Creep Behaviour of High-Density Polyethylene – Carbon Black Composites

TTAINA, MATTEO; PEGORETTI, ALESSANDRO; PENATI, AMABILE; BARBOSA, SILVIA ELENA

Budapest, Hungría

Simposio; 3rd China-Europe Symposium: Processing and Properties of Reinforced Polymers; 2007

Budapest University of Technology and Economics

In this work the viscoelastic properties of high density polyethylene (HDPE) – carbon black (CB) composites were investigated. In particular, HDPE-CB composites were prepared with 2 wt% of two types of CBs having surface areas of 226 m2/g (CB1) and 1353 m2/g (CB2), respectively. All the investigated materials were melt compounded in a corotating intermeshing twin screw extruder. Three consecutive extrusions were performed in order to improve the filler dispersion and to investigate the corresponding effects on the creep behaviour. In any case, the creep compliance of the HDPE-CB composites resulted to be lower than that of the corresponding unfilled HDPE matrix. In particular, the creep resistance improved as CB surface area increased. As the number of consecutive extrusions increased the creep compliance of the HDPE matrix increases due to thermal induced molecular degradation. For the HDPE-CB composites this effect progressively diminished as the CB dimensions decreased, eventually disappearing for CB2. Transmission electron microscopy (TEM) observations of HDPE-CB composites indicated an improved filler dispersion after repeated extrusions. The creep data, collected at various stress and temperatures, were treated accordingly to a time-temperature reduction scheme in order to obtain creep compliance master curves. These curves evidenced better long term creep behaviour of the HDPE-CB composites over the unfilled matrix.