Zeolites as effective desiccants to solve hygroscopicity issue of post-consumer mixed recycled polyolefins

The issue addressed in this study concerns the hygroscopicity of post-consumer mixed recycled polyolefins (PCMP). PCMP commonly incorporate polar contaminants, responsible of their moisture sorption and bad smell; as a consequence, it is necessary to dehumidify the recycled material before processing it. This represents a strong technical limitation, since polyolefin converters are not generally equipped with dehumidification plants, so hindering the future circular economy perspectives for these recycled materials. In order to address this issue, in this study we proposed an easy and innovative solution, alternative to drying and based on the use, never considered before, of zeolites as desiccant additives during PCMP extrusion. At this regard, we prepared, on a pilot scale extrusion plant, several material formulations based on undried PCMP loaded with different amounts and types of zeolites, with and without a compatibilizing agent. The obtained systems were submitted to mechanical tensile test to assess the effectiveness and the technological relevance of the proposed strategy with regard to conventional heat drying and a calcium oxide-based desiccant, specially marketed for processing recycled polyolefins. Results showed that the addition of either type of zeolites at 2 wt% loading has an effective desiccant function during PCMP processing and, with respect to heat drying or calcium oxide desiccant, ensures higher strength of the resultant systems (up to ca. 15% and 40%, respectively). Moreover, the use of the compatibilizing agent improves the mechanical performances until they are a little better than those of the heat dried PCMP. Therefore, in a sustainability perspective of the packaging industry, the proposed strategy can offer a tangible contribution to improve the plastic packaging circularity and to reach the EU plastic recycling targets.