Nanoindentation-guided surface evaluation of high-loading rice husk/PPRC wood–polymer biocomposites: Effects of alkali treatment and talc hybridization

Rice husk (RH) is one of the abundant lignocellulosic biowastes which can be used to reinforce recyclable thermoplastic matrices, but the contribution of rice husk to the surface performance is highly dependent on filler loading, pretreatment and inorganic co-filler dispersion. In this study, high loading RH or alkali treated RH (RHT) wood-polymer composite sheets (10 and 15 wt.%) with and without 2 wt.% talc are evaluated. FTIR was employed as a supplementary technique to verify the incorporation of RH and maleic-anhydride-assisted coupling, while FESEM and quasi-continuous stiffness nanoindentation provided the bulk of the structure-property analysis. Alkali treatment was found to open and fibrillate RH surfaces, while talc showed lamellar particles that could fill in local voids. Within the 2 3 factorial design space examined (10 or 15 wt.% rice husk, untreated or alkali-treated, with or without 2 wt.% talc), nanoindentation identified 10RHT as the best-performing formulation for contact stiffness (48.06 mN/µm), 15RHT/2%TLC for elastic modulus (1.78 GPa) and 10RH/2%TLC for indentation hardness (≈0.25 GPa). A first-order-plus-interaction model fitted to the eight formulations showed that talc content was the largest single contributor to indentation hardness and that the loading × treatment interaction exceeded either main effect. In addition, the use of treated systems with talc also reduced time-dependent creep deformation, which is a sign of increased resistance to localized contact loading for sustainable WPC applications.