Tetrachloro Phthalic Anhydride Based Chloropolyesters for Inhibition of Double Base Rocket Propellants

Abstract

The choice of inhibiting materials for double base and composite modified double base rocket propellants has always been a difficult problem because of the presence of nitroglycerine in these propellants and its subsequent migration from the propellant towards the inhibitor. The inhibition of double base rocket propellants with unsaturated polyesters has become popular in recent years, but they usually suffer from the drawback of high nitroglycerine absorption. This may be considerably lowered by exploiting the concept of introduction of electron acceptance sites in one of the components used for the synthesis of unsaturated polyesters. Chloropolyester-1 (CP-1) based on tetrachlorophthalic anhydride (TCPAn), propylene glycol (PG) and maleic anhydride (MAn) and chloropolyester-2 (CP-2) based on TCPAn,  polyethylene glycol mol. wt. 200 (PEG-200) and MAn have been synthesised and characterised for ge ltime, exotherm peak temperature, tensile strength, % elongation, bond strength, water absorption, nitroglycerine absorption, heat resistance and flame retardance. The blends of CP-1 and CP-2 designated as CPB-2 (CP-1 : CP-2 : : 20 : 80), CPB-4 CPB-6 and CPB-8 have also been formulated and characterised for these properties. Based on the data for various characteristics, CPB-4 has been selected for inhibition and static evaluation of rocket propellants. The double base rocket propellant sustainers containing 2-NDPA have been inhibited with CPB-4 without the application of any barrier coat and statically fired at ambient, cold (-40°C) and hot (+5O°C) temperatures after conditioning. The pressure-time profiles were found to be smooth and flat in all cases, inferring that the CPB-4 inhibition system (without application of any barrier coat) is working satisfactorily.