United States Patent (19) 11 Patent Number: 5,009,728 Chan Et Al
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United States Patent (19) 11 Patent Number: 5,009,728 Chan et al. (45. Date of Patent: Apr. 23, 1991 (54 CASTABLE, INSENSITIVE ENERGETIC 4,141,910 2/1979 Flanagan et al. ..................... 149/88 COMPOSITIONS 4,325,759 4/1982 Voigt et al. ..... - 49/19.92 4,361,526 11/1982 Allen ....................................... 264/3 (75) Inventors: May L. Chan; Alan D. Turner, both of 4,393,199 7/1983 Manser ................ ... 149/19.6 Ridgecrest, Calif. 4,426,540 1/1984 Shackelford et al. 149/19.91 4,456,494 6/1984 Maes et al. ........... ... 149/2 73) Assignee: The United States of America as 4,555,277 11/1985 Scribner ....... 149/19.4 represented by the Secretary of the 4,632,714 12/1986 Abegget al. ........................... 149/2 Navy, Washington, D.C. 4,764,316 8/1988 Brown et al..... ... 264/3.1 4,806,613 2/1989 Wardle......... ... 149/19.6 21 Appl. No.: 464,076 4,889,571 12/1989 Willer et al. ....................... 149/19.9 22 Filed: Jan. 12, 1990 OTHER PUBLICATIONS 51 int.C.'.............................................. C06B 45/10 52 U.S. C. ........................ ....... 149/19.1; 149/19.4; P. A. Mancinelli and S. O. Norris, "Macromonomers 149/19.5; 149/19.6; 149/19.9; 149/19.91; Lead to Acrylic Hot Melt and Solvent PSAs", reprint 149/88; 149/92 from Adhesives Age, Sep. 1985, (copy enclosed). (58) Field of Search .................... 149/19.4, 19.6, 199, Primary Examiner-Edward A. Miller 149/19.91, 19.1, 19.5, 88, 92 Attorney, Agent, or Firm-Donald E. Lincoln; Melvin J. (56) References Cited Sliwka; Sol Sheinbein U.S. PATENT DOCUMENTS (57) ABSTRACT 3,389,026 7/1968 Johnson ................................ 149/19 Energetic materials exhibiting low sensitivity comprise 3,480,490 1 1/1969 Finger et al. ... 149/92 a solid solution of nitroaliphatic oxidizer, preferably 3,501,357 3/1970 Suzuki et al. 149/19.9 trinitroethyl derivatives, in plasticized thermoplastic 3,778,319 12/1973 Benziger .......... a sa os saw son a a or 49/92 elastomer such as a block copolymer of polystyrene and 3,878,003 4/1975 Lo Presti et al. .................. 149/19.8 polyacrylate plasticized with dioctyl adipate. The ener 3,879,504 4/1975 Sherman et al. ........................ 264/3 3,932,241 1/1976 Sayles.................... ... 149/19.9 getic material is prepared by forming molten plasticized 3,943,209 3/1976 Lo Presti et al. ..................... 149/92 elastomer and then incrementally dissolving the oxi 3,953,258 4/1976 Sayles ............ ... 149/19.91 dizer in the molten binder. 3,959,042 5/1976 McCulloch et all ... 149/19.92 4,141,768 2/1979 Lo et al. ............................. 149/19.6 16 Claims, No Drawings 5,009,728 1. 2 No. 4,764,316. The bulk mixture is zone heated inside a CASTABLE, INSENSITIVE ENERGETIC cavity to form a solid propellant grain. This process COMPOSITIONS eliminates solvent. However, the solid grains produced by both of these patents have two phases and are shock Descripiton sensitive. 1. Technical Field Maes et al. in U.S. Pat. No. 4,456,494 discloses a This invention relates to a castable, insensitive, ener blasting composition including inorganic nitrate oxi getic composition and, more particularly, the present invention to a homogeneous energetic composition dizer and a gelling agent formed from an aqueous having minimum or no crystalline solid phase. 10 slurry. U.S. Pat. No. 3,389,026 discloses a plasticized 2. Background of the Invention explosive composition containing dissolved or col Existing castable, insensitive, energetic compositions loided polynitroaliphatic oxidizer (lines 10-18 of col. 2), generally have two distinct physical phases-a continu a nitropolymeric fuel and a plasticizer. McCulloch et al. ous phase consisting of a soft, rubbery binder and a in U.S. Pat. No. 3,959,042 discloses a gun propellant discontinuous phase consisting of a hard crystalline 15 composition formed by dispersing a polynitramine such explosive solid dispersed throughout the binder. Upon as RDX or HMX into an organic solution of a saturated shock or mechanical loading, separation or dewetting of polymer followed by precipitation. Sherman et al. in the binder and solid can easily occur causing a signifi U.S. Pat. No. 3,879,504 disclose an injection molded cant increase in sensitivity and a resulting increase in nitramine containing propellent formed from a mixture undesirable hazard properties. 