Structure–Property Relationships in Urea–Formaldehyde Bonded Napier Grass Composites: Influence of Lignocellulosic Chemistry on Interfacial Interaction and Thermal Stability

Abstract

The valorization of lignocellulosic biomass into value-added materials requires a fundamental understanding of structure–property relationships and interfacial interactions within composite systems. In this study, Napier grass (Pennisetum purpureum) was investigated as a renewable biomass feedstock for the fabrication of urea–formaldehyde (UF) bonded composites. Particleboards were prepared at varying resin loadings (11%, 13%, and 15%), and their physical, mechanical, and thermal behavior was systematically evaluated. The results reveal that increasing UF content enhances modulus of rupture (MOR), internal bonding strength (IB), and thermal stability, while reducing water absorption and thickness swelling, indicating improved interfacial adhesion and reduced porosity. Fourier transform infrared spectroscopy (FTIR) analysis indicated enhanced resin coverage and interfacial interactions between the lignocellulosic particles and UF resin, which contributed to improved composite performance. However, excessive resin loading (15%) resulted in a reduction in modulus of elasticity (MOE) and impact strength relative to the 13% UF formulation, attributed to localized brittleness and overpenetration of resin into the fiber structure. The optimized formulation demonstrated comparable performance to wood-based particleboards, highlighting the influence of lignocellulosic composition on bonding efficiency and stress transfer. Overall, this work establishes a clear correlation between chemical composition, interfacial interactions, and macroscopic properties, demonstrating the potential of Napier grass as a sustainable feedstock for advanced biobased composite materials.