Volume 68, Issue 2

Chemically or physically modified wood materials have enhanced resistance to wood decay fungi. In contrast to treatments with traditional wood preservatives, where the resistance is caused mainly by the toxicity of the chemicals added, little is known about the mode of action of nontoxic wood modification methods. This study reviews established theories related to resistance in acetylated, furfurylated, dimethylol dihydroxyethyleneurea-treated, and thermally modified wood. The main conclusion is that only one theory provides a consistent explanation for the initial inhibition of brown rot degradation in modified wood, that is, moisture exclusion via the reduction of cell wall voids. Other proposed mechanisms, such as enzyme nonrecognition, micropore blocking, and reducing the number of free hydroxyl groups, may reduce the degradation rate when cell wall water uptake is no longer impeded.

Chemithermomechanical pulps (CTMP) were prepared from Eucalyptus globulus and photoirradiated, and the responses have been examined by means of ultraviolet (UV) microspectrophotometer. The absorbance in the UV spectra of fiber walls increased in the range of 300 of 350 nm as a result of photoirradiation, indicating the formation of conjugated double-bound systems in the fiber walls. These spectral changes occurred only on the irradiated surface of sheets. CTMP photoirradiation under various atmospheres indicated that the presence of oxygen in the irradiation atmosphere is not necessary for CTMP yellowing. In nitrogen or vacuum, photoyellowing was at the same level as observed under oxygen. This observation was interpreted as a result of direct elimination of proton radicals from free phenolic groups and/or cleavage of β-aryl ether linkages. This induced probably the excited triplet state of α-carbonyl structures in CTMP, which leads to chromophore formation in the absence of oxygen. Reduction of CTMP with sodium borohydride impeded effectively the effects of photoirradiation only in the absence of oxygen. On the contrary, acetylation of CTMP had no effect in the absence of oxygen but led to photobleaching in the presence of oxygen.

The environmentally benign closure of water systems in paper mills leads to the problem of accumulation of dissolved and colloidal wood substances (DCS) in process water. Notably, pitch affects the pulp and paper production negatively and increases the demand for additional treatment of the process water. In the present article, the purification of thermomechanical pulping process water from the alkaline peroxide bleaching stage has been investigated, with the induced air flotation (IAF) in focus. The following parameters were considered concerning the IAF efficiency to remove detrimental substances: concentration of cationic foaming agent, pH value, calcium concentration, and temperature. The amounts and characteristics of residual DCS were determined by gas chromatography and turbidity measurements. Residual concentrations of the foaming agent dodecyltrimetylammonium chloride were determined by electrospray ionization mass spectrometry. Up to 90% of pitch was removed, whereas hemicelluloses, which are important in preventing pitch problems, remained in the waters. Up to 70% of the pectic acids accounted for the high cationic demand of the process waters were removed by optimization of the IAF parameters. The presented separation process gives new opportunities to a selective purification of the process waters.

A combination of compression and heat treatment is a modification method that has great potential for improving the mechanical properties and dimensional stability of wood materials in industrial application. The objective of this project was to track changes in the microstructure, chemical composition, cellulose crystallinity, and mechanical properties of the treated poplar cell wall to investigate the mechanism of modification. Poplar boards were compressed at 100°C and subsequently treated in the hot press at 200°C. The results indicated that the treatment contributed to a reduction in porosity without obvious mechanical compression and damage to the cell wall. Hemicellulose degraded, however, and the relative lignin content and cellulose crystallinity increased during the process. The observed increase in relative lignin content and crystallinity may contribute to the improvement of mechanical properties. The longitudinal elastic modulus and hardness of poplar cell walls increased significantly from 12.5 and 0.39 GPa for the control to a maximum of 15.7 and 0.51 GPa for compressed wood with HT, respectively.

The temperature and moisture profiles during thermal modification of beech ( Fagus sylvatica L.) and spruce ( Picea abies L. Karst.) wood have been investigated. Specimens with dimensions of 80×80×200 mm 3 were heat treated based on ThermoWood technology. Heat transfer was continuously measured by several thermocouples placed into various positions of the samples. In the course of the treatment, samples were removed from the chamber at different times, and their moisture content (MC) was measured by the so-called slicing technique. The complete data of heat and moisture movement during the heat treatment process are presented. Significant temperature gradients occur in the initial and modification stages of the process. In the latter, the chamber temperature was 200°C for 3 h, but exothermic reaction increased the sample temperatures to 240°C (beech) and 215°C (spruce). Thermodiffusion (Soret effect) at the beginning of the process was observed. Therefore, the MC under surfaces (in transverse and in longitudinal direction) was increasing ∼0.5%–3% for 5 h. The results provide a better insight into details of thermal modification of wood.

A model has been developed aiming at the description of the effect of thermal modification on the electrical conductivity of wood. The intention was to calculate the moisture content (MC) of thermally modified timber (TMT) through the parameters electrical resistance R , wood temperature T , and CIE L * a * b * color data, which are known to correlate well with the intensity of a heat treatment. Samples of Norway spruce ( Picea abies Karst.) and beech ( Fagus sylvatica L.) samples were thermally modified in laboratory scale at 11 different heat treatment intensities and the resistance characteristics of the samples were determined. Within the hygroscopic range, a linear relationship between the resistance characteristics and the mass loss (ML) through the heat treatment was established. Based on this, a model was developed to calculate MC from R , T , and ML. To validate this model, color values of 15 different TMTs from industrial production were determined for estimation of their ML and fed into the model. MC of the 15 arbitrarily heat-treated TMTs was calculated with an accuracy of ±3.5% within the hygroscopic range. The material-specific resistance characteristics based on experimental data led to an accuracy of ±2.5%.

