Performance of Exterior‐Grade Plywood Composites Bonded With Formaldehyde‐Free Bio‐Adhesives Derived From Polyvinyl Alcohol, Citric Acid, and Microwave‐Assisted Carboxymethylation of Lignocellulose

ABSTRACT The growing global demand for adhesives has driven the development of renewable bio‐based adhesives through biomass valorization. Due to their polysaccharide content, oil palm empty fruit bunches (EFBs) are promising biomass resources for bio‐based adhesive development. This study aimed to optimize material utilization in bio‐based adhesive formulation using response surface methodology and to evaluate the adhesive performance of the optimized formulation of plywood. EFBs were modified via carboxymethylation assisted by microwave heating to produce carboxymethylated EFB (CM‐EFB) with a degree of substitution of 0.71 and successfully modified based on functional group analysis results. Optimization results indicated that only citric acid (CA) significantly influenced adhesive performance, yielding an optimal formulation with a desirability value of 0.995, consisting of 10 g polyvinyl alcohol (PVOH), 25 g CA, and 2 g CM‐EFB. The developed adhesive was characterized based on solid content, gelation time, rheological properties, functional groups, thermal stability, and hydrolytic stability. Further evaluation of the optimal PVOH/CA/CM‐EFB–based adhesive formulation in plywood manufacturing demonstrated its potential as an alternative for exterior‐grade plywood, meeting bonding strength (> 0.70 MPa) and delamination resistance (< 33.3%) without formaldehyde emission. This study revealed that the resulting exterior‐grade plywood met SNI 8916.2:2023 and JAS No. 233:2003 standards.