Bertholletia excelsa Shell–Based Wood–Plastic with Upcycled Polypropylene: An Amazonian Feedstock for Circular Bioeconomy Applications

Environmental accumulation issues arise from discarded waste, synthetic, and natural polymers in landfills, whose slow degradation exacerbates the problem. These materials can be upcycled as renewable feedstocks and properly reused. Therefore, this research examines the fabrication of an extruded wood–plastic suitable for large-scale production, made from recycled polypropylene (PP) and reinforced with plant-based fillers extracted from the lignocellulosic shell of Bertholletia excelsa, well-known as Castanha-do-Pará (CDP), offering a cost-effective and sustainable solution that minimizes waste and fosters a circular economy, enhancing its mechanical properties and environmental benefits. The fractions of 10%, 20%, and 30% by mass of CDP were tested. X-ray diffraction (XRD) analyses indicated that CDP acts as a nucleating agent for the polymer’s beta phase. Fourier-transform infrared spectroscopy (FTIR) indicated interactions between the components as the filler content increased. Scanning Electron Microscopy (SEM) images revealed increased void regions at different CDP contents, corroborating the impact results. These outcomes indicate that incorporating 20%–30% Castanha-do-Pará filler can enhance the wood–plastic flexural properties. This reduces reliance on purely synthetic materials and positions Bertholletia excelsa wood–plastic as a valuable, potentially large-scale product.