Whole Wheat Flour Hydrolysate Modified Urea-Formaldehyde Resin with Enhanced Wet State Bonding Performance

Abstract

Urea-formaldehyde (UF) resin is widely used in wood-based panels due to low cost and fast curing, but its high brittleness, low wet strength, and formaldehyde emissions restrict outdoor and high-humidity applications. Traditional biomass modifiers (starch, cellulose, or lignin) rely on hydrogen bonding or simple condensation with UF, offering limited improvement in wet‑state bonding strength and stress distribution. This study used industrial-grade whole wheat flour to prepare hydrolysate (WWFH) via acid-catalyzed hydrolysis and optimized the co-condensation with UF resin by response surface methodology. The optimized wheat flour–based UF (WFUF) showed wet shear strength of 1.30 MPa (54.8% higher than 0.84 MPa for neat UF) and dry shear strength of 1.66 MPa. Formaldehyde emission was 0.59 mg/L, meeting the E1 standard. Characterization indicated that WWFH reducing sugars, protein degradation products, and pentosans crosslinked into the cured network through hydroxymethylation, urea linkages, and ether bonds. WFUF exhibited lower crystallinity, higher crosslinking density, and better thermal stability than neat UF. This work supports value-added use of low-cost whole wheat flour and development of high-performance biomass-modified UF resins.