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RESEARCH PRODUCT

Recycling of the "light fraction" from municipal post-consumer plastics: Effect of adding wood fibers

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At present the recycling of plastic materials is mostly done using homogeneous polymers. Therefore a separation from a municipal collection of plastic objects is necessary before recycling operations. The easiest way of separation is by flotation in water, i.e. the separation of the different plastics based on the different densities with respect to water. This means that all the plastic materials are separated in a “light fraction” mostly of polypropylene and polyethylene and in a “heavy fraction” mainly of poly(vinyl chloride) (PVC) and poly(ethylene terephthalate). The recycling of the light fraction should, in principle, be easy because of the relative similarity of the chemical structure of the components. The presence of small amounts of polystyrene foam (lighter than water) or of some polymer, such as PVC, or non-polymeric impurities can, however, make the properties of the secondary material quite poor. In this work, the recycling of a light fraction sample has been studied, considering also the effect of the addition of wood fibers, an “environment friendly” filler. Although the similar chemical nature of the two main components, the mechanical properties of the recycled mixture are quite scarce, mainly because of the incompatibility and the possible presence of some heterogeneous particles. The addition of wood fibers (20–40 wt%) leads to a remarkable increase of the elastic modulus while elongation at break and impact strength decrease and the tensile strength remains almost unchanged. Thermomechanical properties are also improved. In order to improve these properties, two functionalized polypropylene samples were used as adhesion promoters. Both polypropylene-grafted maleic anhydride and polypropylene-grafted acrylic acid improve the mechanical properties in particular at very low concentrations. Copyright © 1999 John Wiley & Sons, Ltd.