碱液化处理木质素基酚醛树脂的制备及性能研究

Preparation and Properties of Alkali Liquefied Lignin-Based Phenolic Resin

以蔗渣木质素为原料,经碱液化预处理后部分替代苯酚制备酚醛树脂胶黏剂,探讨碱液化前后木质素的结构变化及其对酚醛树脂胶黏剂理化特性的影响。结果表明:经碱液化处理后,木质素的数均分子量由11 270 g/mol降低至3 578 g/mol,分子量分布(PDI)由1.371提高至2.210,酚羟基和羰基含量分别提高29.83%和15.66%。木质素酚醛树脂胶黏剂的黏度和胶合强度随着原木质素含量的增加呈现先增加后减小的趋势,游离甲醛含量高于纯酚醛树脂。经碱液化预处理后,木质素对苯酚最佳替代率由30%提升至50%~60%。当对苯酚替代率为50%时,碱处理木质素基酚醛树脂具有最优的综合性能,产品的固含量、黏度、胶合强度和游离甲醛含量分别为42.20%、597 mPa·s、2.11 MPa和0.25%。

Phenolic resin adhesive was prepared from bagasse lignin by partially substituting phenol after alkali liquification pretreatment. The effects of alkali liquefaction pretreatment on the lignin structural and the physical and chemical properties of lignin-phenolic resin adhesives were discussed. The results show that after alkali liquification pretreatment the number average molecular weight of lignin is reduced from 11 270 g/mol to 3 578 g/mol, the polymer dispersity index(PDI) of lignin is increased from 1.371 to 2.210, the content of phenolic hydroxyl group and carboxylic group is increased by 29.83% and 15.66%, respectively. The viscosity and bonding strength of lignin phenolic resin adhesive increase first and then decrease with the increase of original lignin content, and the free formaldehyde content is higher than that of pure phenolic resin. After alkali liquefaction pretreatment, the substitution rate of lignin for phenol increases from 30% to 50%~60%. When the substitution rate of phenol is 50%, alkali treated lignin-based phenolic resin has the best comprehensive performance. At this time, the solid content, viscosity, bonding strength and free formaldehyde content of the product are 42.20%, 597 mPa·s, 2.11 MPa and 0.25%, respectively.