High Impact Polystyrene / Magnesium Hydroxide Halogen-free Flame-retardant Composites Modified And Performance

With the increasing emphasis on the ecological environment, halogen-free flame retardant/polymer composites have been paid much more attentions recently. However, for the poor compatibilities between inorganic flame retardant and organic polymer matrix, the mechanical properties of composites have been deteriorated to achieve an acceptable level of flame retardancy. In order to improve the compatibility between inorganic and organic phases further, surface modifiers have been applied widely.In this thesis, high-impact polystyrene (HIPS) is applied as polymer matrix, and magnesium hydroxide (MH) is used as flame retardant. HIPS/MH composites have been prepared by self-compatibilization technology. At the beginning, a few parts of HIPS have been sulfonated, and the sulfonated HIPS are used as modifier instand of styrene-butadiene-styrene block copolymer (SBS). Both the flame retardancy and mechanical performances of the HIPS/MH composites have been improved effectively. In addition, the effects of the sulfonation degree and the dosage of the macromolecular compatibilizer on the properties of HIPS/MH composites have been studied systematically. Moreover, further characterizations, such as scanning electron microscope (SEM), thermogravimetric analysis (TG), and particle size and particle size distribution analysis, have been carried out to investigate the compatibilization mechanisms. Several interesting results have been drawn:(1) The sulfonation degree is one of the most important structural factors for sulfonated HIPS. It indicates that the mechanical performances of HIPS/MH composites modified by different sulfonated HIPS with various sulfonation degrees have been all improved. The sulfonated HIPS with sulfonation degree around 20-30% bear the best modification effects, therefore the modifiers with the sulfonation degrees neither too low nor too high is beneficial to improve the performances of the composites further. When the sulfonation degree is too low, the MH particles have not been modified adequately; On the other side, when the sulfonation degree is too high, the polarity of sulfonated HIPS is too strong to be compatible well with polymer matrix.(2) In addition, the dosage effects of the compatibilizers on the properties of HIPS/MH composites have been also investigated. The thermal oxidative stabilities of composites modified by sulfonated HIPS as well as the mechanical properties show optimal values only occurred in a proper content around 10%(relative to the weight of MH), but more or less modifiers could not reach to optimal properties. The intrinsic reasons for this phenomenon are found to be ascribed to two opposite effects of surface modifiers:On the one hand, the surface modifiers would improve the adhesion and dispersion of inorganic fillers in polymer matrix and counteract self-aggregation of MH efficiently; On the other hand, with the content of modifiers increase, the particle size of MH turns bigger and its distribution becomes wider, which are both disadvantageous to improve the performances of the composites. So the content of surface modifiers should be controlled in a suitable range.Furthermore, based on the experimental results about mechanical test, thermal stability analysis and surface morphology observation, the HIPS/MH composites modified by sulfonated HIPS show both higher flame retardancy and mechanical properties, but lower cost than that by SBS. Therefore, it has broad application prospects.