Carboxylated cellulose nanofibers reinforced polyvinyl alcohol adhesive films with oxidative interfaces for eco-efficient wood bonding

Sustainable bio-based adhesive films are appealing alternatives to liquid adhesives during application, storage and transportation, but wet bonding performance may impede their wide applications. Herein, solvent-free adhesive films were developed by the solution-casting method using polyvinyl alcohol (PVA) and carboxylated cellulose nanofibrils (C-CNFs). C-CNFs, produced by deep eutectic solvent pretreatment combined with ultrasonic nanofibrillation, imparted hybrid PVA/C-CNFs (PC) adhesive films with enhanced mechanical and wood bonding properties. The PVA film with a 5 wt% addition of C-CNFs (PC5) possessed higher tensile strength and Young’s modulus (46.7 ± 3.6 MPa and 467.3 ± 6.5 MPa) than those of pure PVA film. Moreover, various oxidants were investigated to convert natural wood surfaces (NWS) into oxidant-activated wood surfaces (AWS). Improved bonding performances were observed from three-layer plywood formed by applying water-activated PC5 films on three different AWS and hot pressing at 120 °C and 1 MPa for 4 min with the use of 8 wt% sodium periodate, potassium dichromate and nitric acid, respectively. The dry, cold water and hot water bonding strengths of those plywood specimens all exceeded the class II plywood standard (0.70 MPa) by at least 1.3 times. Significantly, the hot water bonding strength of plywood bonded with AWS was almost 2.5 times higher than that of plywood bonded with NWS. This work provides valuable insights into the preparation of high-performance plywood by a fully bio-based adhesive film. • Carboxylated cellulose nanofibrils were obtained by a green deep eutectic solvent. • Adhesive films were fabricated using PVA and carboxylated cellulose nanofibrils. • The prepared films exhibited excellent thermal, mechanical and bonding properties. • Bonding performance was enhanced synergistically by wood surface oxidation. • This work provides an eco-efficient way for high-performance plywood manufacturing.