyl group of the mac 35 about 13,000. romonomer having side chains of the prepolymer pen A SA type TPE containing about equal amount of dant from the backbone of the copolymer. There is CHEMLINK(R) 4500, 2-polystyryl ethyl methacrylate, wide versatility in the control of the properties of the and methyl acrylate was utilized in the compositions resulting thermoplastic elastomer. The backbone can 40 tested in Tables 2-8 which follow. have polar properties while the side chains can be oleo Plasticizers used in the present invention include: philic hydrocarbon or vice versa. dioctyl adipate (DOA): The macromonomer usually has a molecular weight acetyl triethyl citrate (ATEC); from 500 to about 50,000 usually about 5,000 to 25,000. triacetin (TA); and 45 trioctyl trimellitate (TOTM). Representative macromonomers are styrene-isoprene Polynitroaliphatic oxidizers are best suited for use copolymer, styrene-ethylene copolymer polystyrene with the TPEs and oxygenated plasticizer of the ethylene, polyacrylate and polyvinyl acetate. present invention. Particularly useful are polyni The polymerizable comonomer can be styrene, buty troalkyl derivatives in which the alkyl contains lenestyrene, acrylate, vinyl acetate, isoprene or polyes 50 from 1-5 carbon atoms. Preferred oxidizers are ter. The macromonomer is end capped with a group trinitroethyl derivatives such as trinitroethylnitra copolymerizable with the monomer, usually of the same mines, trinitroethylcarbonates, trinitroethylfor type. For example, the polystyrene macromonomer mates, trinitroethylureas, and trinitroethylformals. terminates in an acrylate group when copolymerized Specific examples include: 55 trinitroethylorthocarbonate (TNEOC); with a vinyl-containing monomer, usually of the same trinitroethylorthoformate (TNEOF); type. For example, the polystyrene macromonomer bis(trinitroethyl)nitramine (BTNEN); terminates in an acrylate group when copolymerized bis(trinitroethyl)carbonate (BTNEC); with an acrylate comonomer. trinitroethylformal (TNEF); Styrene-acrylate TPE based on acrylate modified bis(trinitroethyl)urea (BTNEU); polystyrene macromonomers are disclosed in U.S. Pat. tetrakis(trinitroethoxy)ethane (DITEFO); No. 3,786,116, the disclosure of which is incorporated trinitroethylnitroguanidine (TNENG); and herein by reference. These materials have been con octanitro-diazaoctane (ONDO). Processing the homogeneous energetic materials is mercially utilized in solvent based and hot melt pressure 65 accomplished in the following steps: sensitive adhesives. thermoplastic elastomer is melted at temperatures The styrene/acrylate (SA) TpE can be represented as ranging from 100° C. to about 200 C. depending follows: on the elastomer; solubie plasticizer is mixed into 5, 120,479 5 6 the TPE as the mixture is cooled to a temperature were conducted on selected compositions. The results of 90° C. to about 110° C. indicated that they have substantial gain in favorable energetic solid is added in multiple increments with sensitivity characteristics as compared to compositions slight mechanical stirring as the TPE mixture is made with the same solid ingredient by the conven maintained at a temperature of 80 C. to about 100 5 tional methods. C. The material is then cast. The TPE generally constitutes about 3% to about 9% TABLE 4 by weight and the plasticizer about 10-30% by weight Small Scale Sensitivity Test Results of the total composition. Formulations containing about Calculated 65% to about 85% by weight of energetic solid have 10 Performance been found to work well. Sample Composition sp Density Sensitivity The following Table 1 illustrates