Studies on Gum Stock Using Different Bicurative Systems to Achieve Optimum Pot Life and Mechanical Properties for Composite Propellant Formulations

摘要

Toluene diisocyanate (TDI) is preferred curative for HTPB/AP/AI system, however, pot life has always been a concern along with mechanical properties. Because of this, isophorone diisocyanate (IPDI) is considered over TDI for its low reactivity but high temperature curing causes thermal stress. To avoid above mentioned problems related to TDI and IPDI, a systematic gum stock study based on HTPB has been carried out by selecting different curatives like TDI, DDI, MDI, HMDI, H12MDI and IPDI in bicuratives form in various proportion and evaluated their different properties. The data reveal that end of mix viscosity for bicuratives based on DDI/HMDI, H12MDI, IPDI; TDI/HMDI, H12MDI, IPDI and MDI/HMDI, H12MDI, IPDI are 0.62, 0.81, 0.99, 1.05, 1.11, 1.32, 1.35, 1.36 and 1.38 Pa s, respectively, while pot life for the same bicuratives are found to be 235, 230, 235, 120, 140, 170, 55, 55 and 60 minutes. The shore hardness A for bicuratives based on DDI are 0.10 to 0.20 while bicuratives based on TDI and MDI showed hardness from 9.35-16.27 and 18.56-22.05, respectively. The mechanical properties data reveal that DDI based bicuratives show poor tensile strength, E-modulus and higher elongation while bicuratives based on TDI and MDI demonstrated nominal values. Based on above findings, further bicurative ratios were varied from 1:1 to 1:3 and 3:1 and their findings reveal that TDI/IPDI (70/30) demonstrated optimum viscosity, pot life, shore hardness and mechanical properties.