Lewis acidic polypropylene for compatibilization of polypropylene/microsilica composites

Abstract

Polypropylene (PP) was compounded with submicron size silica filler particles (microsilica, μSi) up to 30 wt-%. In addition, three external compatibilizers, with characteristic functionalities, were studied to examine their influence in the mechanical properties of the PP/μSi composites. As a result, the modulus of the composite increased while the other tensile values deteriorated in correlation with increased filler concentration. The addition of an external compatibilizer reduced this deterioration, but the reduction was dependent on the type of the compatibilizer used. The influence of an acid functionalized compatibilizer was unsubstantial while the fluorosilane and the Lewis acidic phenylsilane functionalized polypropylenes acted as effective compatibilizers. In addition to examining the tensile properties, the toughness of the composites was evaluated as well. The microsilica filler was found to act as toughening agent since the Brittle-to-Ductile transition point of the composite increased by 2-3 orders of magnitude at high filler concentrations. However, this increase in the toughness was rapidly lost when an effective compatibilizer was used to bind the filler with the matrix. This observation was consistent with the common understanding of the filler toughening mechanism, where particle-matrix debonding is a prerequisite for facilitating the plastic stretch of the polymer ligaments between filler particles. In our case, however, the few filler aggregates in the polymer matrix also played a crucial role. While in uncompatibilized composites the filler aggregates remained passive (could not be seen at the fracture surface), the addition of an effective compatibilizer activated these aggregates to promote crack initiation and/or propagation. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers