Investigation of swelling degree of polypropylene beads with monomers and blowing agents

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Abstract The swelling step of polymer particles or beads with blowing agents and monomers is one of the factors that directly affect the performance properties of expandable core–shell particles, including morphology, composition, and expansion degree. In this regard, the present work investigated the effect of swelling agents on polypropylene (PP) beads. Swelling agents were used to perform swelling tests in both bulk and suspension media at different temperatures and stirring rates. Additionally, a mass transfer model was implemented to predict the swelling degree at the analyzed experimental conditions. The obtained results indicated the important effect of temperature on swelling in both bulk and suspension tests. Among the investigated swelling agents, higher rates of PP beads swelling were observed when styrene was employed (~80 wt%), when compared to methyl methacrylate (~20 wt%), vinyl acetate (~9 wt%), and acrylonitrile (~6 wt%). Moreover, it seems that the stirring rate does not exert a considerable influence on the swelling rates, indicating that swelling is controlled by thermodynamic constraints and particle properties. Finally, experimental results showed that the final saturation concentration of the swelling agent can be reached before 1 hour of swelling, indicating that the swelling kinetics can be much faster than the polymerization kinetics. Highlights The effects of non‐conventional swelling agents on PP were investigated. The swelling presented a fast dynamic behavior. The swelling dynamics was controlled by the solubility of the swelling agent. The highest swelling degree was obtained with styrene.

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