One-step reactive processing of low density polyethylene and octavinyl polyhedral oligomeric silsesquioxane

Abstract

Polyhedral oligomeric silsesquioxane (POSS) are an innovative class of organosilicon compounds suitable for formulation of advanced organic-inorganic hybrid materials. Nanocomposites based POSS found application mostly in high-temperature resistance and fire-resistance materials. POSS are characterized by a three dimensional cage-like structure, made of Si-O bonds, with different organic groups directly linked to the Si atoms of the cage structure. The organic groups can be designed to facilitate the dispersion of the nanoparticle itself in the polymer matrix or also to react with the polymer chain. This work focuses on the possibility to obtain crosslinking of polyethylene using octavinyl-POSS as crosslinker in a simple one-step melt blending process. There are many efforts to find strategies to overcome the shortcomings resulting from the pratical use of peroxide to crosslink matrices. Octavinyl-POSS, bearing eight vinyl groups, is suitable to form chemical bonds with the polyethylene chains through a radical initiated reaction. A small amount of peroxide initiator, Dicumyl Peroxide (DCP) or none was used during the blending process. The different systems were investigated through differential calorimetry, infrared spectroscopy, electron microscopy, soxhlet extraction, rheological and mechanical analysis. The results show that DCP is able to trigger the POSS crosslinking and grafting reaction however, even in the absence of peroxide, all hybrid materials are characterized by a crosslinked structure and exhibit a solid-like rheological behavior. Moreover the effect of a cure process on the materials was investigated: in DCP containing systems the crosslinking process appears to continue although the physically dispersed (not- reacted) POSS molecules tend to form agglomerates.