Volume 60, Issue 6

The topochemical distribution of phenolic deposits in the vessels of afzelia ( Afzelia spp.) and merbau ( Intsia spp.) heartwood was investigated by means of cellular UV microspectrophotometry (UMSP) to characterise the chemical composition and synthesis by pit membrane-associated enzymes. UV absorbance spectra of the deposits attached to the vessel walls of merbau are characterised by a distinct maximum at a wavelength of 368 nm representing the UV absorbance of pure robinetin (C 15 H 10 O 7 ). Deposits in the vessels of afzelia display a typical spectrum of kaempferol (C 15 H 10 O 2 ) with two distinct maxima at 270 and 350 nm. The pit membranes and pit canals of associated vessel and parenchyma cells are impregnated by these compounds. These results verify the assumption that the synthesis of deposits in afzelia and merbau is regulated by pit membrane-associated enzymes.

The topochemical distribution of accessory compounds responsible for wood colouration during heartwood formation and processing of black cherry ( Prunus serotina ) is restricted to the axial and ray parenchyma cells. (+)-Catechin, taxifolin, aromadendrin, eriodictyol, naringenin, 4′-methoxynaringenin and prunin were identified in acetone/water extracts. However, the colour of wood after extraction is still reddish-brown, indicating that the coloured material is polymeric (cross-linked, condensed). It was demonstrated that (+)-catechin plays a pivotal role in the development of heartwood colour. Its concentration at the sapwood/heartwood boundary decreases, presumably due to the formation of non-soluble polymeric proanthocyanidins. Heat treatment of heartwood during veneer production intensifies the reddish-brown heartwood colour, probably by promoting the polymerisation of (+)-catechin and other flavonoid monomers.

Cell wall modifications in vessels and fibres of wound wood of Populus tremula L.× P. tremuloides Michx. formed after mechanical wounding have been examined by light microscopy, transmission electron microscopy, and UV microspectrophotometry (in scanning and point measurement mode), mainly focusing on the lignin distribution. With this goal, wound xylem within lateral wound callusis was collected after response periods of up to 23 months. Vessels and fibres in wound xylem deviated from their usual axial orientation. Vessels within the wound xylem were smaller in diameter and shorter in length. Xylem fibres were also shorter and developed thicker walls, especially in tissue adjacent to the wound. Cell walls and cell corners of these fibres showed on average a higher lignin content and a modified lignin composition. These wall changes probably enhance disease resistance of the wound tissue. With increasing distance from the wound edge, the modifications diminished and finally disappeared.

Brown rotted Scots pine ( Pinus sylvestris ) sapwood was studied using scanning UV microspectrophotometry. Wood blocks were exposed to the fungus Coniophora puteana (Schum.: Fr.) Karst. (BAM Ebw.15) for 6, 8, 10, 30, and 50 days. No wood weight loss was detected in the initial decay periods. On the other hand, point analyses of lignin distribution in wood cells revealed higher absorbance after 6–10 days of decay, which we interpret as an increase in the absorption coefficient of lignin due to its oxidative modification by the fungus. Uneven wood degradation occurred in the later periods (30 and 50 days), with both significantly decayed and visually sound cells observed. The decayed cells showed a higher absorbance at 280 nm, although the apparently sound cells were also degraded to a lower extent. Degradation of lignin-rich compounds in middle lamellae and cell corners was not observed during fungal attack.

