Development and characterization of sustainable cellulose nanofiber (CNF)-reinforced bio-adhesive films for wood-to-wood bonding

This study aimed to develop and characterize water-activatable bio-adhesive films designed for wood-to-wood bonding. The bio-adhesive films were prepared by blending polyvinyl alcohol (PVA) with chitosan (CS) and reinforced with varying amounts of cellulose nanofiber (CNF) using the casting method. The effect of CNF reinforcement on the films' physical (thickness, water solubility, and contact angle), morphological, thermal (melting and glass transmission temperature), mechanical (tensile strength), and adhesive properties (adhesive strength via single lap-shear) was evaluated.CS/PVA bio-adhesive films demonstrated an adhesive strength of 4 MPa. CNF reinforcement enhanced adhesive strength up to a CNF content of 5%; however, further increases in CNF concentration decreased the adhesive strength. CS/PVA films reinforced with 3% CNF exhibited the optimum adhesive strength of 4.20 MPa. Furthermore, the reactivated films retained their adhesive properties after repeated testing, maintaining an adhesive strength of 1.18 MPa. For comparison, polyvinyl acetate (PVAc)-based adhesive demonstrated an adhesive strength of 4.42 MPa.The bio-adhesive films demonstrated adhesive strength comparable to commercial PVA-based adhesives, while also providing additional benefits such as low waste production, uniformity, customizable sizing, and reusability. The reinforcement of CNF significantly enhanced the performance properties of the bio-adhesive films, making them highly suitable for sustainable wood-to-wood bonding applications.