The synthesis of maleated nanolignin–polyvinyl alcohol–hexamine resin as a cold-setting wood adhesive

This work reports the development of a cold-setting plywood adhesive based on polyvinyl alcohol (PVOH), maleated nanolignin, and hexamine. The influence of the maleated nanolignin content (10, 15, and 20 wt%) and cold-pressing time (3, 6, 12 and 24 h) on the properties of the resin and the plywood panels bonded with it was investigated. Some physicochemical, structural and thermal properties of the synthesized resins were determined. The water absorption and shear strength of the plywood panels bonded with the resins were also measured according to the relevant standard methods. FTIR analysis indicated that the amount of the –OH at 3420 cm⁻¹ band and the C=O groups at 1740 cm⁻¹ band increased in the resins with increasing proportion of maleic anhydride-treated nanolignin from 10 to 20 wt%. Based on the physicochemical results obtained, the modification of nanolignin by maleic anhydride accelerates the gelation time and increases the viscosity and solids content of the resin compared to when virgin nanolignin is used. DSC analysis shows that the addition of maleated nanolignin significantly decreases the curing temperature of the resin from 56 to 48 °C. Based on the analysis of the panel results, higher mechanical strength (shear strength, MOE and MOR) and dimensional stability were obtained by treating nanolignin with maleic anhydride. The addition of 20 wt% maleated nanolignin in the adhesive while using a cold-pressing time of 24 h produced plywood which satisfies standard requirements.