How Overdrying Wood Reduces Its Bonding to Phenol-Formaldehyde Adhesives: A Critical Review of the Literature. Part II. Chemical Reactions

Alfred W. Christiansen

Abstract


Literature dealing with the effect of excessive drying (overdrying) on wood surface inactivation to bonding is reviewed in two parts and critically evaluated, primarily for phenolic adhesives. Part I of the review, published earlier, covers physical mechanisms that could contribute to surface inactivation. The principal physical mechanism is the migration to the surface of extractives that decrease wettability. Part II of the review considers mechanisms involving chemical reactions: reduction of wood surface strength, oxidation and pyrolysis of wood bonding sites, and chemical interference with resin cure or bonding. In those cases where extractives are not the primary cause of inactivation, oxidation or pyrolysis probably is the major cause of inactivation. Inactivation of oak and of some Southeast Asian hardwoods may be due to the acidity of extractives, but the importance of decreased wettability caused by extractives cannot be dismissed.

Keywords


Drying;inactivation;adhesive;bonding;review;extractives;mechanism;wettability;oxidation;acidity

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