mold resistance test on adhesives used in wood composite products

There are increasing expectations for products to be resistant to mold growth even when subjected to moisture conditions for which they were not originally intended. Products may be subjected to wetting during shipment, storage, or from exposure to leaks while in use. Although the susceptibility to mold growth of many wood composite products in the marketplace has been investigated, the ability of the adhesives used in the manufacture of the products to support mold growth is unknown. APA-The Engineered Wood Association approached Forintek Canada Corp. (now FPInnovations-Forintek Div.) to investigate the potential for mold growth to occur on surfaces of samples of six selected adhesives commonly used to manufacture wood composite products. The American Wood-Preservers' Association (AWPA) E 24 Standard Method of Evaluating the Resistance of Wood Product Surfaces to Mold Growth was used to determine susceptibility of adhesive samples to mold growth. The test evaluates susceptibility to growth of a broad range of molds from both natural and artificial inocula for up to 8 weeks on sample surfaces. In addition, a repeat test was performed on two adhesives, phenol formaldehyde (PF), with filler and extender used in plywood (PF-ply) and phenol resorcinol formaldehyde (PRF), with filler, after the first test indicated incomplete curing of samples. Test results show that wood controls, southern pine sapwood and aspen sapwood were susceptible to mold growth. PF-ply and PRF were also susceptible to mold growth on both incompletely cured and cured samples, although little growth occurred during the first 2 weeks on PF-ply. Melamine urea formaldehyde (MUF) was not susceptible to mold growth for the first 4 weeks, and supported very little growth up to 8 weeks. PF-OSB (phenol formaldehyde used in oriented strand board), P-methyl-enediphenyldiisocyanate (PMDI), and urea formaldehyde (UF) were not susceptible to mold growth for the duration of the 8-week test. None of the adhesives was significantly more susceptible to mold growth than southern pine or aspen sapwood. Moisture contents (MC) of southern pine sapwood and aspen samples approximated the expected equilibrium MC of solid wood for the conditions in the chamber.