Gibberellins (GAs) are important regulators of shoot growth in trees. We studied the kinetics of xylem formation in hybrid poplar ( Populus tremula L.× P. tremuloides Michx.) in which the key regulatory gene gibberellin acid 20 oxidase (GA20-oxidase) isolated from Arabidopsis is overexpressed. Increments in the height and radius of shoots were registered by high-resolution laser measurements. The anatomical and chemical structure of mature xylem cells was studied by light electron microscopy and UV spectrophotometry. Transgenic plants showed an increase in height growth, but a lower speed of cell elongation during primary growth compared to wild-type plants. During the first year of growth, transgenic plants showed a higher radius increment, an increase in the period of cell expansion of vessels and fibres and their final size, and a higher lignin content of the compound middle lamella between fibres compared to wild-type plants. In contrast, during the third year of growth, only a slight increase in the period of cell expansion of fibre cells was observed in transgenic compared to wild-type plants. Analyses of GA20-oxidase expression in leaves and shoots of 6-month- and 3-year-old plants of three different independent transgenic lines revealed a decrease in its expression only in shoots but not in leaves of the 3-year-old plants. The results indicate that overexpression of the GA20-oxidase gene in young shoots of transgenic poplar predominately affects cell expansion, while no GA20-oxidase expression was observed in shoots of 3-year-old transgenic plants, resulting in wild-type xylem cell development.

The gelatinous layer (G-layer) formed on the lumen wall in early- and latewood fibres of poplar and birch tension wood was characterised using a novel molecular marker specific for crystalline cellulose in conjunction with fluorescence and FE-SEM microscopy. Crystalline cellulose was localised using a cloned Cel7A cellulose-binding module (CBM1 Hj Cel7A ) from the fungus Hypocrea jecorina conjugated directly to FITC/TRITC or indirectly via a secondary antibody conjugated to FITC for fluorescence microscopy or to gold/silver for FE-SEM. With the CBM1 Hj Cel7A conjugate, the G-layer was clearly distinguished from other secondary cell-wall layers as a bright green layer visible in fibres of tension wood in fluorescence microscopy. FEM-SEM images revealed the supramolecular architecture of the G-layer of poplar wood, which consists of well-defined, often concentrically orientated, cellulose aggregates of the order of 30–40 nm. The cellulose aggregates typically have a microfibril angle of almost 0°. Studies on cellulose marked with CBM1 Hj Cel7A followed by Au labelling and Ag enhancement complemented the fluorescence observations. The studies demonstrate the usefulness of this novel molecular marker for crystalline cellulose in situ , which was previously difficult to localise. Further proof of distinct cellulose aggregates was observed.

Corsican pine ( Pinus nigra ) sapwood was chemically modified with acetic or hexanoic anhydride to a variety of weight gains. The modified wood was exposed to the brown rot fungus Coniophora puteana , and the relationship between weight loss due to decay and weight percentage gain, or degree of hydroxyl substitution, was determined in a 16-week exposure test. The effect of exposure time and the strain of C. puteana upon the decay protection threshold of acetylated Corsican pine was also examined.

Birch and pine wood specimens were colonized by individual isolates of 12 brown-rot, 26 white-rot, six soft-rot and four blue (sap)-stain fungi. Homogenized wood was subsequently extracted in 75% ethyl acetate and centrifuged. The filtered extracts were analyzed for their iron-reducing capabilities using a ferrozine-based assay. Agar fungal cultures were also examined directly using a spot test for iron reduction. Extracts from wood colonized by brown-rot fungi showed significantly greater iron-reducing capability than extracts from wood colonized by white-rot or non-decay fungi. Results of the spot test ratings were highly variable, but in general the greatest color responses were associated with the brown-rot cultures. The ability of brown-rot fungi to produce compounds and/or modify the wood components that reduce iron is of relevance to the “chelator-mediated Fenton mechanism” that has been advanced as a theory for the non-enzymatic degradation of wood by brown-rot fungi.

This study considers variations in hyphal load in decaying wood in the presence of the fungicides CuSO 4 and cyproconazole. Variations in the chitin content of hyphae following exposure to both fungicides have been detected. Increasing concentrations of CuSO 4 and cyproconazole in wood caused an increase in the amount of N -acetyl glucosamine in the mycelia of Coriolus versicolor and Gloeophyllum trabeum , which may be associated with increased deposition of chitin. This may in turn be an expression of the formation of a thicker cell wall at increased fungicide concentrations. Low concentrations of both fungicides also caused an increase in the amount of mycelium produced by G. trabeum . However, the same concentrations were effective at preventing mass loss, indicating that the fungal mycelium was less effective at decaying wood, despite being present in relatively large amounts. In the case of C. versicolor , this effect was not observed, as increasing concentrations of both fungicides caused an initial decrease in the amount of mycelium, followed by a recovery phase at intermediate chemical concentrations. Again, mass loss was greatly inhibited by the presence of low concentrations of both fungicides.

