Effects of Alcell Lignin Methylolation and Lignin Adding Stage on Lignin-Based Phenolic Adhesives

Abstract

To investigate the effects of lignin methylolation and lignin adding stage on the resulted lignin-based phenolic adhesives, Alcell lignin activated with NaOH (AL) or methylolation (ML) was integrated into the phenolic adhesives system by replacing phenol at various adhesive synthesis stages or directly co-polymerizing with phenolic adhesives. Lignin integration into phenolic adhesives greatly increased the viscosity of the resultant adhesives, regardless of lignin methylolation or adding stage. ML introduction at the second stage of adhesive synthesis led to much bigger viscosity than ML or AL introduction into phenolic adhesives at any other stages. Lignin methylolation and lignin adding stage did not affect the thermal stability of lignin based phenolic adhesives, even though lignin-based adhesives were less thermally stable than NPF. Typical three-stage degradation characteristics were also observed on all the lignin-based phenolic adhesives. Three-ply plywoods can be successfully laminated with lignin based adhesives, and it was interesting that after 3 h of cooking in boiling water, the plywoods specimens bonded with lignin-based phenolic adhesives displayed higher bonding strength than the corresponding dry strength obtained after direct conditioning at 20 °C and 65% RH. Compared with NPF, lignin introduction significantly reduced the bonding strength of lignin based phenolic adhesives when applied for plywood lamination. However, no significant variation of bonding strength was detected among the lignin based phenolic adhesives, regardless of lignin methylolation or adding stages.

Properties of Bark Particleboard Bonded with Demethylated Lignin Adhesives Derived from <i>Leucaena leucocephala</i> Bark

“…Additionally, finer lignin particles may have difficulty penetrating the pores and voids between the larger wood particles, resulting in weak bonding and a decrease in internal bonding strength [108]. Furthermore, finer lignin particles can create more void spaces between particles, reducing the effective contact area for bonding and weakening adhesion [109]. Finally, fine lignin particles might not form strong bonds with the wood particles due to their smaller size and surface characteristics, leading to insufficient bond strength and a decrease in internal bonding strength [110].…”

Advances of Modified Lignin as Substitute to Develop Lignin‐Based Phenol‐Formaldehyde Resin Adhesives

“…[43] This modification can effectively increase the activity of lignin, as well as the number of corresponding active sites to a certain extent. [44] Lignin prepared by this method is a suitable substitute for phenol in ligninbased PF resin adhesives. Demethylation can be performed using various methods with different catalysts, such as SO 3 2À (Scheme 3a), [45] HBr (Scheme 3b), [46] and a combination of 1dodecanethiol, hydroiodic acid, and iodocyclohexane (Scheme 3c).…”

Lignin as a green and multifunctional alternative to phenol for resin synthesis

“…[174][175][176] Among various adhesives, PR is a common type of adhesive since it can improve the adhesive strength as well as the water and weather resistance of the product. 177,178 PR can be used as an adhesive for the production of wood composites such as plywood (Fig. 6d), oriented strandboard, waferboard, hardboard and particleboard.…”