Spruce was submitted to high-temperature (150°C–170°C) refining for 2 or 5 min to produce thermomechanical pulp (TMP) fibers with decreased electrical energy consumption. The pulp was characterized in terms of specific energy consumption as well as tensile and surface properties. The fibers from high-temperature TMP contained more surface lignin even if all sample types usually broke at the S1–S2 cell wall region. They also produced significantly weaker paper sheets, whereas their dry zero-span strength did not suffer substantial losses, indicating decreased fiber-fiber bonding. Tensile strength properties were also determined of a bisphenol-A-epichlorohydrin-based epoxy resin mixed with 5% fiber as a test for fiber-matrix compatibility in composite applications. Based on these preliminary results, high-temperature TMP shows potential for composite reinforcement due to its lower tendency to aggregate and its better compatibility with the tested matrix material.

Strength grading is essential for the efficient use of structural timber. Although international standards exist for machine strength grading, visual grading is still regulated based on national rules, which are expected to allow safe and economic grading results. Although there are large differences in the graded output because the species, the cross section, and the origin of the timber influence the results, some of these standards are considered to be applicable universally. The present article demonstrates how the chosen standards influence the grading results. Depending on the parameters, the yields or the mechanical properties are low compared with the declared values. The results also show the efficiency and applicability of different national standards for strength grading of timber from various origins. Furthermore, it is recommended to reconsider the existing limits for source areas and cross sections given in the standard EN 1912.

Fast pyrolysis oil (Py-oil) from Cunninghamia lanceolata wood was the starting material in preparing alcohol-soluble phenol-formaldehyde (PF) resins. For this purpose, phenol (Ph) and Py-oils were mixed in weight ratios of 50/50, 40/60, and 30/70. The molecular weight distribution, thermal setting behavior, and heat resistance of the set resins were investigated. Albizia falcataria wood powder and cotton paper were impregnated with the resin mixture, and molding plates were produced by hot pressing; their physical, mechanical, and thermal properties were evaluated. The results show that Py-oil blended with Ph is a suitable raw material for preparing alcohol-soluble PF resins, which possess the characteristics of thermal melting and setting. The properties of the molding plates were satisfactory. The static bending strength (>100 MPa) and elastic modulus of the cotton paper-based products fulfill the requirements of CNS 10559 standard. The initial temperature of the thermal degradation of molding plates is >345°C. The performance of the molding plates decreased with increasing ratios of Py-oil.

Different enzymatic strategies were applied to improve lignin and hexenuronic acid (HexA) removal. Three laccases (L) with different redox potentials were applied in combination with 1-hydroxybenzotriazole or methyl syringate to softwood sulfite and hardwood kraft fibers. The enzymes with a high-redox potential from Pycnoporus cinnabarinus and Trametes villosa were found to be the most efficient. The bleaching efficiency was not significantly influenced by the presence or absence of HexA in the different types of lignocellulosic fibers. Subsequently, the lignin or HexA removal in the presence of different mediators was evaluated in eucalyptus fibers with the T. villosa laccase ( Tv L). Natural mediators removed only lignin, whereas the combinations of Tv L with synthetic mediators removed both HexA and lignin. The mediator violuric acid (VA) was the most efficient as judged by the properties of fiber and effluent. A xylanase pretreatment stage was found to boost the access of the L VA system to HexA without affecting lignin in the pulp.

Twenty-four Alternaria strains have been isolated from wood samples in Korea and submitted to phylogenetic analyses. The gene trees generated from the ITS and histone gene region sequences revealed that, among the genus Alternaria , two species, Alternaria alternata sensu lato (s.l.) and Alternaria tenuissima , are involved in wood discoloration. In addition, the histone gene was useful as a marker for differentiating between A. alternata s.l. and A. tenuissima .

Mild hydrogenolysis has been compared with thioacidolysis as a method for degrading lignins in situ and in isolated form before analysis by gas chromatography/mass spectrometry and quantitative 31 P nuclear magnetic resonance (NMR) spectroscopy. Both degradation methods gave similar levels of β-aryl ether-linked phenylpropane units that were released as monomers. Degradation by hydrogenolysis generally gave lower levels of total phenylpropane units when analyzed by 31 P NMR, especially in the case of lignins with high levels of condensed units. Overall, these results indicate that mild hydrogenolysis could offer an alternative to thioacidolysis for probing lignin structure.

Bamboo is one of the world’s fastest growing plants. They reach a final height of 15–40 m during a period of 40–120 days. The full height is reached by intercalary growth of each node. However, it is very difficult to detect the complex vascular system in a bamboo node using traditional methods. X-ray computed microtomography (μCT) is a noninvasive novel approach to the three-dimensional (3D) visualization and quantification of biological structures. In the present article, μCT has been applied to provide insights into the internal structure of bamboo node, where three branches are connected. The picture obtained could hardly be obtained by any other means. The bamboo nodal characteristics of three transverse and axial sections are presented. The complex 3D network of vascular bundles has been directly obtained for the first time.