The natural durability of larch wood is described as being highly variable, ranging from non-durable to durable. In this study, FT-NIR spectroscopy was investigated for its ability to predict the natural durability of commercially available larch wood. Samples originated from approximately 60 European and 25 Siberian larch trees, provided by three Austrian-based wood industries. Natural durability tests were performed using the test fungi Gloeophyllum trabeum and Coniophora puteana. FT-NIR spectra were recorded and average spectra were calculated for calibration modelling. The models were strong [R 2 (CV)=70.7–95.19, RMSEP=0.063–0.026] and showed better suitability with spectra acquired from radial surfaces compared to those from axial surfaces. The prediction model was valid across larch species (European and Siberian), so that exact knowledge of the growth and site conditions was not required.

Bacillus cereus is the only pathogen that is occasionally found in paper and paper products, but there is no information on its prevalence. The aim of this work was to obtain data for a risk assessment of B. cereus in cellulosic fibre-based products. Handsheets were formed using laboratory papermaking equipment from stocks admixed with B. cereus. Then the distribution of B. cereus and its heat-stable toxin, cereulide, between the fibre web and the wire filtrate was measured. The handsheets retained 5% of the vegetative cells and spores of B. cereus and 10–15% of the cereulide. Transfer of cereulide into food or drink through contact with paper was investigated using ethanol and hot and cold water as food and drink simulants. Less than 0.2% of the cereulide from handsheets was recovered from hot and cold water, as measured by LC/MS and the boar sperm bioassay. Total immersion in 95% v/v ethanol leached nearly all cereulide present in the paper. The results obtained with the bioassay were equivalent to those obtained by LC/MS for the leachates, indicating that cereulide retained its toxicity through the handsheet-making process. The results indicate that cereulide in pulps is probably also present in paper products made from them, but the concentration appears to be too low to be relevant in terms of toxicity.

The residual wood meal left after extraction of milled wood lignin (MWL) was extracted with lithium chloride/ N , N -dimethylacetamide, which is a well-known cellulose solvent, to afford a soluble fraction (cellulose-lignin fraction; CL) in 36.7% yield. The UV elution curve of CL acetate has the same profile as its refractive index (RI) elution curve. After partial degradation of CL by cellulase, the UV elution curve of CL acetate shifted to the low-molecular-mass region in a similar fashion as its RI elution curve. These results indicate that the lignin in CL (CL lignin) is chemically bonded to cellulose. On the other hand, half of the CL lignin was removed by xylanase treatment. It was concluded that approximately half of the CL lignin existed as a lignin-cellulose-xylan complex.

A lignin-carbohydrate complex (LCC) fraction isolated from the residue of milled wood lignin extraction of birch was found to form self-aggregates in water. The aggregates had relatively strong hydrophobic domains, comparable to the hydrophobicity of 80% ethanol. Dynamic light scattering analysis showed that the aggregates were transformed into small particles by sonication with a number-average diameter of 43.7±9.6 nm, and were stable in water. The surface pressure (π)-surface area ( A ) profile showed that the LCC also formed a monolayer on the water surface. Based on these results, we suggest that the LCC is amphiphilic in nature, despite its insolubility in low-polarity organic solvents.