the impact, friction PE/ATECATNEOF 245 sec 1.65 g/cc "Impact: 30 m and electrostatic sensitivities of some energetic solids (80%) (honogeneous) with 2.5 kg Mild cook-off used in the present invention. "Small scale TABLE 1 15 shock sensitiv Safety Test Data on Various Trinitroethyl ity: NO GO: 120 Derivatives. cards Electrostatic PEG/TEGDNATNEOF 244 sec 1.62 g/cc DETONATION in Impact 2. Kg ABL, lbs. Sensitivity, (62%) (single phase) slow cook-off 50%, cn 50% 0.25 J 2O ONDO 9.0 402 10/10 NF TNENG 9.0 616 0/10 NF TABLE 5 BTNEU 16.0 457 10/10 NF Safetv Test Results NEOF 8.0 568 10/10 NF Impact. cm Friction. ABL Electrostatic HMX - 14 cm 25 Weight 7% TNEOF 2.5 Kg 1000 lbs. 0.25 J 70 72 10/10 NF 10/10 NF Trinitromethyl derivatives are known to be impact 80 30 A F 10/10 NF sensitive solids and TNEOF is no exception. The neat 85 22 10/10 NF 10/10 NF solid is more impact sensitive than HMX. However, when it is incorporated in the TPE/ATEC binder, substantial gain was evident in the impact sensitivities. Tables 6-8 provide calculated Specific Impulse and They were raised to 22-72 cm (as shown in Table 2) Density data for several formulations. Each table pro depending on the solid level (85-70%). In comparison, vides the Specific Impulse and Density for varying samples containing conventional binders such as PEG/ weight percentages of solid explosive and for binders TEGDN and GAP/GAP-NO2 binder with solid load containing different plasticizers. The binders for all ing at 62-65% were shown to have impact sensitivities 35 formulations contain a 3:1 ratio of plasticizer to thermo in 9-12 cm range. elastomer (TPE). The TPE used in all formula TABLE 2 tions of Tables 2-8 is a copolymer of polystyrene and Safety Test Data on TNEOF Based Propellants. polyacrylate. The plasticizers listed in the tables are: Electrostatic 40 dioctyl adipate (DOA), acetyl triethyl citrate (ATEC), impact 2.5 Kg Friction. ABL Sensitivity and triacetin (TA). The explosive solid of Table 6 is Wt 7. TNEOF 50% cm 1000 lbs. 0.25 J trinitroethylorthocarboante (TNEOC). Tetrakis)trini 70 72 O/10 NF 10/10 NF troethoxy)ethane (DITEFO) is the explosive solid of 80 30 l/l F 10/10 NF Table 7 and trinitroethylorthoformate (TNEOF) is the 85 22 10/10 NF 10/10 NF 45 explosive solid of Table 8. TABLE 6 The thermal analyses of neat TNEOF and TPE/A- TEC/TNEOF (80%) are shown in Table 3. The ther Specific Impulse & Density for TNEOC Based mal decomposition of TNEOF appears to be the domi Propellant Compositions nating mechanism for the propellant material since the Plasticizer Percent bv. Weight of the Oxidizer temperatures for weight loss and peak exotherms are 50 Type 78% 80% 82% 84% very similar between neat solid and propellant sample. DOA-sec. 236.0 242.0 247.5 252.5 -g/cc 5248 1.5488 15736 1.5991 TABLE 3 ATEC-sec. 244.7 248.8 252.4 255.4 Thermal Analyses of TNEOF and TNEOF Based Propellant *g/cc .6068 .6253 1.6444 1.6638 Composites. 55 TA-sec 246.1 249,8 253. 255.7 TNEOF TPE/ATEC2/TNEOF (80%) -g/cc 1.6167 1.6346 1.6529 1.6716 TGA Plasticizer/polymer = 3.0 Onset C. 52 150 % Wt. loss, C. 62 156 TABLE 7 10% Wt. loss, C. 82 70 DSC Specific Impulse & Density for DITEFO Based Onset C. 165 149 Propellant Compositions Peak Exotherm, C. 205 210 Plasticizer Percent by Weight of the Oxidizer Shows an endotherm at 128 C. 129" Type 78% 80% 82% 84% B.P. for ATEC is 135 C. (1 mm Hg) 65 DOA-sec 228.4 234.7 240.6 246. -gcc 1.5204 .544 5686 1.5938 Tables 4 and 5 present the results of preliminary ATEC-sec 238.4 242.9 247.1 250.9 small-scale sensitivity tests (which include impact, elec -g/cc 608 16201 1.6389 6581 trostatic, friction, shock and slow cook-off tests) which TA-sec 240. 244.3 248.1 25.6 5, 120,479 7 8 are approximately 5 to 10% greater than state-of-the-art TABLE 7-continued gun propellants such as LOVA gun propellant. Specific Impulse & Density for DITEFO Based Propellant Compositions TABLE O Plasticizer Percent by Weight of the Oxidizer 5 Calculated Performance For Gun Propellant Application Type 78 c. 80% 82% 84% TNEOF (wt %) 80 82 84 -g/cc 87 16293 1.6474 6658 Mass impetus (J/g) 32 1140 14 Plasticizer/polymer = 3.0 Flame temperature (K.) 3585 3684 3762

