Study of low concentrations of dicumyl peroxide on the molecular structure modification of LLDPE by reactive extrusion

摘要

The effect of low concentrations of dicumyl peroxide (DCP) on the molecular weight of a linear low density polyethylene (LLDPE) during a reactive extrusion process was studied. The experiments were arranged in a two level factorial design in order to evaluate the effect of peroxide concentration (X-2), temperature zones (X-1) and screw rpm (X-3) on the crosslinking of LLDPE. The melt flow index (MFI) was used as a response variable. It was verified that the thermal properties, crystalline melting temperature (T-m), the heat of fusion (DeltaH(melt)) and the degree of crystallinity (X%) tend to decrease with increase of the peroxide concentration. The crystallization temperature (T-c) increased up to 0.5% w/w peroxide, whereafter the level stays almost constant. In this study, it was also verified through the dynamic rheological data that there was an increase of the complex viscosity and the complex modulus (G' and G"). These results can be an indication that there was an increase of the polymer average molecular weight (M,.) and polydispersity (MWD). The gel content of the samples, however, indicated that a three-dimensional network was negligible in the experimental conditions used. (C) 2004 Elsevier Ltd. All rights reserved.