PARTIAL CROSSLINKING OF THE HETEROPHASIC ETHYLENE-PROPYLENE COPOLYMER IN THE SOLID PHASE

Abstract

The influence of radical modification with peroxides under solid phase conditions on mechanical properties and the morphology of an heterophasic ethylene-propylene copolymer (HECO) were investigated. The extent of crosslinking and degradation was characterized by the melt flow index and extraction data. Influence of modification on dynamic viscoelasticity of HECO was also investigated. The morphology was studied by the transmission electron microscopy (TEM). Tensil and impact tests were performed on samples of the modified HECO. Crosslinking occurred in the dispersed EPR phase of HECO in the investigated peroxide concentration range. The extent of crosslinking and degradation was dependent on the type of peroxide as a result of the modification in the melt. The modification with higher peroxide concentrations led to the morphology close to the one of the unmodified HECO powder before and also after the extrusion step. The elongation at break of HECO increased at low peroxide concentrations. Improved impact strength at 23°C was attained. Loss of toughness at −20°C was found probably due to slight degradation of PP matrix and due to an inhomogeneous crosslinking of EPR in HECO.