Polycarbonate composites flame-retarded by polyphenylsilsesquioxane of ladder structure

Polyphenylsilsesquioxane (PPSQ) of ladder structure synthesized in laboratory was incorporated into polycarbonate (PC) by means of a twin-screw extruder. Scanning electron microscopy (SEM) observations showed that spherical PPSQ particles of size 0.5-1.5 μm dispersed homogeneously in PC. The incorporation of PPSQ into PC improved the elongation at break and flexural strength. Thermal gravimetric analysis and Fourier transform infrared spectroscopy revealed that PPSQ made the initial thermal decomposition of PC happen fast. The early cleavages of C-C and C-O bonds in the PC chains induced crosslinking reaction in the condensed phase char. According to the cone calorimetry (CONE) tests, loading of 8 wt % PPSQ reduced the peak heat release rate of PC composites from 570 to 153 kW/m ². The chars obtained after CONE testing of PC/PPSQ composites showed continuous, smooth, flaky, and cascading char and SiO ₂ ceramic layer on the top. These indicated the good flame retardancy of PC/PPSQ, that is the attainment of a UL-94 rating of V-0 (1.6 mm), and limiting oxygen index of 42.0% when PPSQ was in 8 wt % in PC.