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

Abstract

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

Functionalized siloxane‐silsesquioxane resins and polypropylene‐based composites: Morphological, structural, thermal, and mechanical properties

“…The presence of the S4SQ resins in the PP caused the significant increase in the sizes of the α‐ and β ‐form crystallites of PP as compared with neat PP. Similar findings were described for PP/POSS composites in our previous work . All the observed transformations in the crystalline structure of PP in the composites could be explained by the limited mobility and local ordering of PP chains as a result of the presence of the S4SQ resins in the PP matrix.…”

“…Interestingly, the decrease in the χ WAXS values was smaller in the case of the composites which contained S4SQ‐18, probably due to a more homogenous dispersion of the filler in the PP matrix, related to the S4SQ‐H and S4SQ‐8 resins. The similar effect was observed for PP composites filled with silsesquioxanes and silica fillers .…”

“… demonstrated for PP/POSS composites, that the presence of long alkyl substituents in the octakis(alkyl)octasilsesquioxane molecules enhanced filler dispersion. A beneficial effect of long alkyl‐chain substituted silsesquioxane fillers in the polyolefin matrix was also described by other authors .…”

“… in the case of the PP matrix composites which contained the SiOPh. Small shifts towards lower angles, in the positions of the Bragg reflections, may be related to a small increase in the distance between the lattice plane, and thus a slight decrease in the density of crystals of the polymer . In turn, the intensity of the diffraction peak associated with the β ‐form crystals was greatly decreased after incorporation of the S4SQ resins into the PP matrix (Fig.…”

“… for non‐functionalized siloxane‐silsesquioxane resins. Thus, it might be concluded that siloxane‐silsesquioxane resins are more similar to silica than to the POSS compounds .…”