Study and evaluation of dispersion of polyhedral oligomeric silsesquioxane and silica filler in polypropylene composites

Various methods were used for evaluation of homogeneity of polypropylene (PP) matrix composites with octakis([n‐octyl]dimethylsiloxy)octasilsesquioxane, octakis([n‐octadecyl]dimethylsiloxy)octasilsesquioxane, and silica (SiO₂) fillers. The filler dispersion was determined on the basis of the results from the wide‐angle X‐ray scattering (WAXS) analysis, from the tests of selected mechanical properties, from scanning electron microscopy (SEM) with energy dispersive X‐ray spectroscopy and from the decomposable entropic descriptor method. The use of different methods allowed to evaluate homogeneity of PP composites on various levels and with different precisions. The dispersion degree was found to be mostly depended on the kind and amount of the filler used. The presence of long n‐alkyl chain substituents in POSS molecules greatly improved the level of filler dispersion in the polymer matrix in comparison to silica which was visually assessed by SEM. The WAXS method revealed the formation of filler aggregates in the PP matrix which influenced the structural characteristic of PP composites and changed the mechanical properties of those materials. However, the decomposable entropic descriptor method provided the possibility of quantitative and the most objective estimation of homogeneity of the obtained composite materials. POLYM. COMPOS., 40:1354–1364, 2019. © 2018 Society of Plastics Engineers