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Turkey oak ( Quercus cerris L.) is characterized by some technological and aesthetical factors limiting its market value from its great potential. In this study, the effect of direct and indirect steaming on reduction in equilibrium moisture content (EMC) and colour variations was evaluated using a hyperspectral radiometer. Steaming treatments were carried out at 80°C for 48 h, and 120°C for 18 and 24 h, showing a reduction in EMC in the order of 8.1, 28.5 and 13.5, respectively, as well as very significant lightness (L) and hue (h°) modifications in comparison with untreated specimens. The spectral signature analysis confirmed that hydrothermal treatments modify wood sensibility to the light source in the entire spectrum range. The study supports the validity of hydrothermal treatments for improving technological and aesthetical properties of Turkey oak. [ABSTRACT FROM AUTHOR]

Abstract  Heat treatment of Pinus pinaster and Eucalyptus globulus wood was carried out by hot air in an oven for 2–24 h at 170–200°C and by steam in an autoclave for 2–12 h at 190–210°C. The colour parameters L*, a* and b* were determined by the CIELAB method on radial, tangential and transverse sections of untreated and treated wood, and their variation with regard to the treatment (ΔL*, Δa* and Δb*) were calculated in percent. For untreated eucalypt wood, lightness (L*) varied between 54.1 and 63.8% with a* between 7.4 and 8.5, and b* between 15.7 and 19.9. For untreated pine wood, L* varied between 67.3 and 76.1%, a* between 6.9 and 7.6 and b* between 16.3 and 24.1. Oven heat-treated wood became darker (ΔL* about 50% for 4% mass loss), and this was more for eucalypt wood under the same treatment conditions. In general, the contribution of red (a*) and yellow (b*) colour decreased with heat treatment. The transverse section of the two species darkened less for both the treatments with small differences between radial and tangential sections. Lightness decrease was related to chemical changes; with good correlations with glucose (R 2 = 0.96), hemicelluloses (R 2 = 0.92) and lignin (R 2 = 0.86). As regards colour, the heat treatments showed an interesting potential to improve the wood quality for solid timber products from pine and eucalypt. [ABSTRACT FROM AUTHOR]

Difficulties associated with the drying of ash eucalypts including collapse and internal checking, are discussed briefly. Prefreezing is one method that has been used successfully as a pretreatment for the drying of both hardwoods and softwoods from temperate and tropical regions. Prefreezing has produced marked reductions in shrinkage, collapse and drying degrade of the heartwood in the following species: California redwood, black walnut, black cherry, tanoak, toon, bamboo, and eucalypts. Little or no collapse reduction has been observed in New Zealand red beech, Pacific madrone, white birch, sitka spruce, and white ash. Limited response has been observed for numerous other species notably red oak and white oak. Reduced drying time in response to prefreezing has been observed in jarrah, karri, black walnut, Asian oak, toon, and California redwood; in Pacific madrone and tanoak the drying time increased. Not all species which respond with a reduction in shrinkage show reduced drying rates. Prefreezing wood at -20°C appears to be the most practicable temperature, although some species respond better at lower temperatures. However, in all cases, it is critical to ensure that the wood freezes and remains frozen for a number of hours. Indications are that the effect is retained for days to weeks and that the length of time of freezing need not exceed 12-24 hours. A number of explanations have been put forward to explain the behaviour of prefrozen wood. It is suggested that the main mechanism responsible for reduced shrinkage is due to the migration of moisture from the cell wall onto frozen lumen water. The moisture loss from the cell wall produces a 'cold shrinkage'; water to ice transformation leads to an expansion of liquid water in the lumen, thus imparting a compressive stress to the cell wall, which together with the moisture loss, make the cell more rigid, and therefore likely to shrink less. There is some evidence that certain types of wood extractives migrate into the cell wall during freezing and may play a role in the reinforcement of the wall. Reduced shrinkage after prefreezing has also been attributed to a reduction of the plasticising effect of wood extractives in wood dried at higher temperatures and low humidities; this effect does not occur at low temperatures. [ABSTRACT FROM AUTHOR]

Trees belonging to the genus Eucalyptus are specifically prone to developing damage due to collapse soon after felling. Observations on 150 trees of five Eucalyptus species from two growth sites, indicate that collapse occurs in the wake of the receding liquid water supposedly moving from the heartwood fibres into the rays, and from there to the vessels of sapwood and to the pith (heart shakes), respectively from where it evaporates. Collapse was observed over the entire cross section of stems. Anatomical evidences suggest a collapse modifying process across the stem from the pith to the cambium. Generally, the stresses generated cause tangential flattening of fibres and open radial/longitudinal splits in the tissue. Fibres seem to collapse in radial strings and also in small lumps scattered over the xylem. Based on their effect, the level of collapse stresses must be greater than the cross-grain tension strength but smaller than the longitudinal compression strength of the wet wood. The results suggest that the prediction of collapse susceptibility of standing trees is possible. [ABSTRACT FROM AUTHOR]

Brief presteaming of green, increment-core segments of mountain ash ( E. regnans F. Muell) produced small but significant changes in a number of moisture-shrinkage parameters. Both total volumetric shrinkage and recoverable collapse were significantly greater in presteamed samples, the increase in collapse being largely attributable to an increase in moisture content after reconditioning (M). The change in shrinkage after reconditioning also was significantly related to changes in M. The change in M was interpreted as reflecting altered permeability in presteamed material and was shown to be negatively related to estimated residual collapse. Initial moisture content and per cent saturation showed a highly significant decrease after presteaming, while green volume showed a small but significant increase. Neither the estimated intersection point, unit shrinkage nor the R-ratio were significantly different after presteaming. However, the unit shrinkage-specific gravity relationship was changed by presteaming such that it more closely complied with Stamm's approximation. [ABSTRACT FROM AUTHOR]

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