Volume 57, Issue 3

This is the first report of post-harvest wood staining in blackwood ( Acacia melanoxylon R. Br). In Tasmanian sawmills, an orange-brown stain commonly occurs upon cutting fresh blackwood. An investigation of the causal mechanism of stain development was completed using fresh flitches and stockpiled logs. Some fungi and bacteria were isolated from stained and unstained blackwood, but no species was consistently present in stained wood alone. Wood pH did not vary between stained and unstained wood, but there was some evidence of alterations in phenol composition. Blackwood extracts were analysed by HPLC and a minor phenolic compound was detected that was consistently found in stained samples and rarely in unstained. UV spectra indicated that this compound may be a quinone, but mass spectrometry data was inconclusive. Experiments with blackwood extracts showed that addition of oxygen (by means of H 2 O 2 treatment) increased absorbance in the “brown” wavelengths characteristic of stain. This supports the assumption that the stain is an oxidative chemical stain, as it develops quite rapidly from cut surfaces.

Albino strains of Ophiostoma floccosum , O. piceae and O. pluriannulatum were selected and screened for biological control of sapstaining fungi on New Zealand radiata pine ( Pinus radiata ). Albino strains were obtained through matings and single ascospore isolations from cultures of prevalent species in New Zealand. These strains do not synthesize the melanin-like hyphal pigments of common sapstaining fungi. Additional mating studies were also carried out to obtain isolates of O. piceae and O. floccosum that lacked pigmented fruiting structures. Several albino isolates of O. piceae with colorless synnemata and isolates of O. floccosum with little to no synnemata were obtained. Biological control potential of the albino isolates was evaluated in the laboratory by challenging them on wood chips with fungi that cause extensive sapstain in pine, Leptographium procerum , Ophiostoma piliferum and Sphaeropsis sapinea . Many albino isolates of O. floccosum , O. piceae and O. pluriannulatum were effective in stopping the challenge fungi from staining wood chips and were fast growing and colorless when grown unchallenged on wood chips. Selected albino isolates of O. pluriannulatum were used in two field trials in New Zealand to control sapstain. Several strains were found to significantly reduce dark sapstain as compared to the untreated control logs.

We propose a method to estimate fibre length distribution in conifers based on wood samples from increment cores processed by automatic optical fibre-analysers. Automatic fibre-analysers are unable to distinguish: a) fibres from other tissues, “fines”, and b) cut from uncut fibres. However, our proposed method can handle these problems if the type of distributions that fibre lengths and fines follow is known. In our study the length distributions of fines and fibres were assumed to follow truncated normal distributions, characterised by means and standard deviations of the two distributions. Parameter estimates were obtained by the maximum likelihood method. Wood samples from two 22-year-old Scots pine trees at breast height were used to evaluate the performance of the method. From stem discs at 1.5 m, adjacent samples of 5 mm increment cores and wood pieces were taken. The cores were trimmed 1 mm at each side and samples were, after maceration, analysed in a Kajaani FiberLab 3.0. The results showed that the method works well and gives a possibility to distinguish fine and fibre length distribution.

Bauer-McNett fractions of an aspen chemi-thermomechanical pulp showed a significant variation with respect to lignin content and sugar composition, and two of the fractions were found to be particularly rich in middle lamella and secondary wall material, respectively. The secondary wall lignin of aspen was found to contain larger amounts of non-condensed β-O-4 aryl ether structures than the middle lamella lignin and the difference was attributed to a larger amount of syringyl structures as revealed by thioacidolysis. Size exclusion chromatography of the thioacidolysis products from birch and spruce wood showed a larger part of lignin oligomers being present in the degraded spruce lignin. Moreover, birch lignin had a lower phenolic content than both aspen and spruce lignin. Thioacidolysis followed by Raney-nickel desulphuration was used for the analysis of hardwood lignin trimers.

The conformational preferences of the threo and erythro diastereomeric forms of a guaiacyl β-O-4 dimer have been investigated by molecular modeling using the CHARMM force field. Many low energy conformations have been identified for each diastereomer, showing that β-O-4 dimers can adopt a large variety of shapes. A consistent structural model has emerged that indicates different conformational behavior for the threo and erythro forms, corresponding to a preferential extended overall shape for the threo form. All the low energy conformers are stabilized by intramolecular H-bonds. In particular, the highly directional H-bond between the α or γ hydroxyl hydrogen and the aromatic methoxy oxygen governs the B aromatic ring orientation. However, it has appeared that the conformational preferences are predominantly governed by local steric interactions rather than by differences in the H-bonding pattern. From the satisfactory agreement between computed data (geometries and the Boltzmann distribution of the low energy conformers) and the experimental data reported in the literature (X-ray crystal structures and 3 J HαHβ NMR coupling constant), the CHARMM force field has been validated for the study of β-O-4 structures. Clearly, the molecular modeling calculations have led to an improved rationalization of the conformational data collected by experimental techniques.

Quantitative 31 P NMR analysis of residual lignin structures isolated from pulps pretreated by green liquor (GL) as a function of various operating parameters are discussed. Uncondensed phenolics and condensed hydroxyl groups decreased as the GL charge increased, but increased with increasing pretreatment temperature. During the cooking of pulps employing variable sulfidities and the addition of anthraquinone (AQ) or polysulfide (PS), various hydroxyl groups exhibited no obvious differences in the case of AQ addition, but dramatic changes were observed at variable sulfidities when the PS was used. The results implied that PS can exert a stronger catalytic effect under a higher sulfidity and result in more cleavage of the lignin macrostructure. The results also demonstrated a correlation between the nature of residual lignin and the efficiency of oxygen delignification based on the finding that the residual lignin in GL modified pulp exhibited a higher reactivity toward oxygen delignification.

