Gypsum-Based Composites with Recycled PP/HDPE Pellets for Circular Material Development: A Comprehensive Characterisation

Managing plastic waste is a great challenge for today's society, and it is increasingly necessary to find solutions to the large amount of plastic waste dumped annually in the oceans. The main objective of this research is to perform a comprehensive characterisation of different gypsum-based materials incorporating recycled PP/HDPE pellets from the recycling of discarded fishing nets in the Mediterranean Sea. For this purpose, composites were developed with a partial substitution of the original material by these pellets, up to 30% by volume, while maintaining a water/gypsum ratio of 0.65 by mass. The results showed that even in the most unfavourable case, with a 30% replacement in volume by these recycled pellets, flexural (2.72 MPa) and compressive (7.15 MPa) strengths higher than those required by the standards were obtained, with good integration of the residue in the matrix. Also, there was a decrease in total water absorption of up to 20.5% compared to traditional gypsum. The thermal behaviour study showed that a minimum conductivity value of 292.3 mW/m K was obtained, implying a decrease of 14.9% from the control series. In addition, a life cycle analysis was conducted, obtaining a reduction in environmental impact of up to 13.1% in terms of CO₂ equivalent emissions. Overall, the composites obtained represent a sustainable alternative to producing prefabricated plates and panels for building construction.