Heat-expandable beads as burning rate accelerators

Claim 1

In a propellant composition selected from a composite propellant composition or a composite-modified, double-base propellant composition, said composite propellant composition consisting essentially in weight percents of the ingredients as follows: ______________________________________ aluminum powder 12.0 ammonium perchlorate (70 μm) 73.0 N-hexylcarborane 6.0 hydroxyl-terminated polybutadiene prepolymer 6.0 trimethylolpropane (additive) 0.06 wetting agent (reaction product 0.30 of equimolar quantities of 12-hydroxystearic acid and tris[2-methylaziridinyl]phosphine oxide) (additive) isophorone diisocyanate (additive) 0.70; ______________________________________ said composite-modified, double-base propellant composition consisting essentially of a casting powder portion in weight percents of the ingredients as follows: ______________________________________ nitrocellulose 16.6 nitroglycerin 6.1 carboranylmethyl propionate 3.7-4.7 ammonium perchlorate (1.0 μm) 32.8 aluminum powder 7.2 aluminum whiskers 2.9 resorcinol 0.7 2-nitrodiphenylamine 1.1 ______________________________________ and a casting solvent portion in weight percents of the ingredients as follows: ______________________________________ nitroglycerin 25.0 triacetin 2.5 2-nitrodiphenylamine 0.3 hexane diisocyanate 0.14 triphenylbismuthine 0.02 ______________________________________ the improvement in burning rate achieved by incorporation of from about 2.9 to about 4.0 weight percent of heat-expandable beads of discrete particles of thermoplastic styrene or its copolymers into the propellant matrix of said composite propellant composition, or substituting said heat-expandable beads for said aluminum whiskers when said selected propellant composition is said composite-modified, double-base propellant composition, said heat expandable beads containing about 5-8% by weight of an expanding or blowing agent that results in bead expansion or rupture during propellant burning when the flame front reaches said heat-expandable bead, said bead expansion or rupture bringing about disruption of the propellant's surface to permit flame penetration into the propellant to thereby achieve a major increase in burning rate of said propellant composition.