Crystallization and morphology development in polyethylene–octakis(n-octadecyldimethylsiloxy)octasilsesquioxane nanocomposite blends

The dispersion, morphology and crystallization kinetics of low density polyethylene (LDPE)-octakis(n-octadecyldimethylsiloxy)octasilsesquioxane (POSS) nanocomposite blends was investigated. Novel octakis(dimethylsiloxy) octasilsesquioxane (Q(8)M(8)(H)) molecules were octafunctionalised with octadecyl alkyl-chains (Q(8)C(18)) and blended with 0.25-10 wt% loadings into a commercial LDPE. Time-resolved Small-and Wide-Angle X-ray Scattering (SAXS/WAXS), thermal and microscopy techniques were used to elucidate the POSS dispersal, crystalline morphology and crystallization kinetics of the host polymer. POSS particles dispersed well in the host polymer up to 5% wt loading and acted as nucleating agents without disrupting the crystal lattice of the PE. Above 5% wt loading the POSS aggregated, reduced the bulk crystallinity and hindered the crystallization process. The aggregation of POSS is attributed to increased POSS-POSS interactions whereby the POSS molecules self-assemble in an interdigitated manner. The results were compared with an analogous LDPE-T8C18 POSS cage blend at 10% wt loading. In complete contrast, the T-8 POSS particles disperse well in the host polymer being effective nucleating agents and increased the bulk crystallinity. This may have important implications in the processing of polyolefins where the T-8 system acts to accelerate crystallization whereas the Q(8) system retards it.