Research Articles

Several different methods for the extraction, separation, and purification of wood constituents were combined in this work as a unified process with the purpose of achieving a high overall efficiency of material extraction and utilization. This study aimed to present a laboratory-scale demonstrator biorefinery that illustrated how the different wood constituents could be separated from the wood matrix for later use in the production of new bio-based materials and chemicals by combining several approaches. This study builds on several publications and ongoing activities within the Wallenberg Wood Science Center (WWSC) in Sweden on the theme “From wood to material components.” Combining the approaches developed in these WWSC projects – including mild steam explosion, membrane and chromatographic separation, enzymatic treatment and leaching, ionic liquid extraction, and fractionation together with Kraft pulping – formed an outline for a complete materials-biorefinery. The process steps involved were tested as integral steps in a linked process. The scale of operations ranged from the kilogram-scale to the gram-scale. The feasibility and efficiency of these process steps in a biorefinery system were assessed, based on the data, beginning with whole wood.

Cellulose nanofibers (CNFs) with an average diameter 8 nm were isolated from corncobs using a stepwise method that included steam-explosion pretreatment, alkaline treatment, sodium hypochlorite bleaching, high-speed blending, and ultrasonic treatment. This mechanochemical method used only two chemical reagents in low concentrations to remove non-cellulosic components. The removal of non-cellulosic components was confirmed by Fourier-transform infrared spectroscopy. X-ray diffraction revealed an increase in crystallinity during steam explosion and subsequent mechanochemical treatments. Pretreatment by steam explosion caused the partial hydrolysis of hemicellulose and loosened the structure of raw materials, which facilitated the subsequent chemical processes. The thermal stability and morphology of samples at different stages were also investigated. Steam explosion increased the thermal stability of hemicellulose and cellulose components, as it removed a fraction of hemicellulose. High-speed blending reduced the entanglement of cellulosic fibers and created uniform size. Ultrasonic treatment was used in the final step of nanoscale fibrillation. The method used in this study is environmentally friendly and has the potential to be applied at industrial scale.

In plywood manufacturing, the surface characteristics of veneers play a critical role in achieving appropriate bonding performance. An inactivated wood surface caused by oxidation or migration of wood extractives has been shown to lead to an insufficient bonding quality. In this study, inactivated birch and spruce veneer surfaces were activated with corona and chemical NaOH treatments. The effects of the treatments were determined by contact angle measurements and bond quality tests conducted with Automated Bonding Evaluation System (ABES). In addition, the mechanical properties of the plywood produced from the treated veneers were evaluated. The results showed that the corona treatment remarkably increased the wettability of the veneer surface and bond quality of both the spruce and birch veneers evaluated by ABES. The corona treatment also improved the mechanical properties of the birch plywood, but the spruce plywood properties were not affected as much. Soaking veneers in NaOH improved the wettability, but the bond strength was lower than that of the references.

Effects of heat and steam were investigated relative to the mechanical properties and dimensional stability of thermo-hygromechanically-densified sugar maple wood (Acer saccharum Marsh.). The densification process was performed at four temperatures (180 °C, 190 °C, 200 °C, and 210 °C) with and without steam. The hardness, bending strength, bending stiffness, and compression set recovery of the control and densified samples were determined. The effects of heat and steam on the density profile of the samples across thickness were also investigated. The results suggested that the effects of steam on the mechanical properties and dimensional stability of sugar maple wood were more important than that of heat’s influence. Compared to the samples densified without steam, the samples densified with steam showed higher values for hardness, bending strength, bending stiffness, compression set, and density, but much lower compression set recovery when treatment temperature was below 200 °C. High temperature combined with steam contributed to decreased compression set recovery. The lowest compression set recovery was obtained after the first swelling/drying cycle for all of the treatments. A higher weight loss occurred at 210 °C, which resulted in a noticeable decrease of wood density.

Dyes extracted from rengas (Gluta spp.) and mengkulang (Heritiera elata) wood were investigated as sensitizers in dye-sensitized solar cells (DSSCs). Three types of sensitizers, including individual sensitizer, mixture sensitizer, and co-sensitizer, exhibited different patterns of absorption properties under UV-Vis spectroscopy. The incident photon-to-current efficiency (IPCE) was analyzed via spectral response to examine the generation of photocurrent. Because mixture sensitized DSSCs obtained broader absorption spectra, they were expected to achieve good light harvesting and hence, enhanced photocurrent and conversion efficiency. The photovoltaic performance was further examined by electrochemical impedance spectroscopy (EIS). The mixture sensitized DSSCs exhibited good conversion efficiency (0.21% and 0.30%) compared with individual sensitized DSSCs (0.16% and 0.11%). The co-sensitized DSSCs also showed increased conversion efficiency with ruthenium (N719) dye as a co-sensitizer. The parameters calculated from EIS analysis were used to determine suitable conditions for the dye to be implemented in DSSC. The behavior of electron transport was determined to be efficient due to the increase of electron diffusion coefficient, electron lifetime, and low recombination rate as achieved by the mixture sensitized DSSCs.

