Effects of Ethanol-Supplemented Phenol-Resorcinol-Formaldehyde Resin on Formaldehyde and Acetaldehyde Emissions from Glued-Laminated Timbers*

Aldehyde emissions from glued-laminated timbers bonded with phenol-resorcinol-formaldehyde (PRF) resin adhesives, some of which included ethanol as a solvent, were investigated. Four commercial ethanol-free and three laboratory-made PRF resins with varying ethanol content were prepared and used to manufacture sugi (Cryptomeria japonica D. Don) gluedlaminated timbers. The aldehyde emissions from these timbers were measured by a Japanese Industrial Standard small chamber method over an extended period. Three test samples, each with a differently oriented sealed surface, were also prepared for discussion of the mechanism. No relationship was observed between formaldehyde emission and either ethanol content or the orientation of the exposed area. However, acetaldehyde emission was significantly influenced by both parameters. When a cross-sectional surface was exposed, acetaldehyde emission decreased rapidly; however, conversely, when a cross-sectional surface was sealed, acetaldehyde emission remained constant and even increased gradually over an extended period, which was attributed to excessive acetaldehyde. When ethanol was present in adhesives in excess of 5 percent of the resin weight, excessive acetaldehyde may have been produced by enzyme alcohol dehydrogenase as previously reported and may spread into the wood, whereupon the acetaldehyde may have been emitted mainly from the cross-sectional surface rather than the other sides.