Adhesion of phenol-formaldehyde resin to waterborne emulsion preservatives in aspen veneer

Four waterborne emulsion preservatives — chlorothalonil (CTN), copper naphthenate (CUN), copper octoate (CUO), and zinc naphthenate (ZNN) — and the waterborne salt preservative, ammoniacal copper arsenate (ACA), were tested for their compatibility with phenol-formaldehyde (PF) adhesive. Aspen veneers were treated with preservatives to retentions of 0.2, 0.4, and 0.6 pcf, then bonded with PF adhesive after 10-, 15-, and 20-minute closed assembly times. Effectiveness of adhesion was determined by measuring shear strength and wood failure of bonds while saturated with water. Preservative type, retention level, and length of assembly time significantly affected the durability of bonds. Generally, wood failure decreased as retention level increased. ACA and CUN interfered less with adhesion than did the other preservatives. At their respective optimum closed assembly times of 15 and 20 minutes, PF bonds to veneers containing ACA and CUN exceeded 80 percent wood failure at all three retention levels. Bonds to veneer treated with CTN, CUO, and ZNN were not of commercial quality because the PF adhesive overpenetrated the treated wood. Overpenetration problems might be overcome by controlling the interactions of adhesive composition and surface-active agents in the preservatives.

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