Wood Adhesives Based on Natural Resources: A Critical Review Part II. Carbohydrate-Based Adhesives

This Part II of the series of critical reviews on Wood Adhesives Based on Natural Resources concentrates on the various carbohydrates and their decomposition products, which might be used as wood adhesives. This includes the use of native carbohydrates as such as adhesives, and also with chemical modification of carbohydrates by natural and synthetic components. Crosslinking in order to improve moisture and water resistance is achievable by natural and synthetic chemicals. Most promising options are realized by decomposition of various carbohydrates to small, well-defined monomers, which then can undergo various reactions, yielding again polymers in order to create a bondline. Suitable monomers are various furan moieties, such as 5-hydroxymethylfurfural. Activation of cellulose and hemicellulose at the wood or fibre surface by chemicals, such as citric acid, enables bonding effects without addition of an external adhesive. So far, however, carbohydrates are used only in very small amounts as industrially applied wood adhesives, despite tremendous R&D effort made and a huge number of scientific papers and reports published.