Investigation of a new resin as an exterior adhesive to bond high moisture content veneers Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9g54xk84j

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  • A new carbohydrate-phenol based resorcinol resin (CPR resin) was synthesized by end capping a known carbohydrate-phenol based resole with resorcinol under basic reaction conditions. Synthetic parameters, such as duration of cook, pH, and the amount of resorcinol and formaldehyde were varied to produce resins with molecular weights (Mw) ranging from 1500 to 8000. These resins were tested for suitability as fast curing thermosetting adhesives to bond high moisture content veneers and as a cold-setting adhesive for producing glu-lam. The resin formulation which produced the best wood failure results was made with a glucose: urea: phenol: formaldehyde: resorcinol mole ratio of 1:0.75:1:2.0:1.3. When this resin (Mw 4776) was combined with liquid formaldehyde, paraformaldehyde, and walnut shell flour it exhibited a viscosity of 12,000 centipoise and a gel time of 35 minutes at room temperature. This adhesive was able to bond 18% moisture content veneers into 10" by 10" 3-ply plywood panels and lumber laminates into glu-lam panels. Plywood panels were produced with a glue spread ranging from 45 to 70 #/MDGL with pressing conditions of 175 psi and 285°F for 8 minutes. Microscopic observations of plywood gluelines showed severe wood fiber compression in the high moisture content veneers. Shear tests of specimens gave an average wood failure value of 85% after vacuum-pressure conditioning in water and a 75% average after boiling. The low value for the boil test seems to be related to the high moisture content of the veneers because cured adhesive samples were found to be insoluble in water. Wood failure values greater than 90% were obtained from shear specimens of the glu-lam panels for three conditioning methods (dry, vacuum-pressure, and boil). Carbon-13 NMR spectra of the CPR resins synthesized in this study showed that the glucosyl moiety is still intact in the polymer, perhaps as a glucosylurea derivative. This result is in contrast to some previous work which suggested furan polymers would be formed under the conditions used here. These CPR resins show excellent potential for use in gluing high moisture content veneers and in glu-lam applications.
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