Study of polyethylene nanocomposites with polyhedral oligomeric silsesquioxane nanofillers—from structural characteristics to mechanical properties and processability

High‐density polyethylene (HDPE) and low‐density polyethylene (LDPE) nanocomposites filled with octakis({alkyl}dimethylsiloxy)octasilsesquioxanes (POSS) were prepared by the melt blending method. The effects of the structure and the content of POSS nanofillers on free‐volume properties and structural characteristics of nanocomposites were investigated by the positron annihilation lifetime spectroscopy (PALS) and X‐ray diffraction methods: wide‐angle X‐ray scattering (WAXS) and small‐angle X‐ray scattering (SAXS). Incorporation of POSS nanofillers into polyethylene matrices modified the arrangement of the polymer chains and affected the size and number of free‐volume holes in nanocomposites. The presence of POSS molecules influenced also the crystallinity of nanocomposites because of the increased volume occupied by spherulites in polymers. The extent of changes in the structural characteristics of the POSS‐containing nanocomposites was found dependent on the type of the polymeric matrix as well as on the structure and content of the POSS nanofillers used. Incorporation of the POSS nanofiller into the polyethylene matrix increased the mass flow rate values significantly, thus the POSS could be considered as a plasticizer. Moreover, the compositions of nanocomposites strongly affected their mechanical properties which were mostly dependent on the compatibility between the polymer and the nanofiller, and on the ability of the POSS to aggregate. POLYM. COMPOS., 40:E350–E364, 2019. © 2017 Society of Plastics Engineers