Thermal Degradation, Flame Retardant Properties Of Polycarbonate/Polyhedral Oligomeric Silsesquioxane Composites

Organosilicon is one kind of environmental friendly flame retardant. The thermal degradation and combustion products of organosilicon after introduced into the polymers are SiO2 and other silicon-containing compounds, which are almost all environmentally friendly. Moreover, low concentration of smoke and toxic gas will be released during the combustion of silicon-containing polymers, and the propagation of flame is slow.Bisphenol A polycarbonate (PC) is one of the most widely used engineering thermoplastics in the family of polycarbonate due to excellent properties, such as transparency, high mechanical strength, good thermal stability and flame retardancy. PC shows a V-2 rating in the UL-94 test because PC is a naturally high charring polymer, but strict flame retardant performance is often required. Many academic and industrial researchers have participated in the study of flame retardancy of PC and its blends.The newly progress about flame retardancy of PC and the flame retardants used were reviewed in this dissertation based on the investigation of a large amount of literatures. Three series of flame retardant PC hybrids were prepared based on bisphenol A polycarbonate (PC), trisilanolphenyl-polyhedral oligomeric silsesquioxane (TPOSS) and oligomeric bisphenyl A bis(diphenyl phosphate) (BDP) by melt blending method. The thermal stability and flame retardant properties of the hybrids were investigated. The flame retardant mechanism of the silicon and synergistic effects and flame-retardant mechanism of the combination of silicon and phosphorus have been discussed in the paper in detail. Moreover, the fire hazards of the hybrids are all investigated.The paper is mainly divided into three parts:1. Investigation of transmission electronic microscopy and Fourier transform infrared spectroscopy confirms that the nanoscale TPOSS particles were well dispersed in the PC matrix and there is no chemical reaction between the TPOSS particles and PC matrix during the melt blending. The thermal degradation behaviors of the PC/TPOSS hybrids were investigated. The presence of TPOSS significantly affects the thermal degradation process of PC. The combustion behaviors of the hybrids were evaluated by cone calorimetry experiments. The addition of TPOSS significantly decreased the value of peak heat release rate of the hybrids. Moreover, the addition of TPOSS at 2 wt% leads to the maximum decrease of the PHRR. And scanning electron microscopy and X-ray photoelectron spectroscopy were used to explore the char residues of the pure PC and the hybrids. The incorporation of TPOSS retards the oxidation of char residue and enhances the intensity and thermal oxidative stability of the char layer which builds up on the surface of the burning polymer.2. The thermal stability and the flame retardant properties of the PC/BDP and PC/TPOSS/BDP hybrids were investigated. The addition of TPOSS and BDP significantly affect the thermal degradation and combustion behaviors. The results indicated that combination TPOSS with BDP in the appropriate ratio can enhance the thermal stability of the PC matrix under inert and air atmosphere. The ignition of the PC/BDP series hybrids is retarded, but the introduction of TPOSS induces the early ignition of the hybrids. The synergistic effect of BDP and TPOSS significantly decreased the value of peak heat release rate of the hybrids; the addition of 2wt% TPOSS and 3wt% BDP leads to the maximum decrease of the PHRR. The char residues of the pure PC and several hybrids were explored by the scan electronic microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). SiO2 reacts with phosphate resided in char layer to yield silico-phosphate, which can stabilize phosphorus species and char layer. The presence of SiO2 can further enhance the viscosity and thermal oxidative stability of the char layer containing phosphorous which builds up on the surface of the burning polymer, insulates the heat transformation and the dispersion of oxygen into underlying polymeric substrate to prevent thermo-oxidative reactions, and prevents the release of volatile products of underlying polymeric substrate from the matrix.3. The heat release rates of these three series of PC hybrids were investigated by both cone calorimetry and a newly developed method, micro-scale combustion calorimetry (MCC). The heat hazards of these hybrids were evaluated, too. The introduction of TPOSS significantly decreased the PHRR of the PC/TPOSS hybrids under both high and low heat irradiation; and it also significantly decreased the THR under low irradiation. The addition of BDP decreased the PHRR and THR of the PC/BDP hybrids under both high and low heat irradiation; and it also retarded the ignition of the PC/BDP hybrids. Combination of both BDP and TPOSS further decreased the PHRR of the PC/BDP/TPOSS hybrids. BDP retarded the effect of TPOSS with the early ignition of the PC matrix.