Research Articles

The in situ imaging nanoindentation technique was used to investigate the effect of age, culm height, and radial position on the cell wall mechanical properties of bamboo (Dendrocalamus farinosus) along the longitudinal direction of culms. The results indicated that among our four-sampled culm ages, the fiber cell wall had average values for the elastic modulus (MOE) and hardness (HL) of 18.56 GPa and 410.72 MPa, respectively. The ages of the culm had no significant effect on the observed MOE and HL among the 2-, 3-, 4-, and 5-year-old D. farinosus test specimens, with similar results observed at three different culm heights and radial positions. Furthermore, longitudinal MOE and HL values along the thickness of the cell wall were uneven, with average values for the middle lamella and the edge near the cavity only 20.97% to 29.78% and 9.22% to 31.71%, respectively, of the values found in the cell wall.

Reducing sugars contained in agricultural residue hydrolyzates can potentially be utilized in microbial fermentations to produce biofuels and biogas. Different types of agricultural residues were employed for photo-fermentative bio-hydrogen production, and the cumulative hydrogen production data fit well to the Modified Gompertz Model. Corncob was determined to have the highest reducing sugar yield and cumulative hydrogen production (12.64 mg mL^-1 enzymatic hydrolysate, 228.94 mmol L^-1) and maximum hydrogen production rate (5.9677 mmol L^-1 h^-1). