Bark Residues: A Model Study for Quantitative Determination

Paper published as Bulletin 35 in the UM Bulletin Forestry Series. This paper is a reprint from the Proceedings of the 22nd Northwest Wood Products Circle.https://scholarworks.umt.edu/umforestrybulletin/1019/thumbnail.jp

Microscopy of Abrasive-Planed and Knife-Planed Surfaces in Wood-Adhesive Bonds

Fluorescence microscopy (FM) disclosed no differences in wood cell structure between abrasive-and knife-planed Douglas-fir joints under constant conditions. However, after a one-cycle soak-dry exposure, formation of checks along the rays were visible in both abrasive- and knife-planed samples by fluorescence microscopy. For this same exposure, scanning electron microscopy revealed many radial cracks in the S2 layer and ruptures between the S1 and S2 layers in abrasive-planed samples. Knife-planed samples had few ruptures between the S1 and S2 layers and very few cracks in the S2 layer.Previous work showed that, although knife planing gave much smoother surfaces at the cellular level than did abrasive planing, both surfaces resulted in high strength bonds. When those bonded samples were subjected to a soak-dry treatment, however, strength of abrasive-planed samples was much lower than that of knife-planed samples.The substantially intact S2 layers in knife-planed samples, as revealed here, apparently retain considerable strength, while rupturing and cracking in the abrasive-planed samples explain the loss of bond quality reported in earlier work

Improving the fatigue resistance of adhesive joints in laminated wood structures

The premature fatigue failure of a laminated wood/epoxy test beam containing a cross section finger joint was the subject of a multi-disciplinary investigation. The primary objectives were to identify the failure mechanisms which occurred during the finger joint test and to provide avenues for general improvements in the design and fabrication of adhesive joints in laminated wood structures

Surface and Subsurface Characteristics Related to Abrasive-Planing Conditions

The goal of this study was to examine the quality of abrasively planed wood surfaces when variable grit sizes, feed speeds, and depths of cut are used. Our observations show that grit size and wood structure and density seem to have larger effects on the depth and type of damage than feed speed and depth of cut. Coarser grit sizes seem to cause greater damage than finer grit sizes.Surface damage in Douglas-fir occurs at every grit size, feed rate, and depth of cut combination; the earlywood shows more severe damage than the latewood. Surface damage is more variable in hard maple and yellow-poplar than in Douglas-fir. This variability may be due to different cell types present at the surface and the angle of intersection between the surface and the rays. Similar machining conditions do not always have similar effects on the surface quality even in the same wood species. Other factors, such as moisture content, between and within species density variations or belt conditions, might also contribute to the surface quality variability, but these were not explored

Tapered Double Cantilever Beam Fracture Tests of Phenolic-Wood Adhesive Joints: Part II. Effects of Surface Roughness, the Nature of Surface Roughness, and Surface Aging on Joint Fracture Energy

Tapered double cantilever beam specimens were used to test the effect of surface roughness, the nature of surface roughness, and surface aging on the fracture energy of phenolic-wood adhesive joints. The fracture energy and the failure characteristics of the joints were found to depend not only on the surface roughness but also on the method of surface preparation. The fracture energy increased monotonically with surface roughness for specimens derived from hand-sanded surfaces but exhibited a minimum for specimens obtained from machine-sanded surfaces. Generally, joints from hand-sanded surfaces had higher fracture energies than those derived from the machine-sanded surfaces. Within the joints derived from the machine-sanded surfaces, those sanded perpendicular to the direction of crack growth had higher fracture energies than those sanded parallel to the direction of crack growth. Aging surfaces prior to bonding significantly decreased adhesive joint strength.Notwithstanding the differences in roughness, microscopic examination revealed little difference in the appearance of the sanded surfaces. Adhesive did not penetrate hand-sanded surfaces to any appreciable extent, but did deeply penetrate both the vessel and fiber lumens on the machine-sanded surfaces. Microscopic examination of the fractured surfaces did reveal significant differences that related to the fracture toughness of the bond

Hydroxymethylated Resorcinol Coupling Agent for Enhanced Durability of Bisphenol-A Epoxy Bonds to Sitka Spruce

Epoxy adhesives can develop bonds to wood that are as strong as the wood itself, but only if the bonds remain dry. Once exposed to repeated water soaking and severe stresses from drying, epoxy bonds delaminate and fail to meet requirements for structural wood adhesives intended for exterior exposure. A new hydroxymethylated resorcinol (HMR) coupling agent, applied to lumber surfaces before bonding, chemically couples both epoxy adhesive and lignocellulosics of wood to produce bonds to Sitka spruce that are extraordinarily resistant to delamination. In this report, we explain and demonstrate the nature of this coupling agent and the mechanism by which it enhances the durability of bonds of a bisphenol-A epoxy adhesive to wood. When diluted with benzyl alcohol, an epoxy adhesive developed structural bonds in HMR-primed lumber laminates that met the 5% maximum delamination requirement of ASTM Specification D 2559. The USDA Forest Service has applied for a patent for this invention