Volume 77, Issue 9

Planting spacing plays an important role in tree growth and wood formation. Thus, the aim of this study was to determinate how planting spacing and genetic material affect the radial variation of basic density and chemical composition of wood. The sampling of this study was based on 4 clones of Eucalyptus urophylla × Eucalyptus grandis at 5 years of age planted in four spacings (3 × 1, 3 × 2, 3 × 3 and 3 × 4 m). To determine the basic density (BD), extractive (EXT) and lignin (LT) content, wood discs were removed at breast height, which were sectioned in three radial positions (pith, intermediate and sapwood). The results showed that genetic material, planting spacing and radial position affected the values of BD, EXT and LT content. The BD and EXT content tended to increase with increased planting spacing, while the LT content tended to decrease. In relation to the radial variation, the basic density showed an increase in the pith-bark direction, while the EXT content showed a decrease in this direction. For LT, no significant difference was observed in the pith-bark direction. In general, the largest planting spacings promoted the highest rates of variation of the properties studied.

Plantation forest species were introduced into South Africa due to limited availability of native forests for wood-derived products. Currently, the Mexican pine species, Pinus patula, is the most widely planted softwood species in the country. To study the effect of growth environment on wood and processing properties for the species, sample plots were established in a 20-year rotation covering a wide range of soil geologies and altitudes in Mpumalanga, South Africa. Temperature and seasonal rainfall were also determined for the sample plots. Randomly selected sample trees were harvested from the plots and processed at a plywood plant to determine veneer recovery and quality. Trees grown on sites composed of granite soils, with higher annual maximum temperatures and less rainfall, found in the Highveld region, displayed superior tree size, slenderness, and volume growth, compared to trees grown on dolomite and shale soils common to the Lowveld region. Veneer derived from Lowveld trees had more splits which were largely related to defects. Larger trees also had a greater percentage volumetric heartwood and a smaller live crown, compared to smaller trees. Highveld trees had greater net veneer recovery and produced better quality veneer than trees grown on the Lowveld. In the Mpumalanga forestry region, strong co-relatedness exists between soil geology, altitude, and climate. Although tree form and wood properties were found to differ with varying soil geology and altitude, these differences were primarily related to climate rather than soil properties. These findings highlight the pitfalls associated with neglecting either climate or soil properties when analysing site-specific growing conditions on tree growth and form.

Using a Berty-type CSTR reactor, Ji (2007. Kinetics and mechanism of oxygen delignification , Ph.D. thesis. The University of Maine) obtained oxygen delignification kinetics first order in lignin when neglecting the higher initial delignification phase. In the present study the same Berty/CSTR reactor with an improved temperature control was used to determine the oxygen delignification kinetics of Southern Pine kraft pulp, with the kinetics now corrected for lignin removed by oxygen-free alkaline leaching. This removes the initial high delignification rate peak so that the kinetics over the entire lignin range can be modelled as first order in “reactive” lignin, which is lignin corrected for a small amount of unreactive lignin. It suggests that softwood pulp oxygen delignification consists of two contributions; phenolic delignification and alkaline leaching. The initial alkaline leaching phase is mathematically described by semi-infinite alkaline diffusion of dissolved lignin trapped in the cell wall after pulp washing. For phenolic delignification, the reaction orders in alkali concentration and oxygen of the power law delignification equation are 0.3 and 0.44 respectively, while the activation energy is 63 kJ/mol. Taking into account the unreactive HexA, the small amount of unreactive lignin, and the lignin removed by alkaline leaching, the kappa number is well predicted by the new delignification kinetics.

Microscopic X-ray computed tomography (XµCT) aided finite element (FE) modelling is a popular method in material science to relate material properties to heterogeneous microstructures. Recently, a methodology was developed for the XµCT aided FE modelling of wood, which characterises the process from specimen preparation to estimation of material properties. In the current research, this methodology is tested on branches of Norway spruce ( Picea abies (L.) Karst.) to estimate the hygroexpansion coefficients of opposite (OW) and compression wood (CW). These properties are largely unknown and have engineering implications. The study is complemented by measurements of density, moisture content (MC) and elastic moduli. Results showed that the methodology assisted in the design of an integrated process and the identification of bottlenecks. It was seen that the level of detail of the numerical model had a strong influence on the obtained hygroexpansion properties. CW from branches showed higher density and longitudinal shrinkage coefficients, and elastic moduli less affected by MC. These differences are unlikely caused by MC, but more likely by the characteristics of the microstructure.

