Preparation of polypropylene/sepiolite nanocomposites using supercritical CO2 assisted mixing

Well dispersed polypropylene (PP)/sepiolite clay nanocomposites were prepared successfully using supercritical carbon dioxide (scCO₂) assisted mixing with and without the presence of maleic anhydride grafted polypropylene (PP-g-MA) as compatibilizer. The resulting morphology and polymorphism of nanocomposites were established using X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observations. The mechanical properties of the nanocomposites were investigated and compared with those obtained by a traditional melt compounding method. Our results showed that by using scCO₂ in the process, we were able to obtain better sepiolite dispersions and reduce breakage of sepiolite fibres. Consequently, a significant improvement in the yield stress was observed for the nanocomposites processed in scCO₂ compared to those processed by the traditional melt compounding. XRD data also indicated that the resulting nanocomposites had only α-phase crystallites of PP while the presence of sepiolite could also induce preferred orientation of these α-phase crystallites.