Valorization of carnauba stalk biomass as a reinforcement for HDPE composites: structure-property relationships and performance analysis

This study investigates the environmental, economic, and technical potential of incorporating carnauba stalk particles as a renewable reinforcement in high-density polyethylene (HDPE) composites. Carnauba (Copernicia prunifera), a palm native to northeastern Brazil, is widely exploited for wax extraction, while its stalks remain underutilized and largely discarded. In this study, stalk particles were incorporated into HDPE at 5, 10, and 15 wt.%, and the resulting composites were characterized through morphological, mechanical, thermal, and creep analyses. Thermal analysis showed an increase of up to 23 °C in the maximum degradation temperature, indicating improved thermal stability. However, tensile testing revealed that increasing particle content reduced plastic deformation, promoting a ductile-to-brittle transition. Scanning electron microscopy (SEM) and X-ray microtomography (microCT) confirmed the presence of voids and weak interfacial adhesion, which limited stress transfer. Creep behavior showed similar long-term deformation among the composites, although specimens with higher filler loadings exhibited slightly greater compliance. Among the evaluated formulations, the composite containing 5 wt.% stalk particles presented the most balanced performance, combining improved thermal stability with acceptable mechanical behavior. These findings highlight both the potential and the current limitations of using carnauba stalks as a lignocellulosic filler, suggesting that improvements in interfacial bonding through processing adjustments or coupling agents could further enhance performance. Overall, this study supports the valorization of agro-industrial residues and contributes to the development of eco-friendly HDPE composites for non-structural applications such as automotive interior components and sustainable packaging.