Polyethylene/Microgranular Cellulose Composites Prepared by Reactive Extrusion with an Azidotriazine Grafting Agent

High-density polyethylene (PE) plays a central role in polymer composite materials due to its excellent mechanical properties, ease of processing, and low cost. In the quest for more sustainable materials, biosourced fillers like microgranular cellulose (MGC) have emerged as a promising alternative to conventional reinforcements. MGC is particularly attractive because it is mechanically extracted from cotton waste and requires little to no chemical pretreatment. In this study, we harnessed dynamic covalent chemistry to enhance the thermomechanical properties of PE/MGC composites while maintaining mechanical recyclability. Samples were prepared by reactive extrusion of PE and MGC (20 wt %) in the presence of an azidotriazine grafting agent (1 wt %), and the influence of the extrusion conditions on the microstructure and thermomechanical properties was investigated. The resulting materials exhibit a higher Young’s modulus and yield stress than virgin PE, with elongation at break values varying according to the processing conditions. Morphological analysis via scanning electron microscopy, combined with energy-dispersive X-ray spectroscopy and selective cellulose dissolution, revealed how the processing conditions dictate the microstructure and filler dispersion within the PE matrix. The mechanical recyclability of the composites was evaluated, with most thermomechanical properties retained after reprocessing. Composites containing 40 wt % of MGC were also prepared. These materials exhibit a strongly improved Young’s modulus, yield stress, and creep resistance compared to PE, all while incorporating a large proportion of cellulose extracted from cotton waste.