Effect of sodium lignosulfonate on bonding strength and chemical structure of a lignosulfonate/chitosan-glutaraldehyde medium-density fiberboard adhesive

Sodium lignosulfonate/chitosan-glutaraldehyde adhesive (L/C-G) has potential in environment-friendly wood-based panel adhesive applications. However, the effect of sodium lignosulfonate on the bonding strength and chemical structure of L/C-G was not elucidated. Herein, the role of sodium lignosulfonate in L/C-G was studied in detail by characterizing the mechanical properties and water resistance of medium-density fiberboards (MDFs) prepared using L/C-G as adhesives. The functional groups, thermal stability, and crystalline structure of L/C-G with various mass ratios of sodium lignosulfonate to chitosan were also characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction, respectively. The results show that an appropriate amount of sodium lignosulfonate in L/C-G was beneficial for its bonding strength, and the MDFs with 1:2 mass ratio of sodium lignosulfonate to chitosan showed superior mechanical properties and comparable water resistance with a commercial panel. Besides the reaction between sodium lignosulfonate and chitosan, guaiacyl units, or lateral chain of sodium lignosulfonate might also react with glutaraldehyde and result in C–O–C groups, helpful for the bonding strength of L/C-G.