Collapse,volumetric shrinkage,specific gravity and extractives in Eucalyptus and other species

Summary The influence of extractive content on the shrinkage behaviour in eucalypts was shown by mathematical extraction after making certain assumptions with respect to available data. The slope of the volumetric shrinkage/specific gravity (S/) ratio changed from negative to positive after the theoretical removal of alcohol/benzene/water soluble or NaOH soluble extractives. Statistical analysis of available data suggested that collapse was positively related to the encrusting and extraneous materials and negatively related to the polysaccharide cell wall component. Conversely, normal volumetric shrinkage was positively related to the polysaccharides and negatively related to lignin and extractive content. Mechanisms by which extractive content might influence collapse development were discussed. R-values (change in external volume during shrinkage or swelling per change in weight of equivalent volume of water) appeared to be negatively correlated with extractive content in eucalypts and calculations for other species showed that R progressively increased with cold and hot water extraction. Further analysis suggested that the apparent change in lumen dimensions suggested by particular R-values was mitigated by the bulking effect of extractives in the cell wall. A possible role for R as an indicator of dimensional stability was postulated.