Valorization of Cork and High-Density Polyethylene and Polypropylene Wastes in Cork–Plastic Composites: Their Morphology, Mechanical Performance, and Fire Properties

The recycling of waste materials is a way of limiting over-consumption and optimizing the value of resources. Within the framework of a circular economy, this can be applied to post-consumer plastic wastes, but also to biobased by-products. Hence, this work deals with the design of composite materials by combining recycled high-density polyethylene (HDPE) and polypropylene (PP) coming from bottle caps and virgin cork of insufficient quality for cork stoppers. Different fractions (0, 5, 10, 15, and 20 wt%) of virgin cork were incorporated into recycled polymers (HDPEr and PPr). These composites were prepared without a coupling agent or fire retardant. The morphology and mechanical properties of the different conditionings were studied and compared. The thermal decomposition and the fire behavior of the composites were also investigated. Microscopy revealed the poor adhesion between the cork particles and polymer matrices. However, this limited interaction affected only the tensile strength of the PPr composites, while that of the HDPEr composites remained almost constant. The addition of cork was shown to reduce the time to ignition, but also to promote charring and reduce the heat released during the composite’s combustion. The feasibility of composites based on cork and HDPEr/PPr waste opens the way for their reuse.