Ablation and fire-retardant properties of hydroxyl-terminated polybutadiene-based polyurethane- g -polyhedral oligomeric silsesquioxane composites

Abstract

This study examined the ablation and flammability of hydroxyl-terminated polybutadiene-based polyurethane composites grafted by polyhedral oligomeric silsesquioxane (HTPB-based PU-g-POSS) that were prepared by a one-step PU reaction using the HTPB prepolymer, two types of reactive POSS diol, and isophorone diisocyanate. The ablation property was measured using an oxyacetylene torch, and the ablation rate and relative ablation resistivity were evaluated. The results show that POSS molecules incorporated chemically into the HTPB-based PU matrix make a positive contribution to the ablative resistance. POSS molecules in the HTPB-based PU composites exhibited distinct microphase separation, aggregating into a spherical shape on the nanometer scale. This morphology of the POSS domain in the HTPB-based PU matrix leads to the formation of densely accumulated spherical silica (SiO₂) droplets on the top of the ablated surface of materials under thermally oxidative conditions during ablation, resulting in improved ablation resistance compared with pristine HTPB-based PU. This unique SiO₂-forming ability of POSS molecules can also enhance the flame-retardant behavior of the composites, as illustrated by the limited oxygen index and cone calorimeter measurements.