The spatial arrangement of polymers in Sitka spruce ( Picea sitchensis ) was investigated by NMR proton spin-diffusion studies, supplemented by deuterium-exchange experiments monitored by FTIR spectroscopy. The FTIR spectra of earlywood sections after vapour-phase exchange with deuterium oxide showed that 43% of the hydroxyl groups were accessible to deuteration. This value is lower than predicted in the absence of aggregation of cellulose microfibrils into larger units, but greater than the predicted level of deuteration if 3.5-nm microfibrils surrounded by hemicellulose sheaths were aggregated into 4×4 arrays without space for deuterium oxide to penetrate between the microfibrils. The rate of proton spin diffusion between lignin and cellulose was consistent with the presence of microfibril arrays with approximately these dimensions and with lignin located outside them, in both earlywood and latewood. Proton spin-diffusion data for hemicelluloses were complicated by difficulties in assigning signals to glucomannans and xylans, but there was evidence for the spatial association of one group of hemicelluloses, including acetylated glucomannans, with cellulose surfaces, while another group of hemicelluloses was in spatial proximity to lignin. These data are consistent with a number of nanoscale models for the Sitka spruce cell wall, including a model in which glucomannans are associated with microfibril surfaces within the aggregate and water can penetrate partially between these surfaces, and one in which all non-cellulosic polymers and water are excluded from the interior of each microfibril aggregate.

In 2000, salt precipitates were found on surfaces of the Swedish warship Vasa , accompanied by low pH values, partly as a result of oxidation of accumulated sulfur compounds. One hypothesis is that oxidation of the sulfur compounds was catalysed by the large amounts of diverse iron compounds present in the wood. It is therefore of interest to develop a method to extract the iron compounds and simultaneously neutralise the acids. The iron compounds could be extracted using an aqueous solution of ethylenediimino-bis(2-hydroxy-4-methylphenyl)acetic acid (EDDHMA) or diethylenetriamine penta-acetic acid (DTPA) at alkaline pH, leaving only small amounts of iron compounds. The polyethylene glycol (PEG) used as the conservation agent, salts and other water-soluble compounds were co-extracted. The extraction rate was enhanced by stirring and by higher concentrations of the chelator, but diffusion of compounds through the wood was the most important factor for the overall extraction efficiency. Extraction of iron compounds from deep inside the wood is time-consuming and may take years. The results from this study imply that aqueous extraction with strong chelators at relatively high pH, 9–11, effectively removes iron compounds and neutralises the acids present. Although the results are promising, it is still too early to start major re-conservation of Vasa wood using extraction, as all the effects on the wood are not known, but such studies are in progress.

At present, ozone is one of the main chemicals in elemental chlorine-free (ECF) and totally chlorine-free (TCF) bleaching sequences. High consistency (HC) and medium consistency (MC) technologies are in use. This study shows that HC ozonation of hardwood kraft pulp, as expressed by the overall kappa number encompassing both hexenuronic acid groups and residual lignin, is a two-phase path. The reaction rate of the first phase is two- to three-fold higher than that of the second phase. We propose that the first phase is due to ozonation of both hexenuronic acid groups and residual lignin, whereas the second phase involves only residual lignin. The fiber width and wall thickness were relatively unchanged during ozonation. These results are in contrast to the “shrinking core kinetic model” frequently discussed in the context of HC ozonation. The development of pulp brightness and the decrease in pulp viscosity with the ozonation time are well correlated with the overall kappa number or the kappa number due to residual lignin alone.

In situ imaging nanoindentation was used to characterize the mechanical properties of pure paint films on eight types of plywood-based flooring with different wear resistance. Correlation between the mechanical properties of paint films and the wear resistance of wood-based floorings was investigated. The average modulus of elasticity (MOE) and hardness of the paint film tested were 3.33–5.77 and 0.19–0.34 GPa, respectively. A strong linear relationship (r 2 =0.87) between the MOE and hardness of the paint film was found. Neither of these properties was directly correlated to the macro wear resistance of the floorings. Moreover, the composite index H 1.5 E -1 – frequently used as an indicator of wear resistance in materials science – was not useful either in evaluating the wear resistance of wood floorings. However, in situ imaging nanoindentation was suitable for characterization of the mechanical properties of paint films, although this technique was not suited for direct evaluation of the wear resistance of wood floorings.