Liquid glucose-polyvinyl alcohol blend wood adhesive modified by citric acid and its effect on physical, thermal, mechanical and performance properties

In this study, the crosslinking agent citric acid (CA) is added to liquid glucose (LG)-polyvinyl alcohol (PVA) blend-based wood adhesives to improve their mechanical and thermal properties. The effect of crosslinking has been investigated using various analytical techniques, including viscosity, water contact angle, differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). Several variables were investigated for their effects on performance characteristics, including glass transition temperature, pencil hardness, and tensile strength. Increasing the amount of CA and the content of LG were among these factors. The crosslinked blend-based films increased in pencil hardness value and showed less hydrophilic behavior in the water contact angle test. It is expected that nucleophilic hydroxyl groups in LG and PVA will react with free carboxylic groups to form crosslinks. By analysing FTIR spectra, it has been demonstrated that CA and the LG-PVA mixture interact. After 24 h of bonding for two distinct ratios of PVA to LG (i.e., 25:5 and 20:10), the lap shear bond strength for the wood substrates bonded with the modified blend increased by 250% and 263% for 0.3 wt% CA, respectively. Blends with 0.5 and 0.7 weight% CA showed a predominately plasticizing tendency because CA that has not been reacted acts as an external plasticizer. The glass transition temperature (Tg) and increase in viscosity were indicators of the reaction’s consequences due to the acidic pH. The newly developed crosslinked LG-PVA blend-based wood adhesive showed better mechanical and water resistance properties when compared to conventional LG-PVA blend-based wood adhesives.