Crystallization and morphology development in polyethylene

The dispersion, morphology and crystallization kinetics of low density polyethylene (LDPE) octakis(noctadecyldimethylsiloxy)octasilsesquioxane (POSS) nanocomposite blends was investigated. Novel octakis(dimethylsiloxy)octasilsesquioxane (Q8M8) molecules were octafunctionalised with octadecyl alkyl-chains (Q8C18) and blended with 0.25-10 wt% loadings into a commercial LDPE. Time-resolved Smalland 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 PE. Above 5% wt loading the POSS aggregated, reduced the bulk crystallinity and hindered the crystallization process. The aggregati on 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 T8 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 T8 system acts to accelerate crystallization whereas the Q 8 system retards it.