Examination of Wood Adhesive Bonds via MicroCT: The Influence of Pre-Gluing Surface Machining Treatments for Southern Pine, Spotted Gum, and Darwin Stringybark Timbers

The successful manufacturing of glulam from several important Australian commercial timbers is quite challenging due to difficulties in gluing. Improvements in adhesive bond performance of spotted gum, Darwin stringybark, and southern pine timber have been achieved using alternative pre-gluing surface machining methods, e.g., face milling and sanding-post planing, when compared to conventional planing methods. In order to improve the understanding of the effects that different surface machining methods have on adhesive bond performance, this study used micro X-ray computed tomography and microscopy to assess key adhesive bond criteria. There was a considerable loss in the amount of adhesive after the wet and dry test cycles for all species. There was also an extremely high frequency of voids in the glue lines for all species, which would negatively impact bond strength and durability. Face mill prepared timber boards resulted in thicker glue lines and greater resistance to adhesion loss, compared to boards prepared via planing. For the two hardwood species, face milling also resulted in greater adhesive penetration; however, for southern pine, there were no significant differences in adhesive penetration between the three surface machining treatments. Adhesive penetration was much deeper in southern pine compared to spotted gum and Darwin stringybark.