The influence of processing on the mechanical properties and emissions of a recycled polyolefin

Recycled plastics contain volatile compounds from materials degradation as well as from other sources, besides monomer and oligomer residues from the polymerisation process. These volatile compounds cause smell and emissions, which have a negative impact on materials quality. For some applications, e.g. for automotive interior, smell and emissions are critical, thus limiting the use of recyclates there. A degassing step in a co-rotating twin screw extruder is a possible way to reduce these emissions. Therefore, the aim of this work was to investigate the influence of melt processing on the mechanical properties and the emissions of a recycled post-consumer polyolefin mixture. Different screw configurations, process parameters and degassing variations, also with additives to improve degassing, are used. The influence of the process on the emissions was tested by headspace gas chromatography (VDA 277). Also, tensile and impact properties were recorded to see if there is an influence of the processing. Oxygen induction time was evaluated to check for the degradation of the stabilizer during the process. These results were compared with the ones for virgin polypropylene. The first results show that the emissions can be reduced to one third of the untreated recyclate with the degassing process. The sum of the emissions and mechanical properties show some dependence on different screw configurations, process parameters and degassing methods. Further steps are to investigate the emission testing method, especially the influence of sample preparation and test parameters, more in detail and to validate these results.