The present paper reports our investigation into the use of two peroxygen reagents, peroxymonosulfate (PMS) and dimethyldioxirane (DMD), in bleaching sequences with peroxide to bleach wheat straw mechanical pulp, their reactivity with ferulic acid model compounds, and the likely relation between the two aspects. It was observed that combinations of PMS or DMD with peroxide offered a synergy leading to substantially improved brightness development in bleaching of wheat straw pulp. At the same time, these oxidizing reagents, especially DMD, were shown to be highly reactive with ferulic acid derivatives and increased the removal of ferulic acid from wheat straw pulp in bleaching. The results would suggest that the presence of non-lignin, peroxide-resistant chromophoric components, such as ferulic acid derivatives, might be an important factor limiting the brightness development of wheat straw mechanical pulp by conventional peroxide bleaching.

The relationship between hygroscopicity and the microsurface of heated wood was examined using the fractal surface dimensionality. The hygroscopicity of heated wood decreased with the increase in heating temperature to 250°C, and then decreased again above 350°C after increasing up to 350°C. This change corresponded to chemical changes in the wood, especially a reduction in hydroxyl groups, up to 250°C, and to the temperature dependence of the fractal dimensionality calculated from nitrogen gas adsorption above 250°C. The fractal dimensionality increased gradually from 100 to 250°C, followed by a rapid increase above 250°C with a peak at 350°C, and leveled off above 400°C. From the results, it is concluded that hygroscopicity of heated wood changes at 250°C and that it is dependent upon the chemical properties of wood below 250°C and upon the surface complexity above 250°C.

Storage of wood chips is preferred to storage of round wood, however, chip deterioration causes considerable problems in chip piles. Factors contributing to deterioration have, therefore, been studied to manage chip storage. The requirements of biopulping processes have renewed interest in the microclimate in these piles. The aim of this study was to assess the suitability of a 3000 ton softwood chip pile for colonization by a biopulping fungus. This study evaluated conditions such as temperature, moisture and CO 2 that developed over a 3-week period in the chip pile. Zones that formed within the pile varied in temperature, CO 2 concentration and moisture content. The high temperatures that developed in some areas in the chip pile could make a large volume (29%) of the chip pile unsuitable for colonization by mesophilic white-rot fungi. The moisture content in 24% of the chip pile reached 55%, but is not expected to have a large impact on biopulping. The areas of high temperature and high moisture also overlapped. Special management practices would, therefore, be required to produce a suitable environment in the chip pile for uniform colonization by biopulping fungi. High levels of CO 2 (12.7%) accumulated for a short period in some areas, but biopulping could still be effective at these levels.

The aim of this work was to study the wettability and chemical composition of heat-treated wood. Heat treatment was performed at 240°C under inert atmosphere on four European wood species (pine, spruce, beech and poplar). Contact angle measurements before and after treatment indicated a significant increase in wood hydrophobicity. Advancing contact angles of a water drop were in all cases systematically higher for heat-treated than for untreated wood. Chemical modifications of wood after heat treatment were investigated using FTIR and 13 C NMR analysis. FTIR spectra indicated little structural change which could be attributed either to carbon-carbon double bond formation or to adsorbed water. NMR spectra also revealed little chemical change except for the degree of cellulose crystallinity which was considerably higher in heat-treated wood and could explain the higher contact angles.

The potential for growth strain measurements for detection of tension wood was assessed in trees from two plantations of 10- to 11-year-old Eucalyptus globulus . Tension wood had commonly developed at or near the stem periphery of straight, vertical and dominant trees. At a localized level growth strain was found to be a good indicator of tension wood. However, in some cases moderate to low growth strain was also detected in some trees where tension wood had been overgrown with small amounts of normal wood. On a whole tree basis the relationship was not as clear. In this case growth strain values determined from multiple measurements appear to be influenced primarily by tissue close to the site of measurements and not by wood at relatively remote locations. In some cases low growth strain values were found in trees with significant tension wood and in others high growth strain values where little tension wood had developed.

Data sets of wood thermal properties differing in their complexity are presented and discussed. A number of numerical experiments of the heat transfer in wood are performed, and the predicted temperatures are compared to the experimental data obtained for European beech and Scots pine wood. The analysis of similarity of the heat transfer model together with the different empirical data of wood thermal properties to the results of the experiments showed that the lowest accuracy of temperature prediction was obtained for the constant data. Application of advanced models of the thermal conductivity required a large amount of input data and sometimes gave relatively low accuracy in temperature prediction. Application of the thermal conductivity models developed by the authors with the use of the Inverse Heat Transfer Problem approach produced the best temperature prediction accuracy.

In situ tensile tests parallel to the grain were carried out in an Environmental Scanning Electron Microscope (ESEM) chamber on Norway spruce ( Picea abies [L.] Karst.) samples. The ESEM-mode combined with a cooling device allowed examination of the specimens at a moisture content of 12% with unsputtered surfaces. By recording load-displacement curves and observing crack propagation simultaneously, a detailed image of fracture progress and tissue interaction could be described. Since these experiments required a sufficient specimen size and geometry, focus was concentrated on the methodology.