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 CO_2, 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.