A Synergistic Strategy for Cost‐Effectively Reducing Formaldehyde Emission of Urea‐Formaldehyde Resin via Glyoxal Copolymerization and Urea Post‐Addition

ABSTRACT Although urea‐formaldehyde (UF) resin is extensively used in the wood industry for its cost‐effectiveness, good bonding performance, and technological applicability, reducing formaldehyde emission to levels comparable with non‐formaldehyde adhesives while maintaining cost efficiency remains a challenge. In this study, a novel glyoxal‐urea‐formaldehyde (GUF) resin adhesive with low formaldehyde emission (F **** grade), desired pre‐pressing performance, and good bonding properties was developed through the synergistic effect of the glyoxal copolymerization and the post‐adding urea as formaldehyde scavenger (FS). FTIR, NMR, XPS, DSC, and TGA analyses showed that the copolymerization formed substituted hydroxymethyl structures. The cross‐linking reaction between GUF resin and post‐added urea was enhanced, which reduced formaldehyde emission from GUF‐bonded plywood to 0.20 mg/L. This value is 33% lower than the 0.3 mg/L required for F **** grade plywood, according to JAS standards. The GUF‐bonded plywood maintained a warm water‐soaked wet strength of 0.74 MPa and a pre‐pressing strength of 0.82 MPa. The optimal conditions were 10% of glyoxal for copolymerization and 4.5 wt% of post‐added urea, which did not cause the cost increase of GUF resin. This synergistic strategy offers a cost‐effective approach to reduce formaldehyde emission from UF resin, demonstrating promising potential for broad application in the production of wood composites.