Effects of filler type and processing apparatus on the properties of the recycled "Light fraction" from municipal post-consumer plastics

Abstract

Plastic waste or scraps are generated from two main sources: industrial wastes and post-consumer wastes. By using the flotation method, generally two fractions are obtained from municipal post-consumer wastes: a light fraction, floating on water, and a heavy fraction. The former is essentially made of low and high density polyethylene - LDPE, HDPE - and polypropylene - PP; the heavy fraction is formed by poly(vinyl chloride) - PVC - and poly(ethylene terephthalate) - PET. In this work, the recycling of a light fraction from municipal post-consumer plastics has been studied, considering also the effect of filler type - glass fibres, calcium carbonate and wood fibres - and processing apparatus - discountinous mixer, single and twin screw extruder - on the properties. Although the similar chemical nature of the two main components, polyethylene and polypropylene of the light fraction, the mechanical properties of the recycled mixture are quite scarce, mainly because of the incompatibility and the possible presence of some heterogeneous particles. The recycling of the light fraction can significantly change the properties of the polymer system because of the thermomechanical stress and of the residence time during processing. The adding of the three fillers type leads to an increase of the thermomechanical and of some of the mechanical properties. The elastic modulus increases with the three fillers; in particular, glass fibres show the best results. Tle effect of the three fillers is quite similar for tensile strength, elongation at break and impact strength. The adding of inert filler strongly improves the rigidity of light fraction from municipal post-consumer plastics. Copyright © 2001 John Wiley and Sons, Ltd.