Preparation of Formaldehyde-Free Bio-Based Plywood Adhesive Using Polyvinyl Alcohol and DES-Extracted Lignin Composite

The purpose of this paper is to develop a preparation method for a formaldehyde-free, low CO2 emission, and sustainable plywood adhesive. Previous research approached VOC emissions in formaldehyde-based adhesives via additives or VOC absorbents but failed to completely eradicate VOC emission. Lignin, as an abundant biomass feedstock, is a strong candidate for formaldehyde-free sustainable adhesive research. In this paper, three choline chloride-based (ChCl) Deep Eutectic Solvents (DES) were prepared for lignin extraction. ChCl and lactic acid showed the highest lignin solubility at 41.3% weight percentage and was used to extract lignin. The extracted lignin quality was verified using nuclear magnetic resonance. Lignin-polyvinyl alcohol adhesive was then prepared and hot-pressed to produce plywood, which were then subjected to mechanical and rheological testing. The end result was a plywood product that met GB/T 17657-2013 Chinese national standards with adhesive strength of 0.7 MPa. We hope this paper can act as reference for future works concerning formaldehyde-free adhesives.