US 4,915,755 AGranted

Filler reinforcement of polyurethane binder using a neutral polymeric bonding agent

OwnerChung S. Kiminventor

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Abstract

An effective neutral polymeric bonding agent (NPBA) is disclosed for a polar filler such as crystals of a nitramine (HMX or RDX, for example) dispersed in a polar binder, such as energetic binders containing nitro- and nitrato-plasticizers. The exceptional strength of the propellant composite of this invention is derived from a NPBA tailored to conform to criteria found to take advantage of the surface and absorption properties of the system so as to inculcate such strength. In particular, an interpolymer of acrylonitrile, methylacrylate and hydroxyethylacrylate can be tailored to provide a NPBA for a submix of a OH-terminated prepolymer and polar nitro- or nitratoplasticizers, such as nitroglycerine, which have solubility parameters in about the same range. Typically the submix includes HMX, RDX, ammonium perchlorate and the like along with fuel particles such as aluminum, boron, and the like.

Claims14

Dependent claims

A filler-reinforced propellant composite comprising,

(A) a binder matrix of polyurethane derived from a OH-terminated prepolymer and a polyfunctional isocyanate curing agent,
(B) a polar plasticizer,
(C) polar filler particles essentially insoluble in said binder matrix, said particles being in a size range large enough to benefit from interfacial bonding,
(D) non-nitrocellulosic neutral polymeric bonding agent, NPBA, free of amine and acid groups, having a pH in the range from 5.5 to 8.5, a molecular weight in the range from about 3000 to about 500,000 and having at least three OH groups per molecule for reaction with said curing agent, yet having sufficient reactive OH groups remaining to undergo primary chemical bonding with the binder matrix through reaction with the curing agent, said NPBA being present in an amount sufficient to be adsorbed on at least a portion of the surfaces of enough particles to provide a predetermined composite strength, said curing agent being present in an amount sufficient to provide enough reactive groups to react with substantially all OH groups in said prepolymer and all OH groups in said NPBA, whereby tensile strength of said composite with 50% filler loading, at 50% elongation of said composite, is at least double the tensile strength at 50% elongation of the same composite with the same loading but without a bonding agent.

1 more element

A process for preparing a filler-reinforced propellant composite, comprising,

(a) uniformly dispersing a non-nitrocellulosic neutral polymeric bonding agent free of amine and acid groups having a pH in the range from 5.5 to 8.5, and at least 3 OH groups per molecule, in a mixture of nitro- and/or nitratoplasticizer and OH-terminated prepolymer at an elevated temperature in the range from about 120.degree.-50.degree. F. to obtain a single phase;
(b) dispersing in said single phase, filler particles including solid oxidizer particles, optionally with metal fuel particles, metal hydrides, organic hydrides, and modifiers, to form a slurry;
(c) decreasing the temperature so as to approach the critical temperature of the neutral polymeric bonding agent for phase separation;
(d) mixing in a curing agent having OH-reactive functional groups in an amount sufficient to react with substantially all said reactive OH groups while maintaining the slurry in a fluent condition;
and,
(e) casting the fluent slurry in a molding cavity to cure at a curing temperature in the range from about 80.degree.-120.degree. F. until the composite is cured.

3 more elements

Dependencies are inferred from the claim text.