MODIFICATION OF PROPYLENE-ETHYLENE COPOLYMERS BY REACTIVE EXTRUSION

The rheological properties of commercial propylene-ethylene copolymers were modified by reactive extrusion. A dialkyl peroxide was used as i nitiator of the controlled degradation reaction of the starting polyme rs. The experiments were carried out in a twin screw extruder at diffe rent peroxide concentrations, temperatures, and screw speeds. Gel perm eation chromatography was used to estimate the molecular weight distri bution of the original and modified copolymers. It has been observed t hat the estimated molecular weight of the copolymers tends to decrease with the increase in peroxide concentration at all extrusion conditio ns studied. The linear viscoelastic properties of all the polymers wer e evaluated at different temperatures and frequencies in a rotational rheometer. Both the viscous and the elastic properties decrease with a ugmenting peroxide concentration. The rheological behavior of the mate rials is strongly affected by the global ethylene content of the copol ymers. The scanning electron microscopy study did not reveal a signifi cant difference between the morphology of the unmodified and the modif ied blends for a given composition of the original copolymers. In all the cases the microstructure is composed of a finely dispersed phase o f ethylene-propylene copolymer within a continuous polypropylene phase .