Microscopy of Acid-Activated Bonding in Wood
Keywords:Microscopy, cell structure, fractured surfaces, fillers, maple, birch, Douglas-fir
AbstractFluorescence 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.
Johns, W. E., et al. 1978. The nonconventional bonding of white fir flakeboard using nitric acid. Holzforschung32:162.nKelley, S. S. 1981. M.S. thesis, Department of Forestry, University of Wisconsin, Madison, WI.nRammon, R. M. 1981. M.S. thesis, Department of Forestry, University of Wisconsin, Madison, WI.nRammon, R. M., R. A. Young, S. S. Kelley, and R. H. Gillespie. 1982. Bond formation by wood surface reactions. Part II. Analysis of the chemical mechanism of nitric acid activation. Submitted to J. Adhesion.nYoung, R. A., R. M. Rammon, S. S. Kelley, and R. H. Gillespie. 1982. Bond formation by wood surface reactions. Part I. Surface analysis by ESCA. Wood Sci.14(3):110-119.n
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