Curing reaction kinetics of the EHTPB-based PBX binder system and its mechanical properties

Abstract

In this research, differential scanning calorimetry (DSC) was employed to compare the curing reaction kinetics of the epoxidized hydroxyl terminated polybutadiene-isophorone diisocyanate (EHTPB-IPDI) and hydroxyl terminated polybutadiene-isophorone diisocyanate (HTPB-IPDI) binder systems. Glass transition temperature (Tg) and mechanical properties of the EHTPB-IPDI and HTPB-IPDI binder systems were determined using the DSC method and a universal testing machine, respectively. For the EHTPB-IPDI binder system, the change of viscosity during the curing process in the presence of dibutyltin silicate (DBTDL) and tin 2-ethylhexanoate (TECH) catalysts was studied, and the activation energy was estimated. The results show that the activation energies (Ea) of the curing reaction of the EHTPB-IPDI and HTPB-IPDI binder systems are 53.8 and 59.1 kJ·mol−1, respectively. While their average initial curing temperatures of the two systems are 178.2 and 189.5◦C, respectively. The EHTPB-IPDI binder system exhibits a higher reactivity. Compared with the HTPB-IPDI binder system, the Tg of the EHTPB-IPDI binder system is increased by 5◦C. Its tensile strength and tear strength are increased by 12% and 17%, respectively, while its elongation at break is reduced by 10%. Epoxy groups and isocyanates react to form oxazolidinones, thereby improving the mechanical properties and thermal stability of polyurethane materials. These differences indicate that the EHTPB-IPDI binder system has better thermal stability and mechanical properties. During the EHTPB-IPDI binder system’s curing process, the DBTDL catalyst may ensure a higher viscosity growth rate, indicating a better catalytic effect, consistent with the prediction results obtained using the non-isothermal kinetic analysis method.