Comparison between pyrolysis products and condensed phase of polycarbonate/polyhedral oligomericsilsesquioxane composites

Octaphenyl polyhedral oligomeric silsesquioxanes (OPS) and a new novel flame rerardant of polyhedral oligomeric silsesquioxane containing 9, 10-dihydro-9-oxa-10-phoshaphenanthrene -10-oxide (DOPO-POSS) were synthesized in our lab. 4% DOPO-POSS and 6% OPS were mixed with polycarbonate(PC) by a twin-screw extruder to prepare the flame retardant composites. The analysis of pyrolysis product between PC/DOPO-POSS and PC/OPS composites were measured by pyrolysis chromatography-mass spectrometry(Py-GC/MS); FT-IR and SEM-EDS were used to analyze the condensed phase structure and element components of the char residues. The results of Py-GC/MS analysis show that OPS releases amount of gaseous phase of benzene and SiO₂. DOPO-POSS has a more complicated pyrolytic process than OPS, and the main pyrolysis product of DOPO-POSS is DOPO which can reach 26%. The total mass spectrum indicates that PC/DOPO-POSS and PC/OPS composites release amounts of micromolecule gaseous products during the pyrolysis process, and these micromolecule gaseous products swell the char during combustion. In the aspect of condensed phase, the results of FT-IR indicate that the internal char residue structure of PC/DOPO-POSS and PC/OPS are both composed of inorganic carbons. The external char residue structure of PC/DOPO-POSS contain amounts of -P(=O)-O-Si- and a little of Si-O structure. The external char residue structure of PC/OPS contains amounts of Si-O-Si structure and a little of polyaromatic carbons and Si-C structures. The analysis of SEM-EDS indicates that the element content of C is the highest, and then O takes the second place, the content of Si and P is the lowest. In PC/OPS composites, the element content of Si and C is the highest and total mass takes about 92.5%, and the content of C is the lowest.