Preparation And Characterization Of Phenol Formaldehyde Adhesives Modified With Steam Explosion Lignin

phenol formaldehyde (PF) resin is generally synthesized using phenol andformaldehyde under catalysts. It is the earliest industrial polymer material. PF is oneof the widely used adhesives in the wood processing field. Its consumption is secondonly to urea formaldehyde resin. PF resin has special significance especially in theproduction of water resistance, weatherability wood products. It has excellentbonding strength, water resistance, heat resistance, wear resistance and chemicalstability, especially the best boiling water resistance. PF resin has deep color, certainbrittleness and is easy to crack. The free phenol and formaldehyde content of PFresin are high and the material sources are non-renewable.Due to rapid rising oil price and energy crisis, searching for other lower costmaterials is an urgent issue for researchers. For example, using lignin formodification of PF resin can not only reduce the cost, but also realize recycling andrelieve the environment pressure. Lignin has lower reactivity than phenol, so the keyproblem of the preparation of lignin phenol formaldehyde (LPF) resin is improvingthe reactivity of lignin.In this paper, steam explosion lignin (SEL) was first phenolation in alkalinemedium. On the basis of the phenol hydroxyl content of lignin, the reactionparameters were optimized by single factor variable method. The phenolationconditions were optimized as: the lignin replacement was40wt%, sodiumconcentration was8wt%, reaction temperature was90℃, reaction time was1.5h. Atthe same time, the structure of SEL and ligninphenol was analyzed by chemicalanalysis and FTIR spectra. The results showed that the phenolic hydroxyl content oflignin increases by130%, and methoxyl content decreases by68%after phenolation. So the reactivity of SEL increased after phenolation and is suitable for preparation ofLPF adhesive.In this paper, the formaldehyde was directly added to the lignin phenol solutionto prepare LPF adhesive by in-situ polymerization. On the basis of bonding strength,free formaldehyde and phenol content of LPF adhesive, different factors wereinvestigated by single factor variable method. The reaction conditions wereoptimized as: the lignin replacement was40wt%, reaction temperature was80℃,sodium concentration was4wt%, formaldehyde to lignin ratio was10wt%, reactiontime was1.5h. The performance of LPF adhesive prepared under such conditions asfollows: pH value was11.5, solid content was47.07%, the viscosity was335mPa. S,free phenol content was3.96%, free formaldehyde content was0.43%, the bondstrength was1.110MPa, the performance of adhesives and the plywoods all met theChinese National Standard (GB/T14732-2006). When the lignin replacement ofphenol reaches70wt%, the bonding strength of LPF adhesive also meet the ChineseNational Standard.In the preparation of LPF adhesive, the free formaldehyde and phenol contentcould be reduced by adding a certain amount of urea as formaldehyde capture agent.While the water resistance of urea formaldehyde resin is poorer than that of phenolformaldehyde resin, even a small amount of urea formaldehyde produced by ureaand formaldehyde also affects the water resistance of the adhesive. When the ligninreplacement was40wt%and the LPF adhesive was prepared on the optimumconditions, the addition of4wt%urea decreased the free formaldehyde and phenolcontent, the bonding strength of LPF adhesive also meet the Chinese National...