Influence of octyl substituted octakis(dimethylsiloxy)octasilsesquioxane on the morphology and thermal and mechanical properties of low density polyethylene

What is it about?

Low density polyethylene (LDPE) was melt blended with octyl substituted POSS (AS8) prepared in high yield by hydrosilylation of octene with octakis(hydrodimethylsiloxy)octasilsesquioxane. Two procedures were used to incorporate AS8 into LDPE at nanolevel and their efficiency was investigated by X-ray diffraction (XRD), scanning electron microscopy, atomic force microscopy (AFM), differential scanning calorimetry, thermogravimetry and mechanical characterization. A slight increase of crystallite mean dimensions was observed by XRD in both types of LDPE-AS8 composites compared with neat LDPE. Better AS8 dispersion was observed by AFM in the composite prepared by the first procedure and the increase of both tensile strength and elongation at break in this composite confirmed the nanolevel dispersion and interface improvement in this case. AS8 influence in the final stages of polyethylene fracture was illustrated by AFM of elongated tensile specimens and a new mechanism of AS8 action was suggested. An interesting behavior consisting of simultaneous improvement of elastic modulus, strength and ductility was detected in the low range of polyhedral oligomeric silsesquioxane concentration in LDPE (0.5 wt%).

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Why is it important?

We found that the addition of octa-octyl substituted POSS significantly enhanced the mechanical properties of polyethylene especially in the low range of POSS concentration. The simultaneous improvement in modulus, strength and ductility of a nanocomposite is rarely reported and it is of great interest for both scientific and technological purposes. A thermal and morphological study of composites with 8 wt% POSS allowed selection of the proper preparation method although the best mechanical properties were obtained for composites with 0.5–3 wt% POSS.