Evaluating the effects of Kraft and Hydroxymethylated lignin on particleboard performance and environmental impact

In this study we investigate the effects of two industrial lignins, Kraft (KL) and hydroxymethylated lignin (HL), on the physicochemical properties of urea-formaldehyde (UF) adhesives and the performance of bonded particleboards. KL and HL were used to partially replace up to 15 wt% of UF adhesives, increasing viscosity beyond industrial requirements but enhancing internal bond strength. The curing peak temperature decreased from 84.3 °C (UF) to 83.3 °C (UF–5 % HL), while the heat of curing rose from 86.8 J/g to 107.5 J/g, confirming enhanced reactivity over KL. Mechanical performance improved notably, with the best results obtained for panels containing 10 wt% KL and 5 wt% HL, showing MOE, MOR, and IB increases of 38.4 %, 12.3 %, and 30.3 %, respectively, relative to control panels. Formaldehyde emissions were significantly reduced from 0.174 ppm for neat UF to 0.094 ppm for UF–15 % KL, approaching the Canadian regulatory limit. Despite viscosity challenges associated with both lignins, these findings highlight its potential as a bio-based UF adhesive modifier, offering enhanced performance and reduced formaldehyde emissions. Further optimization is required to lower HL's molecular weight and ensure industrial feasibility. This research provides a pathway for lignin valorization in sustainable wood composites, advancing eco-friendly alternatives for the forest products industry.