Improvements in the Properties of Mechanically Recycled Thermoplastics

It is difficult, costly and in many cases also impossible to acquire a material with a purity comparable to that of a virgin material when plastic waste is being recovered by mechanical recycling. Processing and reprocessing initiate degradation of the plastic, which severely reduces the life-time of recycled plastics. This article summarizes recent advances in studies of the compatibility of mechanically recycled polymeric materials. Two grades (amorphous and crystalline) of EPDM were evaluated as impact modifiers in order to upgrade recycled HDPE. The EPDM elastomers improved the tensile impact strength and elongation at yield. The reduced impact strength and elongation caused by up to 10% PS or PET could be compensated for by adding an amount of amorphous EPDM equal to half the weight of HDPE containing low levels of other polymer. The mechanical compatibility between the most common polymer types, such as ABS, polypropylene, polyethylene and polystyrene is reviewed and complemented by new, previously unpublished results. The mineral-filled PP yields at lower elongations and stress-levels when contaminated with ABS, but the ultimate properties are not severely affected. Some contamination by ABS in polypropylene is tolerable whereas ABS shifts from ductile to brittle failure modes when contaminated with only 6% polypropylene. A computer program for response surface methodology (RSM) is presented and the mechanical compatibility of polyethylene and propylene have been evaluated.