Reactive melt processing of polyethylene: effect of peroxide action on polymer structure, melt rheology and relaxation behaviour

Abstract

Reactive melt processing of polyethylene (PE) was accomplished at 170°C under the influence of two different doses (0.75 and 1.25 mmol per 100 g PE) of dicumyl peroxide (DCP). The effect of peroxide action on melt rheology of PE at 160, 180 and 190°C was studied by a constant shear rate plate and cone viscometer. Peroxide action led to establishment of a mild degree of crosslinkages in PE and hence to enhancement of its melt viscosity, the effect being higher for use of a higher DCP dose. The melts of PE and modified PE showed pseudoplastic flow behaviour. The pseudoplastic character, however was less pronounced at higher rates of shear and at a relatively low temperature. Use of a low dose of DCP (0.75 mmol per 100 g PE) modified the polymer marginally, causing little or only marginal changes in relaxation time and shear modulus, while a higher DCP dose (1.25 mmol per 100g PE) incorporated significant changes in the polymer structure due to establishment of more than a critical degree of peroxide induced crosslinkages, thereby causing a substantial enhancement in the shear modulus and a drop in relaxation time. Odd effects of temperature on viscoelastic character are also interpreted on the basis of total dissolution of residual crystalline orientations in PE melts at ≥ 170°C.