The study of char forming on OPS/PC and DOPO-POSS/PC composites

Polyhedral oligomeric octaphenyl silsesquioxane (OPS) and polyhedral oligomeric silsesquioxane containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene- 10-oxide (DOPO-POSS) with polycarbonate (PC) were each prepared by twin screw extrusion. Their flammability was studied by cone calorimetry under different heat fluxes (35 and 50 kW/m²). In the cone calorimeter testing, thermocouples were used to measure the temperature at the top and bottom of the composites. Compared to the DOPO-POSS/PC composite, the char layer of the OPS/PC composite is better for preventing heat transfer, the temperature change indicates that OPS/PC composite has a longer period of char formation, and the organization of their char materials are different. The DOPO-POSS/PC composite has a harder char layer than the OPS/PC composite, but the OPS/PC composite char layer is more compact. The char layer macrostructure was studied with scanning electron microscopy (SEM) and EDS, which indicated that there are many bubbles and pores in the DOPO-POSS/PC composite. EDS showed that there was some Si content in the exterior and interior char for the DOPO-POSS/PC composite; there is a greater Si content in the exterior OPS/PC char residue than in the interior. The storage modulus of OPS/PC composite was higher than the PC control and DOPO-POSS/PC composite at low frequencies. The values of η* of the OPS/PC composite were higher than the PC control and DOPO-POSS/PC composite at low frequencies; also, the PC control exhibits a quasi-Newtonian regime, but the OPS/PC and DOPO-POSS/PC composites exhibit typical shear-thinning behavior.