Flame retardant properties of polycarbonate/irregular polyphenylsilsesquioxane composites

Irregular polyphenylsilsesquioxane (IPPS) was independently synthesized in our laboratory. IPPS mixed with polycarbonate (PC) by the twin-screw extruder to prepare PC/IPPS composites. The flammability of the PC/IPPS composites was characterized by limiting oxygen index (LOI), UL 94 burning rating and Cone calorimeter test. The mechanical properties of PC/IPPS composites, such as tensile strength, flexural strength and modulus, were tested. The thermal properties were analyzed through the thermal gravimetric analysis (TGA). The results show that the LOI value of PC/8% IPPS composite can achieve 35.5% comparing with 26% of pure PC, and UL94 (1.6 mm) can reach V-0 rating. The peak heat release rate (PHRR) decreases from 570.8 kW/m ² to 267.3 kW/m ² in the 8% IPPS loading. The surface of char residues is covered by white silica, which can prevent transfer of the heat and oxygen to PC matrix. The mechanical properties of PC with IPPS loading has a slightly decrease. However, the addition IPPS has no effect on the thermal degradation path of PC matrix.