HOW OVERDRYING WOOD REDUCES ITS BONDING TO PHENOL-FORMALDEHYDE ADHESIVES : A CRITICAL REVIEW OF THE LITERATURE . PART I . PHYSICAL RESPONSES

This review critically evaluates literature on the ways in which excessive drying (overdrying) inactivates wood surfaces to bonding, primarily for phenolic adhesives. In Part I of a two-part review, three inactivation mechanisms involving physical responses to overdryingare considered: ( I ) exudation of extractives to the surface, which lowers the wettability or hides the surface; (2) reorientation of wood surface molecules, which reduces wettability or places for bonding; and (3) irreversible closure of large micropores in cell walls. I believe that extensive evidence from wood bonding and paper sizing research supports the mechanism of extractives-induced low wettability as the cause for inactivation of Douglas-fir and southern pines. Molecular reorientation and irreversible micropore closure arc proposed wood inactivation mechanisms that involve loss of wettability and bonding sites.

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