Volume 12 Issue 4

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.

Relationships between fiber surface chemical components and the efficiency of chlorine dioxide bleaching were studied using chemical analysis in combination with attenuated total reflectance-Fourier transform infrared spectrscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The amount of surface lignin decreased quickly at the beginning of the bleaching, and the brightness increased during the bleaching. Surface oxidation took place immediately, and the amount of lignin on the fiber surface decreased during the bleaching, especially in the first 5 min. The ratio of aromatic carbons to aliphatic carbons also decreased, which indicated that the lignin was degraded and new aliphatic carbons formed that might noticeably deposit on the surface of the fiber. The aliphatic carbons reacted with the in-situ formed hypochlorous acids, and thus affected the bleaching efficiency. Further bleaching led to the deposition of more acidic functional groups on the fiber surface with increased acidity-basicity ratios, which also affected the whole efficiency of bleaching.

A laser shock tensioning process is proposed in this work for circular saw blades. To explore the tensioning stress formation mechanism of the laser shock tensioning process, a theoretical model was built based on a finite element method utilizing reasonable simplifications and assumptions. By comparing theoretical analysis and the measured results, the theoretical model proved to be correct and the laser shock tensioning process proved feasible. The effect of the dynamic yield strength of the circular saw blades on the laser shock tensioning process was studied. Simulation results showed that the dynamic yield strength of the circular saw blades exhibited a strong effect on the overall tensioning. Circular saw blades with a higher dynamic yield strength can obtain greater room for improvement via the tensioning effect.

A 3-axis parallel kinematic machine tool and advanced control system with programming in G-code for the milling of wood material are described in detail. This parallel kinematic machine is based on a 3-PSS (prismatic link, spherical link, and spherical link) parallel mechanism. A programming system and control based on a real-time PC windows platform and Mach3 software system was implemented for this tool. Finally, a model application of a programming system developed for a three-degree-of-freedom linear delta parallel machine was presented, and the workability for milling wood material (medium-density fibreboard) was shown.