Microscopy of Acid-Activated Bonding in Wood

Fluorescence and scanning electron microscopy were used to reveal the effect of nitric acid on activated bonding in wood. The physical properties of the treated wood were analyzed and the feasibility of the bonding technique was evaluated. Results showed that the technique was too severe as it greatly damaged the wood. On both sides of the bond line the cells were crushed beyond identity. Below this zone was a zone of darkened wood, 20 to 50 cells, that was undistorted or partially distorted. Fractured surfaces in samples with high shear strength showed conventional wood failure, while low shear strength samples exhibited amorphous masses of destroyed wood and partially distorted cells. Longitudinal views of fractured surfaces indicated that the acid diffuses readily through cell walls, cell lumina, and intercellular spaces. Lignin and lignin-containing gap fillers applied during acid treatment did not seem to change the action of the acid on the wood. Addition of filter paper and walnut shell flour gap fillers caused deeper penetration of the acid into the wood

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

Resin Distribution in Hardboard: Evaluated by Internal Bond Strength and Fluorescence Microscopy

Product performance, to a large extent, depends upon the uniformity of resin deposition on or through the hardboard product. Presently, destructive testing of the hardboard, by measuring its internal bond (IB) strength, is the only method that will provide information about adhesive bond performance.The objective of our research was to compare IB test results with resin distribution patterns observed by microscopy of wet- and dry-formed medium- and high-density hardboards formed under varying conditions of pre- and post-blending variables.Using fluorescence microscopical techniques, we found that differences in resin distribution can be clearly detected. We observed that decreasing the resin solids content, mechanically increasing the fiber rubbing action with the resin, and changing the rate of resin application were effective ways for improving resin distribution in hardboard furnish. Our microscopic technique also showed that uniform distribution of the resin throughout the hardboard produced boards with the highest IB strengths.This research provides guidelines for estimating levels of IB strength based on the use of a developed fluorescence microscopical technique