Partial crosslinking of the heterophasic ethylene-propylene copolymer in the solid phase

The influence of radical modification with peroxides under solid phase cond itions on mechanical properties and the morphology of an heterophasic ethyl ene-propylene copolymer (HECO) were investigated. The extent of crosslinkin g and degradation was characterized by the melt flow index and extraction d ata. Influence of modification on dynamic viscoelasticity of HECO was also investigated. The morphology was studied by the transmission electron micro scopy (TEM). Tensil and impact tests were performed on samples of the modif ied HECO. Crosslinking occurred in the dispersed EPR phase of HECO in the i nvestigated peroxide concentration range. The extent of crosslinking and de gradation was dependent on the type of peroxide as a result of the modifica tion 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 a t low peroxide concentrations. Improved impact strength at 23 degrees C was attained. Loss of toughness at -20 degrees C was found probably due to sli ght degradation of PP matrix and due to an inhomogeneous crosslinking of EP R in HECO.