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The gluability of certain hardwoods from Burma Chunsi, Khalid Salum

Abstract

The gluing properties of pyinkado (Xylia dolabriformis Benth.), thitya (Shorea obtusa Wall.), ingyin (Pentacme siamensis Kurz.), padauk (Pterocarpus macrocarpus Kurz.), in (Dipterocarpus tuberculatus Roxb.), and kanyin (Dipterocarpus sp.) from Burma were investigated. Three room temperature curing glues, phenol-resorcinol-formaldehyde (exterior), urea-formaldehyde (interior), and casein were used. Specific gravity, shrinkage, pH and extractive content were determined for each wood species and their influence on the gluing properties discussed. Block shear specimens for phenol-resorcinol-formaldehyde were tested dry, cold soak, boil and vacuum-pressure treated. Percent delamination was measured. Wood glued with urea-formaldehyde was tested dry and after cold soaking, whereas that glued with casein was only tested dry. In and kanyin (specific gravity 0.67 and 0.59, respectively) showed wood failure values above 90 percent and good shear strength with all the three glues. Pyinkado (specific gravity 0.75) showed high shear strength with all the three glues. It developed 81 percent wood failure with phenol-resorcinol-formaldehyde, 86 percent with urea-formaldehyde but only 22 percent wood failure with casein. Padauk (specific gravity 0.77) developed high shear strength with casein (2,709 psi), but slightly lower shear strength values with phenol-resorcinol formaldehyde (2,693 psi) and urea-formaldehyde (2,448 psi). It had 78 percent wood failure with phenol-resorcinol-formaldehyde and 87 percent with urea-formaldehyde but only 67 percent wood failure with casein. Ingyin and thitya (specific gravity 0.81 and 0.80, respectively) showed low shear strength and low wood failure percent with all the three glues. In and kanyin showed low percentage of extractives soluble in ether (1.8 and 1.3 percent, respectively), ethanol (0.5 and 1.4 percent, respectively), hot water (0.5 and 0.4 percent, respectively), and acetone (2.5 and 2.2 percent, respectively). No direct relationship was observed between percentage extractives in the solvents used and shear strength or gluability. If the influence of specific gravity is excluded, a trend of increase in glue joint strength with increase in wood pH was observed. The pH of the wood was from 4.47 to 5.09. The vacuum-pressure treatment reduced the dry shear strength of all species more so for in (37 percent) and kanyin (34 percent). All species, except ingyin and thitya, still showed high wood failure. High delamination percent was observed for pyinkado (22 percent), thitya (68 percent), and ingyin (34 percent), and low delamination for in (8 percent), kanyin (8 percent), and padauk (11 percent) with phenol-resorcinol-formaldehyde. The boil test was observed to reduce glue joint strength most for all species. The reduction was 57 percent for ingyin, 53 percent for in, 50 percent for kanyin, 30 percent for pyinkado and thitya, and 19 percent for padauk. Wood failure percent was high for all species except thitya and ingyin. Padauk, in and kanyin meet the requirements for exterior structural lamination with phenol-resorcinol-formaldehyde. Ingyin, thitya and pyinkado failed to meet the requirements. Padauk, pyinkado, ingyin, in and kanyin meet the minimum requirements for interior structural lamination with urea-formaldehyde. Kanyin, in and padauk are considered suitable for interior structural lamination with casein. Further study is recommended for ingyin, thitya, and pyinkado for gluing with phenol-resorcinol-formaldehyde for exterior structural lamination; pyinkado, ingyin and thitya for gluing with casein; and thitya for gluing with urea-formaldehyde for interior structural lamination.

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