Preboiling and drying wood samples of Eucalyptus regnans has shown that while in the heartwood shrinkage before reconditioning increased as a linear function of the logarithm of boiling time (BL), in the sapwood it decreased. These changes were interpreted as reflecting changes in green permeability through extractive modification which, for the sapwood, were sufficient to overcome any weakening of the cell walls through heat effects; in the heartwood, however, cell wall degradation apparently overshadowed any collateral increase in permeability, thus causing an increase in collapse.
Shrinkage after reconditioning described a cubic function with respect to B e and showed an overall reduction which was greatest after 16 minutes boiling time. Correspondingly, recoverable collapse was greatly increased through preboiling; it was shown that per cent collapse recovery in the heartwood could be increased by more than one third that of controls by preboiling for 8 minutes. The possibilities for industry application are considered.
Moisture content after reconditioning (M r) was greatest after about two minutes preboiling, then declined to be less than the control after t 6 minutes. Change in shrinkage after reconditioning and collapse were shown to be significantly related to change in M r. It was suggested that while M r may reflect relative permeabilities after reconditioning, this may not apply to permeability in the green condition.
Additional parameters derived from the data, viz. the intersection point, unit shrinkage, the R-ratio, 'collapse-free' shrinkage, total collapse and residual collapse described mostly significant, cubic relationships with the logarithm of the boiling time. Generally, the major inflection point of regression curves occurred after 8 or 16 minutes boiling.