Phenol-enriched hydroxy depolymerized lignin by microwave alkali catalysis to prepare high-adhesive biomass composites

Lignin, a by-product produced during pulping and papermaking, is a phenol-rich compound with excellent prospect to be used as a substitute for phenol in phenolic resin adhesive. Phenol-enriched hydroxy depolymerized lignin by microwave alkali catalysis is an effective method to prepare high-adhesive biomass composite. This study investigated the microwave digestion of lignin under different conditions of the alkali catalysis (sodium hydroxide) concentration, power, reaction time, and reaction temperature. The results show that on the condition of sodium hydroxide concentration of 0.3 mol/L, temperature of 170 degrees C, and time of 20 min, the highest phenolic hydroxy content obtained by depolymerization of lignin is 21.68%. SEM shows that the depolymerized lignin has no original basic constituent units and lignin-based phenolic resin has dense uniform pine needle units. Therefore, it has a high bonding strength of 1.934 MPa. The bonding strength and phenol content obtained by the microwave depolymerization method are much higher than those of other modification methods.

Automated summary

This study successfully prepared high-adhesive lignin-phenolic resin using microwave depolymerization method, showing great potential for applications. Under specific conditions of sodium hydroxide concentration, temperature, and time, the depolymerization of lignin yielded the highest phenolic hydroxy content, leading to the formation of dense and uniform pine needle units in the lignin-based phenolic resin with significantly higher bonding strength compared to other modification methods.