Lignocellulosic residues are increasingly explored as alternatives to wood in particleboard production, fostering sustainability within the circular economy. Beyond these, non-lignocellulosic wastes such as plastics are gaining attention for enhancing panel durability and performance. This study evaluates waste high-density polyethylene (HDPE) as a partial substitute for adhesive resin in sugarcane bagasse-based medium-density particleboards. The objective was to valorize agricultural and plastic residues while reducing reliance on petroleum-based resins and associated environmental impacts. Panels (750 kg/m³) were produced with two face layers of sugarcane bagasse and a core layer combining bagasse and HDPE, bonded with castor oil-based polyurethane resin at 8% and 12% contents. Physical and mechanical performance was assessed against national and international standards, complemented by natural and accelerated weathering tests. A comparative life cycle assessment (LCA) was conducted to benchmark hybrid panels against conventional particleboards. Results showed that incorporating HDPE allows for resin reduction without compromising performance, meeting standard requirements for several applications. The LCA indicated lower environmental burdens in 8 of 10 impact categories for hybrid panels relative to conventional ones, underscoring their potential to reduce fossil resource use and emissions. The findings demonstrate that integrating waste plastics into particleboard production not only improves resource efficiency but also delivers tangible environmental benefits. This approach offers a scalable pathway for advancing sustainable materials, closing waste loops, and supporting circular economy practices in the wood-based panel industry.

Large-scale and recurrent Sargassum beaching events along the coastlines of Brazil, Mexico, and the Caribbean pose significant environmental, social, and economic challenges due to biomass accumulation and decomposition. Meanwhile, valorization of underutilized waste streams into composite materials can advance circular economy strategies. Building upon previous findings on Sargassum-based particleboards, this study investigated increased pressing temperature and residual high-density polyethylene (HDPE) incorporation as strategies to improve dimensional stability. Medium-density particleboards were manufactured from Sargassum biomass and sugarcane bagasse, with and without residual HDPE, using bio-based castor oil polyurethane resin. The panels were characterized regarding physical, mechanical, and thermal properties to assess their suitability for non-structural applications. HDPE-containing formulations showed reduced 24 h thickness swelling from 21% to 15%, while exhibiting an overall reduction in mechanical performance, particularly in bending and internal bond strength properties. Despite this trade-off, the developed particleboards demonstrated potential for furniture and indoor building applications while simultaneously valorizing marine, agro-industrial, and plastic residues. These findings support Sargassum biomass as a sustainable feedstock for particleboard production and indicate that residual HDPE can improve 24 h thickness swelling performance, contributing to circular economy strategies and low-impact material development for applications across the built environment sector.