Volume 77, Issue 1

Plantation forests were originally established in South Africa to meet an increasing demand for solid wood products as there was a limited supply from native forests. The majority of the commercial softwood plantations were established with Mexican Pinus patula . Since growing conditions are known to impact tree growth, tree form, and wood quality of P. patula , sample plots were established over a cross-section of plantations in the Lowveld Escarpment and Highveld forestry regions of South Africa that covered an array of geologies and altitudes. Each sample plot was classified according to soil properties, rainfall, and temperature, and trees within the plots were measured for growth, form, and wood properties. Soil, growing days, and temperature were found to have little impact on tree form and wood properties. However, rainfall and specifically, spring rainfall, was found to have a highly significant impact on late wood formation, proportion of juvenile core, and wood density. In addition, tree height was found to be strongly correlated with maximum annual temperature.

Branches remain in the forest environment as logging activity residue. Considering the large size of many Amazonian trees, their branches have considerable dimensions and can contribute to a sustainable wood alternative for various applications. Due to the formation of reaction wood in the branches, relevant macro and ultrastructural changes can occur in its characteristics in relation to the trunk wood. However, the woods of the branches are not technologically well known. Therefore, this work aimed to evaluate the wood quality of branches of  Hymenaea courbaril L., comparing it with wood of trunks. The extractives and lignin contents, basic density, shrinkage, fiber biometry, microfibril angle and mechanical resistance to compression parallel to the fibers were analyzed. The branch wood had smaller fiber dimensions and a higher microfibril angle than the trunk wood. The basic density was similar between these materials. The linear and volumetric shrinkages were smaller in the branch wood than in the trunk, while the axial shrinkage was higher in the branch. The parallel compressive strength was also lower in the branch wood than in the trunk. The branch wood has properties suitable for products with higher added value such as furniture, decorative objects, floors and utensils in general.

Heat treatment is effective in reducing moisture absorption and improving the dimensional stability of wood. Low point metal alloy (LMPA) is characterized by high thermal conductivity and large surface tension and can be used as a liquid heat medium for heat treatment. To investigate the effects of liquid and gaseous heat medium on the hygroscopicity, dimensional stability, and chemical structure of heat-treated wood, LMPA and moist air were used as the heating medium during the heat treatment at 140 °C, 170 °C, and 200 °C for 2 h. The results indicated that LMPA heat treatment effectively improved the dimensional stability of wood by increasing the actual heat treatment temperature and reducing the preheating time of the wood. LMPA heat treatment at 200 °C decreased the radial, tangential, and volumetric swelling coefficients of wood by 62, 55, and 56%, respectively. Compared with moist air heat treatment, the radial, tangential, and volumetric swelling coefficients of the wood were reduced by 37, 27, and 38%, respectively. Chemical analyses via attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray diffraction (XRD) demonstrated that the LMPA heat treatment increased the degradation of hemicellulose and reduced the number of hygroscopic groups, resulting in higher crystallinity and enhanced dimensional stability. Hence, LMPA heat treatment can effectively resolve the poor thermal degradation due to prolonged preheating stage and high energy consumption associated with external power for forced convection during the conventional heat treatment using a gaseous heat medium.

Scots pine sapwood ( Pinus sylvestris L.) was modified with an aqueous solution of sorbitol and citric acid (SorCA) and a commercial phosphorus-based fire-retardant (FR). The aim of this study was to assess whether the fire behavior can be improved when the SorCA solution is supplemented by an FR and if this effect is resistant to leaching. The fire behavior of modified wood was investigated by a Bunsen burner ignition test, mass loss calorimetry (MLC) and thermogravimetric analysis (TGA). The results demonstrated a significantly improved fire-retardancy based on a decreased burning rate and a reduced mass loss in the Bunsen burner test. Also, the induced formation of a protective char barrier facilitated by the addition of a FR, reduced the heat release rate and delayed the ignition. The fire-retardant effect was still observed, to the less extent, after a cold-water (EN 84 2020) leaching of the specimens.

Although fungal bioleaching with Aspergillus niger has been investigated to remove metal from treated wood wastes, toxicological concerns limit the practical use of the species, necessitating the search for non-toxic species with comparable or greater metal removal efficiency. The removal of metals from wood treated with chromated copper arsenate (CCA) and copper amine-based preservatives was investigated using the non-ochratoxigenic mold Aspergillus tubingensis in comparison to A. niger via bioleaching. Metals were bioleached for 10 days by immersing treated wood sawdust in fungal culture filtrates. Culture filtrates were prepared by growing fungi in malt extract (ME) and sucrose media and then filtering the fungal biomass. Oxalic acid and citric acid were the predominant organic acids in A. tubingensis culture filtrate in ME and sucrose media, respectively. Citric acid present in sucrose media was found to be a more effective leaching agent for metals from preservative-treated wood. Citric acid produced by A. tubingensis and A. niger in sucrose media removed nearly 95% of copper, 80%–85% of chromium, and arsenic from CCA-treated wood, and 80%–90% of copper from wood treated with copper amine-based preservatives. As a result of its non-toxigenic characteristics and high metal removal efficiency, A. tubingensis may be a useful fungus for bioleaching metal components from inorganic preservative-treated wood.

Dehydrogenation polymer (DHP) is widely used as a model polymer of lignin. The chemical structure of DHP is highly affected by the synthesis conditions; however, the factors affecting DHP structure are not comprehensively understood. In this study, guaiacyl DHPs were synthesized to investigate the effects of reaction scale, pH, polymerization-enzyme activity, reaction media containing organic solvent, and differences between Zutropf (ZT) and Zulauf (ZL) modes on DHP properties. The DHPs were structurally characterized by size exclusion chromatography, 1 H- 13 C HSQC NMR, and thioacidolysis with and without Raney nickel desulfuration. In ZT mode, smaller reaction scale significantly increased β- O -4 content, and β- O -4 formation was negatively correlated with the dose of polymerization-enzyme, horseradish peroxidase. Acidic condition (pH 4.0) in succinate buffer also increased the β- O -4 content of the DHP, although the α position of the DHP was acylated by the incorporation of succinic acid. DHPs prepared at pH 9.0 had high β-1 contents and low β-5 contents, while the reaction in 20% 1,4-dioxane markedly increased the molecular weight of the DHP. A systematic approach controlling the molecular structure of DHPs would increase their value as models for native and isolated lignins.

Bamboo is susceptible to moisture-induced dimensional instability and cracking. Combining traditional methods with vascular bundle detection, the coordinates and fiber sheath area of each vascular bundle was determined accurately. Based on data fitting, the change in the shape of cross-section was quantified and analyzed based on parameters such as radius, radian, and arc length. The changes in the total area and the areas of different types of fiber sheath, as well as the changes in the arrangement of vascular bundles were studied. The results showed that when the moisture content was reduced from 64% to 0%, the radius of the cross section was increased by 21%, while the radian and arc length decreased by 22% and 6%, respectively. The fibers shrunk by 15%, which was greater than that of the other tissues except bamboo fibers (9%). The gradient distribution of the fiber volume fraction contributed to its asynchronous dry shrinkage. Significant radial and tangential displacements were found in vascular bundles. This work further elucidated the dry shrinkage mechanism of bamboo, and was of great significance for the quantitative analysis of changes in bamboo structure from a combination of micro and macro perspectives.