Lignin-based wood adhesives: A comparison between the influence of soda and Kraft lignin

Due to the various chemical properties of lignins, one has different effects on the resins prepared with them. The aim of this research was to compare the influence of Soda and Kraft lignins on the physical and mechanical properties of the particleboards bonded with lignin-urea-formaldehyde (LUF) and lignin-phenol-formaldehyde (LPF) resins. According to the FTIR spectra and DSC analysis of lignin, Soda lignin exhibited higher phenolic hydroxyl groups and lower glass transition temperature (Tg) value compared to Kraft lignin. Also DSC analysis results indicated that the resins based on Soda lignin need a lower temperature for curing than those based on Kraft lignin. Based on physicochemical test results, the resins containing Soda lignin exhibit a faster gel time and higher viscosity compared to those prepared with Kraft lignin in the both types of resins. Generally physical and mechanical properties results indicated that the panels made from LPF resin have higher mechanical strength and dimensional stability compared to those made from LUF resins at constant level of lignin. The particleboards bonded with Soda-based resin yielded lower water absorption and formaldehyde emission as well as higher flexural strength and internal bonding strength when compared to those bonded with the Kraft-based resin. The mechanical properties of the particleboards bonded with LPG resins could be significantly improved by increasing percentages of lignin while it was decreased for LUF resin.