State of research and trends in development of wood adhesives

We aim to present an overview of the status of adhesives in the wood industry, especially in the area of wood-based panels. The review summarizes the current state of research of two kinds of adhesives, i.e., synthetic adhesives and natural adhesives. Synthetic adhesives, consisting of urea-formaldehyde resins (UF), phenol-formaldehyde resins (PF), polyvinyl acetate emulsion (PVAc) and isocyanates, are widely used. For UF, most investigations are concerned with the reduction of free formaldehyde; for PF, most studies focus on finding new chemicals to replace phenol. PVAc has poor properties, but these can be improved by a blending reactions and copolymerization with other chemicals. Isocyanate is an environmentally friendly synthetic adhesive, but also suffers from inadequate properties. Natural adhesives, such as protein/starch, lignin and tannins, have poor bonding effect that limits their level of use, but their main advantages are that they are environmentally friendly and a renewable resource. Studies of modification can improve the bonding performances and gradually cause natural adhesives to become applied in industrial production. Some proposals for future development and the importance of environmentally friendly adhesives are provided, which will be helpful in future theoretical and experimental research.