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Abstract
Synthetic adhesives, including urea-formaldehyde (UF) and phenol-formaldehyde (PF), have generally replaced biobased adhesives over the past 70 years because of their durability, low cost, and ease of use. However, in the past few years, concern about formaldehyde emissions, cost, and interest in biobased materials have renewed interest in soy adhesives. The use of soy adhesives can be broken into four stages: soy flour selection, dispersing/denaturating conditions, cross-linking chemistry, and bonding conditions. Generally soy flour is used because of its low cost, but the adhesive properties of the soy depend upon flour type, as well as adhesive formulation and processing conditions. For the flour to be used as an adhesive, it must be dispersed in a solvent, usually water. In this paper, we emphasized protein properties, as they are critical for forming good durable bonds. The dispersed proteins are globular because proteins fold in water so that the outer surface contains mainly hydrophilic groups, whereas hydrophobic groups prefer to be on the inside. Globular structures are sensitive to conditions, such as pH, added denaturants, temperature, and salts. Typically, soy proteins provide good adhesion to wood and other materials; however, these adhesives have poor water resistance without chemical cross-linking. Denaturants not only open or swell the protein globules to increase adhesion to the wood surfaces but also expose more sites for cross-linking these proteins. Soy adhesives, like most adhesives, need to be tailored to the application. Thus, an adhesive for plywood is very different from that for particleboard, and a core adhesive is different from a face adhesive for wood composites.
Keywords
Formaldehyde,
particle board,
soy flour,
adhesives,
testing,
soybean glue,
adhesion,
composite materials,
glue,
plywood,
urea-formaldehyde resins,
laminated wood,
wooden flooring,
crosslinking,
soy proteins,
water repellents,
viscosity,
durability,
bonding,
composite wood,
gluing,
bond strength,
failure,
denaturation
Citation
Frihart, Charles R.; Birkeland, Michael J.; Allen, Anthony J.; Wescott, James M. 2010. Soy adhesives that can form durable bonds for plywood, laminated wood flooring, and particleboard. In: Proceedings of the international convention of Society of Wood Science and Technology and United Nations Economic Commission for Europe--Timber Committee. 2010 October 11-14; Geneva, Switzerland. Paper WS-20: 12 p.
