Exploring the Potential of Post-Consumer Agroindustrial Subproducts for Nanocellulose-Biobased Adhesives

The valorization of agro-industrial byproducts as sources of functional polysaccharides is a promising strategy for developing sustainable materials. In this study, cellulose was extracted and purified from rice husk and apple pomace through sequential alkaline and bleaching treatments. Then it was chemically modified via TEMPO-mediated oxidation to obtain cellulose nanofibers (TOCNFs) with cellulose yields ranging from 23.8 to 32.4% for rice husk and 9.3–13.8% for apple pomace. Owing to its higher recovery and structural regularity, rice husk was selected for surface modification with 3-aminopropyltriethoxysilane (APTES). The resulting TOCNFs exhibited an average width of 8 nm and a carboxyl content of 0.48 mmol g−1. Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and nitrogen determination (1.72 mg g−1) confirmed the presence of aminosilane functionalities. APTES-modified TOCNFs were incorporated as active components to develop hybrid poly(vinyl acetate) (PVA) adhesives synthesized via in situ heterogeneous water-based polymerization. The influence of TOCNF surface chemistry and sodium dodecyl sulfate (SDS) on latex particle size, rheological behavior, and adhesive performance was systematically investigated. Latex particle size increased from 193 nm (PVA-SDS) to 625 nm with TOCNF-APTES and decreased to 247 nm upon SDS addition. Rheological analysis revealed pronounced shear-thinning behavior associated with the formation of percolated nanofibrillar networks, with low-shear viscosity increasing up to 477 Pa·s for TOCNF–APTES and decreasing to 370 Pa·s with SDS. Lap-shear testing (ASTM D905) showed substantial improvements in adhesive strength, reaching up to 250 kPa compared to PVA-SDS. These results demonstrate that surface-modified CNFs act not only as mechanical reinforcements but also as interfacially active components governing polymerization behavior, rheology, and adhesive performance. This exploratory study provides a proof-of-concept for the development of sustainable wood adhesives from agro-industrial byproducts.