ADDED-VALUE OF RECYCLED MIXED PLASTICS THROUGH INTERFACIAL MODIFICATION: EFFECTS OF PROCESSING CONDITIONS ON FINAL PROPERTIES OF MODIFIED MIXED PLASTICS WASTES

摘要

Many problems are associated with reprocessing of plastics wastes. One of the technical problems associated with plastics wastes is their heterogeneous composition. Very often, plastics wastes are a mixture of several polymers which need to be separated in order to assure good properties and quality of recycled polymers. Sometimes it is difficult, costly and in many cases also impossible to acquire a material with a purity comparable to that of a virgin polymeric material when plastic waste is being recovered by mechanical recycling. However, different possibilities of improving the quality of recycled plastics exist. Some of them are technological and some are physical/chemical. Some modifying techniques - like compatibilization - enable us to produce polymeric materials from recycled heterogeneous plastics with much improved profile of mechanical properties. In a wider sense of a word, the compatibilization is any chemical or physical action that results in stabilization (i.e. prevention to separate) of polymer blend's phase morphology. Mostly, the compatibilization is meant a modification method whereby polymer blend morphology can be controlled through the use of block copolymers capable of acting as interfacial agents. Additionally, in many cases such modified heterogeneous recycled plastics can be produced by the usual processing machines. The aim of the paper is to study the influence different processing parameters on the profile of the mechanical properties of compatibilized and noncompatibilized recycled polymer blends prepared from recycled low-density polyethylene (PE-LD) and recycled polystyrene (PS) which represent two of the most widely used commodity plastics. Two different technological routes for the preparation of modified recycled materials were used: compression moulding and injection moulding. In order to optimize final properties of recycled materials we studied the influence of two of such technological parameters: the temperature profile of the heated barrel and cooling rate in the mould. In addition, different modifiers (compatibilizing agent) were added to the recycled materials in order to follow their imapct on the final properties of secondary materials. In some cases a significant improvements in mechanical properties (impact strength, elongation at yield) were obtained. This fact is very important regarding the commercial value of mixed recycled plastics and their applicability.