Upcycling Plastic Waste into Tough, Fully Recyclable Composites*

Plastics, with their low cost, offer significant societal benefits, including applications in medicine, food preservation, and fuel efficiency. However, the widespread use of plastics has led to a pressing waste management issue. Traditional recycling methods face challenges in collecting and reusing post-consumer plastics. We propose an innovative approach that enables direct reprocessing of waste materials into durable composites via cold sintering. This process consolidates inorganic powders at lower temperatures than conventional sintering, making it compatible with plastics. Our method circumvents many costly steps associated with advanced recycling. We create structural materials from plastic waste (polypropylene, PP) and construction waste (gypsum) through cold sintering, resulting in inorganic-matrix composites with significantly improved tensile strength and toughness compared to neat gypsum. X-ray Computed Tomography analysis reveals critical mesoscale structures enhancing mechanical properties. Remarkably, these composites are fully recyclable with just the addition of water, maintaining tensile properties over tens of cycles. Life Cycle Analysis (LCA) shows that these recyclable composites demand significantly less energy, have a lower global warming potential, and reduced water usage compared to common construction products. Cold sintering offers a transformative way to convert waste into fully recyclable composites with tunable properties.