Near infrared (NIR) spectroscopy was applied to conduct nondestructive measurements of water content in hardwood leaves. The authors developed a prediction method using a partial least squares regression (PLSR) analysis of NIR spectra data of six hardwood species. The pretreated spectra were compared by the full spectral range (1200 nm to 2500 nm) and short spectral ranges (1300 nm to 1600 nm [short range 1 (S1)] and 1800 nm to 2100 nm [S2]). Good prediction results were obtained for the full spectral range with six species. The correlation coefficient for prediction of each of the species ranged from 0.94 to 0.97, and the root mean standard error of prediction ranged from 1.59 to 7.72. Compared with the full spectral analysis, predictions based on S1 and S2 were less accurate. However, leaf water content could be predicted based on measurements in the S1 and S2 ranges. It was worth comparing the wavelengths in a preliminary experiment. In this research, NIR spectroscopy was a powerful nondestructive technique for determining the moisture content of tree leaves.

A β-xylosidase gene, xyl43C, from Clostridium clariflavum was heterogeneously expressed in Escherichia coli BL21. Xyl43C showed strong activity toward xylobiose, with specific activity of 76.6 U/mg and K_m of 4.97 mM. The optimal pH and temperature of Xyl43C were pH 6.0 and 60 °C, respectively. Xyl43C retained 94.4% activity after incubation at 55 °C for 1 h, and 75.4% at 60 °C for 1 h. It also showed xylose tolerance with IC₅₀ (half maximal inhibitory concentration) of approximately 100 mM. It nearly completely hydrolyzed 2 g/L of xylobiose at enzyme load of 2.51 mg/g xylobiose within 30 min and converted 40 g/L of corncob xylan into xylose at enzyme load of 1.48 mg/g xylan, with a yield of 60.9%. In conclusion, Xyl43C is an efficient xylose-tolerant β-xylosidase, with promising application potential in saccharification of xylan in biofuels industry.

The use of agricultural biomass to produce biofuels and energy can provide many environmental and socio-economic benefits. This research project examines the possibility of replacing part of the wood material in a pellet with various proportions of residues of agricultural crops such as medic, maize, wheat bran, wheat straw, sunflower, and cardoon. Such substitution would contribute to the recycling of materials and the sustainable use of wood and other natural resources. It would reduce emissions of gaseous pollutants by replacing the use of other fossil fuels with solid biofuels. The chosen agricultural species, as well as the beech wood used in this work, are among the most widely-available raw materials in Greece and Europe. Specifically, the higher heating value (HHV) of these materials, both separately and mixed, and their respective ash contents (%), a feature highly crucial for their future utilization as biofuels, were estimated and compared among species. Additionally, various mixing ratios of these materials were examined to determine the most appropriate pellet-type biofuels that meet the requirements of the corresponding international standards that pose restrictions on thermal efficiency and ash content.

The exploitation of Eucalyptus grandis lumber as structural material may take advantage of the finger-jointing and edge-gluing of the boards while they are still wet, so as to reduce the natural susceptibility of the species to warp and split during drying. But the strength grading needed for structural uses, usually performed on dried lumber, should be done before any gluing process, then already in wet condition. Thus, detection and assessment of selected properties of the wet lumber were evaluated. Eucalyptus grandis boards were measured by a multi-sensor machine soon after sawing, then dried and measured again. Destructive bending tests were then performed to determine the mechanical properties of the lumber and several predictive models were compared. The determination of non-destructive parameters by the machine was as effective on fresh as on dry lumber. The dynamic modulus of elasticity was the best single predictor of mechanical properties. In contrast, the knot parameter did not show a correlation between strength and stiffness robust enough to justify the efforts to measure it. Wet grading proved to be as effective as dry grading. Therefore, the study suggests that measuring only dynamic modulus of elasticity on fresh lumber is the best approach for the mechanical grading of Eucalyptus grandis.

Mechanical properties were investigated for millet husk (MH) fiber filled high density polyethylene (HDPE) composites. The chemical and thermal attributes of the fibers are also studied. The fibers were pulverized to 250 µm size. The composites were prepared by a melt blending technique using a Brabender® internal mixer, accompanied by hot compression. Composite formulations were based on; 10%, 20%, 30%, and 40% wt fiber loadings with 170 ^oC temperature, 10 min flow time, and 20 rpm rotational speed. Mechanical properties were obtained according to ASTM D3039, ASTM D790, and ASTM D256 for tensile, flexural, and impact test, respectively. Microstructures of fracture tensile test specimens were observed by SEM. Fiber chemical compositions were determined using acid detergent, neutral detergent, and acid detergent lignin to evaluate the cellulose, hemicelluloses, and lignin contents correspondingly. The percentages were 50.4% cellulose, 23.7% hemicelluloses, and 13.2% lignin with remains of other chemical constituents. Thermogravimetric analysis showed that the highest stable temperature was 245 ^oC. The tensile and flexural strength of the composites decreased with increasing fiber loading, while their modulus increased with increasing fiber loading. The impact strength was reduced drastically as fiber loading was increased. Therefore, it was concluded that millet husk fiber has potential to be used as raw material in composites applications.