Thermally modified timber (TMT) reduces hygroscopicity, increases dimensional stability, and decay resistance. Although there is a substantial amount of research on heat-treated wood, investigations on the sensitivity of cell wall swelling behavior to water variation are limited. Therefore, this study focused on the swelling behavior of TMT from cellular and chemical perspectives. The effects of heat treatment on the hygroscopicity and swelling behavior of the wood cell walls were studied using dynamic vapor sorption and confocal laser scanning microscopy. Changes in the chemical composition and cellulose crystallinity were studied using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray diffraction. The results revealed that the hygroscopic swelling of latewood significantly decreased with increasing treatment temperature, reducing the anisotropy of the wood cell swelling. The hygroscopicity of wood was reduced by heat treatment, and a clear decrease in hysteresis was observed at elevated treatment temperatures. The FTIR spectra indicated that both hemicellulose and lignin were degraded. The crystallinity and lateral size of the cellulose increased after heat treatment. Similar changes in the chemical composition and crystallinity of cellulose were observed in the latewood and earlywood.

Conventional fluorescence spectroscopy has been suggested as a valuable tool for classifying wood species rapidly and non-destructively. However, because it is challenging to conduct absolute emission intensity measurements, fluorescence analysis statistics are difficult to obtain. In this study, another dimension of fluorescence, that is, fluorescence lifetime, was further evaluated to address this issue. A time-resolved fluorescence spectroscopic measurement system was first designed, mainly using a streak camera, picosecond pulsed laser at 403 nm, and a spectroscope, to collect the fluorescence time-delay (FTD) profiles and steady-state fluorescence intensity (FI) spectra simultaneously from 15 wood species. For data analysis, principal component analysis was used to “compress” the mean-centered FTD and FI spectra. Then, support vector machine classification analysis was utilized to train the wood species classification model based on their principal component scores. To avoid overfitting, ten-fold cross-validation was used to train the calibration model using 70 % of the total samples, and the remaining 30 % hold-out validation was used to test its reproducibility. The cross-validation accuracies were 100 % (5 softwoods) and 96 % (10 hardwoods), with test-validation accuracies of 96 % and 89 %.

Wood surface charring is a treatment method commonly employed to enhance weather protection and aesthetic appearance of building exteriors. This study aims to investigate the differences between two wood surface charring processes: the traditional Japanese method known as Yakisugi and an alternative charring technique industrially manufactured with a gas burner. The objective of the study was to assess whether a thicker layer after Yakisugi treatment has any advantages over a thinner layer after the alternative process. Vibrational spectroscopy techniques including UV resonance Raman (UVRR) and Fourier transform infrared (FTIR) spectroscopy, were utilized in conjunction with X-ray-micro-CT analysis. The findings revealed that ATR-FTIR spectroscopy detected the degradation of carbohydrates and changes in lignin within the charred surface, although both processes exhibited similar vibrational contributions. In contrast, UVRR spectroscopy provided insights into the carbonized layers, revealing spectral differences indicating variations in temperature during the charring processes. X-ray micro-CT analysis visually highlighted significant differences in the coal layers, suggesting distinct combustion profiles. Remarkably, the macrostructure of wood treated with Yakisugi remained intact despite a thicker charred layer compared to the alternative charring techniques. However, further investigations are required to assess the weather stability of the alternative charring method for a comprehensive understanding.

Common tissue paper manufacturing trends aim at partial or total replacement of softwood pulp with hardwood pulp for its production, such as bleached eucalyptus kraft pulp (BEKP), in order to optimize the process and the final product properties such as softness. However, the use of a single type of hardwood fiber results in lower strengths of both wet and dry webs. To maintain necessary strength and desired properties, the incorporation of several additives is often required. In this context, low molecular weight polyethylene glycol (PEG) and different wet strength resins, such as polyamideamine-epichlorohydrin (PAE) and glyoxalated polyacrylamide (GPAM) resins, were combined to achieve an innovated product with improved properties. In particular, wet and dry tensile strength was significantly improved when combining PEG and wet strength resins, especially observed in tissue papers prepared with PAE resin, high-charge cationic agent and bulk applied aqueous PEG solution. Noteworthy that water absorption capacity and softness of tissue paper were not critically affected by PEG incorporation, regardless of application method used (in bulk or by spray).