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UBC Theses and Dissertations
Foliage and bark as modifiers for plywood urea-formaldehyde resins Rosales Urbano, Danilo Adolfo
This work follows successful research by staff members at Forintek Canada Corp. in modifying and extending phenol-formaldehyde (PF) plywood resins with powdered tree foliages and barks. In the present study, two urea-formaldehyde (UF) resins, one commercial and one laboratory synthesized, were modified at 15, 30 and 45% addition levels with finely ground white spruce [Picea glauca (Moench.) Voss] foliage or western hemlock [Tsuga heterophylla (Raf.) Sarg.] bark. Two five-ply Douglas-fir [Pseudotsuga mensiezii (Mirb.) Franco] test plywood panels (38 x 38 cm) were made at 32kg/l00 m² double glueline spread level, six and ten min pressing time at 149°C. The commercial and laboratory synthesized wheat flour extended UF resins were used as controls. Shear strengths and wood failure percentages were recorded for sets of test specimens after conditioning at 22°C and EMC of about 6% (Dry test), one vacuum pressure cycle, five vacuum pressure cycles and boiling cycle. Most formulations with the commercial UF resin containing foliage or bark yielded good bond quality (wood failure and shear strength) similar to the control when tested dry and after one vacuum pressure cycle. Following multi-cycle testing, one formulation containing foliage gave similar wood failure percentage to the control. Two formulations containing bark improved glue bond durability yielding 3 to 12% higher wood failure than the control. Results with the laboratory resin were not as good, showing bond quality lower than with the commercial UF formulation. No formulation survived boiling treatment implying that no modification among those used improved UF resin durability under conditions of high moisture and-temperature. Both UF resins were successfully extended by various foliage and bark additions. It was found that both materials can be used as partial substitutes for the conventional extender wheat flour up to the 40% level. This information may be of use to some developing countries that import wheat to flour-extended UF resins used to bond interior grade plywoods. Such countries could benefit by making use of local tree foliages or barks.
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