Robust propellant liner and interfacial propellant burn rate control

Abstract

A robust polyurethane liner is disclosed for solid propellant rocket motors which is insensitive to large variations in stoichiometry, exhibits increased cohesive strength and, when used in combination with a unique two coat (wet coat) liner process described below, modifies the ballistic properties of the adjacent interfacial propellant layer. The liner compositions include a polymeric binder having a plurality of reactive hydroxyl functional groups and a curing agent having a plurality of reactive isocyanate functional groups. The quantity of binder and curing agent is selected such that the NCO/OH ratio is in the range from 1.5 to 4.5. Diisocyanate curing agents are particularly useful. A bonding agent, such as a polyfunctional aziridine compound, is typically present in the liner composition in an amount ranging from about 3% to about 5%, by weight. An oligomer catalyst is included in the liner composition in an amount ranging from about 15% to about 50%, by weight. Diammonium phosphate ((NH.sub.4).sub.2 HPO.sub.4) functions as an oligomer catalyst and as a ballistic modifier to inhibit propellant burn rate when the liner is cured concurrently with the propellant. A colorant, such as rhodamine B, may optionally be included to assist in determining coverage or thickness of the liner coating.