Reduction of formaldehyde emission from urea-formaldehyde resin by maleated nanolignin

In the present work, urea-formaldehyde (UF) resin was modified by maleic anhydride-modified nanolignin. For this purpose, nanolignin was prepared by an acidic method and then different ratios of virgin lignin, nanolignin and maleated nanolignin (10, 20 and 30 wt%) were added to the UF resin during its synthesis. The synthesized resins were then used in plywood panels manufacturing. The physicochemical and thermal properties of the prepared resins were determined. Formaldehyde emission, water absorption and shear strength of the plywood panels bonded with the modified resins were also measured according to the relevant standards methods. FTIR analysis indicated that the peak corresponding to O-H was decreased by the treatment of nanolignin with maleic anhydride. The intensity of the 2800 cm-1, 1200 cm-1 and 1700 cm-1 bands related to respectively C-O, C--C and COOH bonds also increased in maleic anhydride-treated nanolignin. Based on the physicochemical results obtained, the modification of nanolignin by maleic anhydride accelerates the gelation time and increases the viscosity of the lignin-urea-formaldehyde (LUF) resin compared to when virgin nanolignin was used. DSC analysis shows that the addition of maleated nanolignin significantly decreases the curing temperature of the LUF resin. Based on panel analysis results, lower formaldehyde emission and higher mechanical strength and dimensional stability were obtained by treating nanolignin with maleic anhydride.