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

Reactive melt processing of polyethylene (PE) was accomplished at 170 degrees 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 degrees 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 100 g 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 greater than or equal to 170 degrees C. (C) 1997 Elsevier Science Ltd.