ABSTRACT

The current wood adhesive industry relies mostly on petrochemicals, and is dominated by formaldehyde-based adhesives. However, petrochemicals are obtained from non-renewable resources, and formaldehyde is a known carcinogen. Hence, there is a growing interest surrounding the utilization of renewable resources for the development of environmentally friendly adhesive systems for production of bonded wood products. Due to their inherent adhesive properties, proteins are gaining popularity in this sector. The purpose of this chapter is to review the potential application of protein for the prospective development of industrial wood adhesives. Herein, we summarize the historical perspectives concerning the development of proteinaceous wood adhesives, potential proteinaceous feedstock resources for large-scale production of protein, and recent developments in protein- based wood adhesive formulations.

The proteinaceous feedstocks for adhesive development can be sourced as single cell-based proteins, plant-based proteins, and animal-based proteins. Among these, the plant-based proteins, specifically soy protein, have been widely explored in recent years for development of proteinaceous wood 2adhesives. On the other hand, only a handful of reports are available on utilization of whey protein and other waste animal protein for development of protein-based adhesive formulations. Thus far, no such studies have been conducted on single cell-based proteins.

Current bio-based adhesive technologies utilize such methods as protein denaturation by chemical, enzymatic, or thermal treatment, chemical modification of end functional groups, chemical crosslinking of protein molecules, co-reacting or blending of protein with a prepolymer, or a combination of any of these methods. Formulations developed by chemical crosslinking of denatured protein fragments or by co-reacting protein, after denaturation, with a phenol-formaldehyde prepolymer, have resulted in protein-based adhesive systems performing comparable to urea-formaldehyde- and phenol-formaldehyde-based wood adhesives. Both types of formulations using soy protein isolate have been successfully used for commercial production of composite wood products.

The high cost of soy protein isolate limits the widespread application of these products and therefore, are largely unable to replace petrochemical- based resins. Realizing this limitation of soy protein as well as other edible proteins, there has been renewed interest in waste animal protein as a renewable protein feedstock for formulation of wood adhesive systems. Waste animal protein is an undervalued protein stream that has shown great potential in wood adhesive applications. As newer and better technologies are being developed for efficient valorization of by-product streams in diverse industries, production of bio-based wood adhesives from such undervalued protein streams is inevitable in the not too distant future.