Examination of adhesive penetration in modified wood using fluorescence microscopy

Abstract

Adhesive bonding takes place when an adhesive undergoes the conversion from liquid to solid. The liquid properties are needed for the adhesive to fully wet the bonding substance, and the solid properties are needed for the strength required for the union of the final product. The mobility of an adhesive depends heavily on its own physical and chemical properties and those of the wood surface upon which it is being applied. To improve the interaction, wood is often resurfaced prior to bonding to provide a smooth surface with minimal extractives and other debris. Scientists question whether this step is necessary for wood modified by acetylation, which creates a more hydrophobic material. The amount of adhesive penetration into a wood substrate has a direct correlation to the bond quality. Insufficient penetration causes minimal surface contact for chemical bonding or “mechanical interlocking.” Over-penetration of adhesive will create “starved‘‘ or dry bond lines. Fluorescence microscopy is an excellent method of examining adhesive penetration into lumens. It is possible for most adhesives to fluoresce either in their natural form (primary or auto-fluorescence) or when treated with chemicals capable of fluorescing (secondary fluorescence), such as added dyes or pigments. Fluorescence microscopy in our study revealed that the degree of penetration was good for both acetylated and unacetylated wood despite the difference in bond durability. In addition. good lumen penetration did not correlate to poor strength previously observed, therefore leading to the conclusion that lumen penetration does not always relate with bond strength or percent wood failure.

Citation

Chandler, Jermal G.; Brandon, Rishawn L.; Frihart, Charles R. 2005. Examination of adhesive penetration in modified wood using fluorescence microscopy. ASCSpring 2005 Convention and Exposition : April 17-20, Columbus, OH. [Bethesda, Md. : Adhesive and Sealant Council, 2005]: 10 p.