Investigation the effect of NCO/OH ratio, amount and type of curing catayst on the Pot life of HTPB based binder system

The pot life of high-energy composites is one of the most important parameters of their manufacturing process. This is mainly influenced by the pot life of the binder system. In this research, the effect of different amounts of two types of curing catalyst (dibutyltin dilaurate (DBTDL) and triphenyl bismuth (TPB)) and different ratios of NCO / OH (R) on the pot life and physical properties of the polyurethane binder system  based on Hydroxyl-terminated polybutadiene (HTPB) was investigated. By increasing the amount of curing catalyst for both types of catalysts, the viscosity build-up of the binder system measured by the rotation viscometer was intensified. Also, increasing the amount of R from 0.8 to 1 increases the viscosity and crosslink density. Isophorone Diisocyanate (IPDI) binder system shows two distinct steps of increasing viscosity with two different rates, which is attributed to the presence of two different isocyanate groups in the molecular structure of IPDI with different reactivity. In the following, the physical properties and swelling of binder samples were investigated. Based on these results, binders with the highest crosslink density have the lowest swelling. The pot life value increases from R of 1 to 1.1, contrary to expectation, with pot life range value between R of 1 to 0.9. When using the DBTDL catalyst, it is clearly identifiable between different reactivity of two groups IPDI isocyanates, but when used with the TPB curing catalyst, this difference was not observed significantly.