New thermoplastic vulcanizate, composed of polypropylene and ethylene–vinyl acetate copolymer crosslinked by tetrapropoxysilane: evolution of the blend morphology with respect to the crosslinking reaction conversion

Abstract

AbstractA thermoplastic vulcanizate (TPV) is tailored by a dynamic vulcanization process. TPVs can be processed as thermoplastics and have properties similar to conventional vulcanized rubbers. The main objective of our recent works was to tailor, by using the reactive extrusion process, a new TPV composed of polypropylene homopolymer (PP) as thermoplastic phase and ethylene–vinyl acetate copolymer (EVA) as elastomer phase, which is crosslinked by tetrapropoxysilane (TPOS) as crosslinking agent in the presence of dibutyl tin oxide (DBTO) as catalyst. Crosslinking is carried out through a transesterification reaction between the ester groups of EVA and the alkoxysilane groups of TPOS. This exchange reaction is catalyzed by DBTO at temperatures above 100 °C. The main advantage of this chemistry that it is non‐radical, and so prevent the degradation of PP, in comparison with crosslinking reactions using peroxides as initiators.Different reactive blends were prepared in the internal mixer of a Haake Plasticorder. In order to know how the crosslinking reaction has advanced, the EVA gel content and the volume swelling rate of the blend were measured. The aim of this study was to get a better understanding of the dispersion mechanism of EVA in the major phase during its dynamic vulcanization in the presence of PP in the minor phase. This paper deals with the correlation that exists between the evolution of the two‐phase blend morphology and the extent of the crosslinking reaction on the elastomer phase during the elaboration of a TPV. In particular, we showed that the correlation was almost the same for the elaboration of the TPV in the internal mixer of the Haake Plasticorder (discontinuous process) and in a twin‐screw extruder (continuous process). Copyright © 2004 Society of Chemical Industry