Relationship of some physical properties with extractive content in selected Philippine wood species

Twelve Philippine hardwood species were studied to determine the relationship of their specific gravity, fiber saturation point and volumetric shrinkage with percentage extractive content. This study was also conducted to determine the effects of extractives on the interrelationships among the physical properties of wood considered. Twenty four matching wood blocks were cut within the heartwood periphery of a disk from each tree of every species, for the determination of percentage extractive content, and the unextracted and extracted counterpart values for all properties studied. Analysis showed a generally wide and significant variation of all the properties studied. Radial variations of extractive content, specific gravity and volumetric shrinkage was found to be generally increasing towards the heartwood periphery while fiber saturation point follows the reverse trend. Extraction treatment consistently increased the fiber saturation point and volumetric shrinkage values while the specific gravity decreased logarithmically with increasing percentage extractive content. This is indicative of the less hygroscopicity and good dimensional stability of wood in service when containing extractives appreciably. Furthermore, results also revealed a negative and positive correlations of fiber saturation point and volumetric shrinkage, respectively, with specific gravity; while both fiber saturation point and volumetric shrinkage were positively correlated with each other. Combined effects of extractive content and specific gravity on the variations of fiber saturation point and volumetric shrinkage was found to be statistically significant. Isolating the interaction of specific gravity significantly increased the correlation of volumetric shrinkage with extractive content, while notably altered the logarithmic relationship of fiber saturation and extractive content to a quadratic pattern.