article

Abstract

Polypropylenes (PP) with linear chains and high isotacticity, such as made with metallocene catalysts, show low melt strength in spinning flow. This results in poor properties during processes such as film blowing, blow molding and foaming. This low melt strength is connected to the low elongational viscosity and the absence of sufficient strain hardening. To improve the extensional properties of commercial PP a modification of its molecular structure is employed in the present paper by use of reactive extrusion with specially chosen peroxy-dicarbonates (manufactured by Akzo-Nobel Chemicals). Several types of peroxides at different quantities were used and the reaction took place in an extruder. They were found to result in a few long chain branches introduced by a small extent of crosslinking of the polypropylene chains induced by the peroxide. The modified materials had remarkably higher melt strength accompanied with a limited increase of the shear viscosity. The elasticity of the melts increased as seen both in dynamic shear measurements and in the increase of strain hardening in uniaxial elongation.

polymer 42[25], 10035-10043 , 2001

The influence of peroxydicarbonate modification on the extensional properties of polypropylene