Nova Metodologia para a Produção de Termoplástico Vulcanizado à base de NBR/PS através da Polimerização In Situ do Estireno no Látex

Abstract

This thesis presents the main objective to develop a process to obtain the nitrile rubber/polystyrene blend (NBR/PS) by the polymerization of styrene monomer into the NBR rubber latex. In this process, the polymerization of styrene monomer occurs simultaneously with the crosslinking of the nitrile rubber (NBR), obtaining a blend with a thermoplastic vulcanizate characteristics. The benzoyl peroxide (BPO) was used as a polymerization initiator and also as crosslinking agent to NBR phase. To conduct this study, we evaluated the effect of the two conditions of processing on the polymerization reaction: stirring and amount of emulsifier. The stability of the reaction was evaluated by the visual identication of precipitation of polymers during processing. The preliminary evaluation of the polymerization reaction of the polystyrene was performed by the infrared spectroscopy (FTIR) which confirmed the presence of PS in the mixture. Using solvent extraction experiments, we found that, under the conditions studied, the best results in terms of reaction conversion, polymerization of styrene, were obtained with low stirring and high amount of emulsifier (400 rpm and 0.896g of emulsifier). Analyzing the glass transition temperature (Tg), using the differential scanning calorimetry technique (DSC), it was found TPV-C contains the highest amount of polystyrene. The mechanical property results showed a decreased the tensile strength and an increase the deformation at break with addition of 5% TPV-C in the NBR/PS blend. The results rheometry using a rubber processing analyzer (RPA) showed that G' and G'' increased with the sweep frequency. The highest values of G' and G'' were observed for TPV-C blend, due to the greater amount of PS. The same result was observed by analyzing the behavior of elastic modulus (G') with strain. Analysis of the micrographs of TPVs, using scanning electron microscopy (MEV), showed the presence of the PS phase, confirming the polymerization reaction. Furthermore, the micrograph also revealed that the polystyrene is dispersed in the NBR phase.