TABLE 8 O In summary the plasticized polar thermoplastic elas Specific Impulse & Density for TNEOF Based tomer binder of the invention is able to dissolve the Propellant Compositions nitroaliphatic oxidizer at elevated temperature and Piasticizer Percent by Weight of the Oxidizer cools to provide compositions with little or no crystal Type 780. 80% 82% 84% lites. The energetic composition of the invention has DOA-sec. 232.3 238.6 244.2 249.6 5 low sensitivity with high combustion efficiency. The -gacc 15513 5769 16033 1.6.306 composition can be used as a propellant or an explosive. ATEC-sec. 24.6 245.9 249.9 253.3 The solid levels depend on the performance require -g/cc .6362 16563 16768 6979 A-sec. 243.2 247.2 250.8 253.9 ments for different systems. g/cc 6465 16159 6857 1706 It is to be realized that only preferred embodiments of Plasticizer? polymer s 3.0 the invention have been described and that numerous substitutions, modifications and alterations are permissi Table 9 provides theoretical performance of a typical ble without departing from the spirit and scope of the formulation of the present invention for explosive appli invention as defined in the following claims. cation as calculated by Kamlet's method. Performance We claim: characteristics are calculated for varying weight per 25 1. A method of preparing a cast homogeneous, insen centages of trinitroethylorthoformate (TNEOF) explo sitive energetic composition comprising the steps of: sive solid. The binder consists of 3 parts by weight melting a thermoplastic elastomer at a temperature acetyl triethyl citrate (ATEC) to part thermoplastic from about 100 C. to about 150 C.; elastomer. A copolymer of polystyrene and polyacryl dissolving a plasticizer in the molten thermoplastic ate was used as the thermoplastic elastomer. 30 elastomer to form plasticized thermoplastic elasto mer, said plasticized thermoplastic elastomer being TABLE 9 capable of dissolving a nitroaliphatic oxidizer; Calculated Performance for Explosive Application adding nitroaliphatic oxidizer to the molten plasti TNEOF (wt %) 80 84 85 cized thermoplastic elastomer and dissolving the Detonation 247 267 273 35 oxidizer therein to form a castable composition; Pressure (Kbar) casting the composition to form a shaped article; and Detonation 7.72 7.97 8.03 Velocity (mm/u sec) cooling under conditions effective to provide an Cylinder Energy 0.95 1,02 1,04 energetic composition having only a small amount G6 mm (KJ/g) or no crystallites of said nitroaliphatic oxidizer. Cylinder Energy 1.2 3 1.32 40 2. A method according to claim 1 in which the ni G19 inn (KJ/g) troaliphatic oxidizer is added to the molten elastomer in increments. Table 10 provides theoretical performance of a typi 3. A method according to claim 2 further including cal formulation of the present invention for gun propel the step of cooling the plasticized elastomer to tempera lant application as calculated by Kamlet's method. The “5 ture below 120° C. before adding the oxidizer. theoretical performance of the following compositions sk k k k

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