High-Melt-Strength Recycled High-Density Polyethylene: Evaluation of a Novel Route for Targeting the Polymer Microstructure

The mechanical recycling of thermoplastics (especially of polyolefins) often results in recyclates with inferior properties compared to their virgin counterparts. This phenomenon is mainly due to the modification of the polymer microstructure induced by the degradation processes undergone by the materials during their service life and reprocessing. In this work, a promising route for obtaining high-melt-strength recycled high-density polyethylene (HDPE) is proposed. In particular, the exploited approach involves the utilization of a commercially available additive (i.e., Nexamite^® R305, Nexam Chemical, Lomma, Sweden), which was demonstrated to be capable of driving thermo-mechanical degradation reactions (experienced by HDPE during mechanical recycling) towards the obtainment of a long-chain branched microstructure, thereby enabling the further processing of the recycled material through technologies dominated by elongational flow. The additive-induced alterations of the polymer microstructure were exploited for the formulation of fibers, and the performed tensile characterization showed that the additive-containing material exhibits strikingly improved ductility (namely, elongation at break of 350% for the fibers stretched at a draw ratio of 60) with respect to pristine recycled HDPE. Overall, the obtained results clearly demonstrated the possibility of attaining an effective upcycling of HDPE, which could be exploited for industrially relevant high-added-value applications, hence paving the way for the achievement of full plastic circularity.