Abstract
The most challenging part of developing acceptable adhesives for wood bonding often is to create a bond that will withstand exposure to wet conditions or wet/dry cycles. Products that pass these tests have been developed empirically, but the aspects that make it difficult for adhesives to pass these tests and systematically ways to develop more durable adhesive bonds have not been researched. The first aspect is that the swelling strain of wood can impart sufficient force to contribute to the bond fracture if interfacial strain between the adhesive and wood is not dissipated through the interphase regions. The second aspect is that adhesives for wood bonding fall into two groups (in-situ polymerized and pre-polymerized) based upon their chemical-structure-property relationships and their abilities to interact with wood cell walls. The in-situ polymerized adhesives are typically rigid monomers/oligomers that form the polymer backbone and numerous crosslinks after application to wood. Some of these adhesives can enter into cell walls and stabilize the wood interphase region to decrease interfacial strain. Pre-polymerized adhesives usually have only a low degree of reaction after application as well as flexibility in the backbone. Because these polymeric adhesives are generally too large to stabilize wood cell walls, they need to dissipate interfacial strain between the wood and adhesive through the adhesive interphase region. If adhesives do not form interphases that distribute strain, they are more likely to fail as wood swells upon absorbing moisture.
Keywords
Plant cell walls,
crosslinking,
polymerization,
elasticity,
mechanical properties,
strains,
stresses,
wood moisture,
adhesion,
adhesives,
moisture content,
glue,
glues and gluing,
bond strength,
flexibility,
wood bonding,
bonding,
failure,
durability,
swelling,
durability
Citation
Frihart, Charles R.; Wescott, James M. 2008. Why do some wood-adhesive bonds respond poorly to accelerated moisture-resistant tests? In: Proceedings for the 9th Pacific Rim bio-based composites symposium. 2008 November 5-8. Roturua, New Zealand. 51-58.
