The effect of pyrolysis gaseous and condensed char of PC/PPSQ composite on combustion behavior

Polycarbonate (PC) is flame retarded by polyphenylsilsesquioxane (PPSQ) with a ladder structure. The flame retardant mechanism of PC/PPSQ composite between the gas phase and condensed phase is investigated using a thermo-gravimetric analyzer coupled with Fourier transform infrared spectrometry (TG-FTIR), pyrolysis/gas chromatography and mass spectrometry (Py-GC/MS), cone calorimeter and scanning electron microscope-energy disperse spectroscopy (SEM-EDS). TG-FTIR results indicate that the thermal stability of the PC/PPSQ composite is marginally better than that of PC, and evolving gaseous products during the pyrolysis and infrared analysis, such as CO2, ester groups, aromatic components and isopropyl groups, are found. Py-GC/MS results show that higher concentrations of micromolecule gas products are released from the PC/PPSQ composite, which is beneficial for creating an intumescent char layer. Cone calorimeter tests and temperature variations of the top and bottom char layers indicate that the PC/PPSQ composite and the char layer have a good heat insulation effect. The results of char residues from FTIR indicate that SiO2 is composed of fumed silica which is attached to the internal surface char, white SiO2 is exposed to outside when the char is burned broken and the condensed phase of top char is composed of Si-O-Si and Si-C. The main structure of the bottom char is inorganic carbon. The SEM-EDS analysis indicates that the condensed phase of the char residue structure is composed of three elements, C, O and Si, the content of O and Si is much higher than C.