Investigation of the Gum Stock Behavior of Polyurethane Crosslinking Matrix by Adding Triol Diol Mixtures for the Application of Composite Solid Rocket Propellants

The addition of some advanced additives to improve the mechanical properties of polyurethane (PU) polymeric matrix, which acts as a binder system in composite solid rocket propellants (CSRPs), is a target for the energetic materials researchers. In this investigation, 45 compositions of different crosslinked PU matrices were produced to demonstrate the effect of adding crosslinking mixture (CM) on the mechanical capabilities of polyurethane gum stock. The crosslinking mixture (CM) is composed of a triol crosslinker, trimethylolpropane (TMP), and a chain extender, 1,4-butanediol (BD). For comparison, traditional PU samples without crosslinking additives were formulated. As a prepolymer, HTPB was used with a curing agent (HMDI). The research was carried out with different ratios of TMP to BD, different curing ratios (NCO/OH=0.7, 0.9, and 1.1), and crosslinking mixture contents in the range of 0-5 wt.%. The mechanical characteristics of all the cured formulations were measured. It was demonstrated that changing the ratio of TMP to BD has a significant impact on the mechanical performance causing a wide range of elongation and strength qualities. Increasing the wt.% of triol crosslinker in the sample enhanced the tensile strength, whereas the strain has been decreased. The addition of diol chain extender increased the strain rate of the samples. The mechanical parameters were adjusted simply by employing the crosslinking ingredients to get exceptional mechanical characteristics at each NCO/OH curing ratios. Also it was concluded that PU samples of curing ratio (NCO/OH= 0.7-0.9) with TMP:BD (1:1) showed a promising results and could be used according to the requirements of the rocket system designers