Methylphenol-Formaldehyde Resin as An Adhesive for Wood

Plywood panels of 1/8-inch Douglas-fir veneer were bonded, half with phenol-formaldehyde and half with methylphenol-formaldehyde resin adhesive. The resin adhesives were prepared in the laboratory. Plywood sheer specimens from the panels were tested for strength and the results obtained were used to compare the adhesives. The effects of veneer specific gravity, modification of the adhesives with walnut shell flour, and time interval between bonding and testing on the strength of the plywood were also studied. Strength values indicated that the two resin adhesives were alike. A distinct possibility with the methylphenol-formaldehyde was that, the methyl side chain would create a steric hindrance effect and thus reduce the number of reactive points on the ring of this chemical by blocking these points. However, the data did not show this and it was concluded that the two resins had about the same number of cross links when the adhesive set. Shear specimens from plywood bonded with either adhesive in which all veneer was of high specific gravity showed greater strength values than those in which all veneer was of lower specific gravity. The increase in strength was linear. It was apparent that heavier veneer makes stronger plywood if the glue bonds are adequate. The statistical analysis indicated that only the quadratic component of walnut shell flour was significant suggesting a curvilinear regression. Plywood bonded with adhesives in which 10 to 20 percent walnut shell flour had been added was stronger than plywood bonded with adhesives having no walnut shell flour or containing 30 percent walnut shell flour. The linear component of the time interval which was the interval of time between bonding and testing the plywood was significant. Plywood shear strength increased in a straight-line manner with time-interval increases up to 16 days. It was assumed that strength values would continue to increase with time up to a point and would then level off.

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