20 Amorphous-type energetic compositions and emul of fine powder, oil or liquid elastomer and a catalyst. sion-type energetic compositions have been developed Abegg et al. discloses a solid energetic composition to avoid the phase separation problem. Known amor containing a thermoplastic elastomer. However, the phous energetic compositions are characterized by a fuel is emulsified by means of surfactants to disperse the single phase in which a polynitroaliphatic energetic 25 molten cxidizer into discrete oxidizer cells. Eutectic solid is completely dissolved in a nitropolymer fuel to mixtures of oxidizer salts are utilized to lower the tem form a soft, jelly-like material. Although amorphous perature. type compositions exhibit little or no crystal character under X-ray diffraction, they are impact sensitive and STATEMENT OF THE INVENTION have undesirable mechanical properties for most ener 30 It has been discovered according to the present in getic material applications. Emulsion-type energetic vention that energetic materials exhibiting a low degree compositions are characterized as a solid solution in which a solid crystalline explosive phase is dispersed in of sensitivity can be prepared from thermoplastic elasto a continuous solid binder phase. Ammonium Nitrate mers and nitroaliphatic oxidizers. Thermoplastic elasto (AN) emulsion-type compositions are prepared by mix 35 mers containing polar segments and thermoplastic elas ing an immiscible molten AN and molten binder with an tomers plasticized with oxygenated plasticizers have emulsifier to form a stable emulsion which becomes been found to dissolve or substantially dissolve certain solid upon cooling. Only limited numbers of AN eutec polynitroaliphatic energetic solids in a manner which tic mixtures melt at temperatures low enough to be inhibits extensive recrystallization upon cooling. The useful, thus limiting the energy level of the resulting resulting energetic material is homogeneous or amor composition. Additionally, vigorous mechanical agita phous in appearance and exhibits a high degree of insen tion is necessary to form the emulsion. The combination sitivity to external stimuli. of high temperatures and vigorous mechanical agitation Thermoplastic elastomers (TPEs) are used as binder of a molten explosive always creates some concern for safety during processing. material. The TPEs are heated and mixed with plasticiz Thermoplastic elastomers (TPE) are desirable as ers and a polynitroaliphatic oxidizer to form a true binders for composite propellants due to their ability to molten solution of oxidizer and binder during process form composite propellants without chemical cross ing. The TPE must be compatible with the oxidizer and linking. Crosslinked propellants cannot be redissolved. oxygenated plasticizer to form a miscible solution at Furthermore, they tend to become brittle with age. The 50 elevated temperatures. TPE binders are soluble, permitting lowering viscosity The energetic materials of the present invention have of the polymer in solution. Oxidizer salts can be dis a homogeneous state which provides a high degree of persed in the binder at lower energy and lower tempera insensitivity to external stimuli. The novel energetic ture. Furthermore, waste and obsolete propellant can be materials of the invention have the advantage of being safely returned to its components by remelting rather 55 ballistically tailorable for applications such as rocket than requiring burning or explosion to dispose of the propellants, gun propellants and explosives while still material. maintaining a high degree of insensitivity to external STATEMENT OF THE PRIOR ART stimuli. An example of solution dispersion of inorganic oxi The formulations of the present invention show par dizer in a solution of TPE binder is disclosed in U.S. ticular advantage as rocket propellants because the Pat. No. 4,361,526. The composite propellant can be materials have a very high combustion efficiency and a recovered by solution. However, use of solvent is unde high degree of insensitivity. The high combustion effi sirable for health and environmental reasons. ciency results from intimate contact between the fuel A composite propellant in which organic oxidizer and oxidizer in the homogeneous state. such as ammonium perchlorate (AP) and a nitramine These and many other features and attendant advan such as RDX or HMX is dispersed in a bulk polybutadi tages of the inventions will become apparent as the ene based thermoplastic binder is disclosed in U.S. Pat. description proceeds. 5,009,728 3 DETAILED DESCRIPTIONS OF THE O INVENTION The TPE can be a saturated hydrocarbon polymer such as polyethylene, polypropylene, polyisobutylene, Macromonomer Acrylate monomer or polystyrene, an unsaturated polymer such as polybu tadiene or polyisoprene or a hydrocarbon polymer con taining polar segments such as a polyester, polyether or (St) (), a polyurethane. There is higher compatibility and solu O where n is an integer such that the molecular weight of bility between the TPE and the nitroaliphatic oxidizer the macromonomer is from 500 to 50,000, R is H or when the TPE or the plasticizer includes oxygen con alkyl of 1-6 carbon atoms, R2 is alkyl of 1-6 carbon taining polar segments. The oxygenated plasticizers are atoms, M is the residue of reaction of the ethyl acrylate usually C1 to C10 alkyl esters of aliphatic or aromatic 15 group on the macromonomer with the acrylate group of hydrocarbon acids. The plasticized TPE contains at the comonomer, and x, y and z are integers. least 50% by weight plasticizer usually at least to 60% . The resulting SA type TPE has a continuous polar by weight plasticizer, preferably from 70 to 90% by polyacrylate backbone with pendant polystyrene weight.