A new approach designed for improving in situ compatibilization of polypropylene/polystyrene blends via reactive extrusion with supercritical CO2 as the processing medium

Abstract

The present work aimed to explore a new approach for more advanced in situ compatibilization through studying the effect of supercritical carbon dioxide (scCO2) as a green processing medium on in situ compatibilization of polypropylene/polystyrene (PP/PS) blends via reactive extrusion. The effectiveness of the in situ compatibilization with scCO2 on the phase dispersion and mechanical properties was studied via comparison with that of the other approaches of thermal blending without scCO2, thermal blending with scCO2 and in situ compatibilization without scCO2. In the in situ compatibilization with scCO2, trimethylolpropane triacrylate (TMPTA) and dibenzoyl peroxide (BPO) were applied as polyfunctional monomer and radical initiator, respectively. Fourier transform infrared spectroscopy (FTIR) was used to confirm the formation of the block and/or graft copolymers (PP-b-PS and/or PP-g-PS) during reactive extrusion and further to study the effect of scCO2 on the yield of the interfacial modifiers. Scanning electron microscopy (SEM) was applied to observe the phase dispersion of the PP/PS blends prepared via different approaches and thus to analyze the functions of scCO2 in improving the phase dispersion in the in situ compatibilization. Impact tests were carried out with samples prepared via different approaches without and with thermal annealing to confirm the effectiveness of in situ compatibilization with scCO2. The results showed that the interfacial modifiers were in situ formed during reactive extrusion, and that the yield was increased with scCO2. It was further found that scCO2 could improve the phase dispersion and thus the mechanical properties of the PP/PS blends prepared via in situ compatibilization through two functions: scCO2-assisted phase dispersion and scCO2-promoted in situ compatibilization. Therefore, the better phase dispersion of the PP/PS blends prepared via in situ compatibilization with scCO2 could be attributed to the two functions of scCO2 as well as a basic thermal blending and a primary in situ compatibilization. Thus, compared to the other approaches, in situ compatibilization with scCO2 has proved to be a more effective approach in improving phase dispersion and enhancing mechanical properties.