Mapping oft the optimal mechanical responses in commercial‐grade HTPB‐based binders

Abstract Alternative binders for composite solid propellants (CSP) have always been a concern. One of the closest alternative to the broadly used military‐grade hydroxyl‐terminated polybutadiene (HTPB) would be its commercial‐grade. Factorial design of experiments (DoE) was applied to optimize the mechanical properties of the binder. Commercial‐grade HTPB was used, in addition to 1,4‐butanediol (BDO) as chain extender, and either isophorone diisocyanate (IPDI) or 4,4’‐methylenedicyclohexyl diisocyanate (H 12 MDI) as curing agents. The effect of simultaneously varying two factors: [NCO]/[OH] molar ratio, and BDO:HTPB mass fraction on the mechanical properties of the binder was evaluated. DoE gave the optimal conditions at 0.68 molar ratio, and 0.71 % BDO:HTPB mass fraction for IPDI; and at 0.66 and 0.57 %, respectively, for H 12 MDI. Higher strength was observed for binders formulated with H 12 MDI. At the optimal conditions, CSP formulated with commercial HTPB showed higher strength than CSP formulated with military HTPB. Moreover, with H 12 MDI higher elongation was observed (28±4 %) when compared to IPDI (19±1%). Thus, the former is a promising diisocyanate for tailoring CSP formulations with commercial‐grade HTPB.