Recent advancement in bio-based adhesives derived from plant proteins for plywood application: A review

Plywood, a multipurpose engineered wood with a huge global market of approximately 106 million cubic meters is constructed by bonding thin alternating perpendicular orientated sheets of wood together. As a consequence of this demand, the quantity of adhesives needed to bond the wood sheets is also vast, with urea-formaldehyde, phenolic, and melamine-formaldehyde resins being the most commonly employed due to their good bonding performance. However, these types of adhesives have many disadvantages, from being non-sustainable to emitting carcinogenic and mutagenic formaldehyde during use. As such, natural plant protein adhesives can be used as a potential alternative to traditional, toxic and non-renewable aldehyde-based adhesives for bonding plywood, with the advantages of attaining good adhesive performance, being widely available and sustainable. In this review, background information on protein composition and its interaction with wood are initially discussed, followed by the methodology necessary to pre-treat the protein. Important factors for determining bonding strength and the most likely bonding mechanism are also introduced. Furthermore, the state-of-the-art regarding bio-adhesives derived from a large variety of different types of plant protein for plywood bonding application are discussed. Current challenges with respect to water resistance, waste protein sources, and preservation time are also reviewed, followed by future prospects and directions within this field. It's worth noting that the statistical data and literature reported within this review were obtained from governmental reports, scientific journals and public patents between the years of 2009 and 2022, with most citations being from the last 5 years.