UBC Theses and Dissertations
Some gluing characteristics of ocotea usambarensis (engl.) Mungúre, Waweru
The gluability of a Kenyan tropical hardwood, camphor wood (Ocotea usambarensis) was investigated. Four room-temperature curing resin adhesives, phenol-resorcinol formaldehyde (PRF), urea-formaldehyde (UF), polyvinyl-acetate (PVA) and casein were used. Machine-planed wood samples were extracted with either hot water, 10% solution of sodium hydroxide, alcohol-benzene, surface treated with 3% nitric acid, or left untreated (control) before gluing. Using a double glue spread of 410.6 g/m² (85 lb per 1000 ft²) and the manufacturers recommended assembly times of each of the 4 glues, wood blocks approximately 25.4 x 101.6 x 304 mm (1 x 4 x 12 in) were bonded together. Gluing and pressing were carried out at room temperature (21-24°C). A pressing pressure of 1,379 kPa (200 psi) was applied over a period of 24 h. After conditioning, the joint strength and wood failure of both the untreated and treated blocks were determined by the ASTM standard glue block shear test. The blocks bonded with PVA and casein were tested dry. Block shear specimens for PRF were tested dry, after cold soaking, and boiling in water. Blocks bonded with UF were tested dry and after cold soaking in water. Statistical analysis showed that strength of adhesion joints bonded with PVA adhesive was significantly improved by surface treating with weak nitric acid, prior to gluing. However, none of the four wood pre-treatments significantly improved gluability of camphor wood with PVA as far as wood failure is concerned. Surface treatment of camphor wood with sodium hydroxide solution, and extraction with alcohol-benzene, prior to gluing, enhanced its gluability with casein adhesive. Removal of the alcohol-benzene-soluble and sodium hydroxide-soluble extractives significantly increased dry bond strength of the blocks bonded with PRF adhesive. However, only the alcohol-benzene extraction increased wood failure. The cold soak treatment generally reduced the bond strength of blocks bonded with PRF adhesive. Wood failure percentage was increased by the cold soak treatment except in blocks made with sodium hydroxide-treated wood. The boil treatment was observed to reduce bond strength in all the treatments except in the control. Other than in the sodium hydroxide treatment,the amount of wood failure increased as a result of the boil treatment. Untreated camphor wood bonded well with UF adhesive. Bond strength was significantly reduced by cold soak treatment.
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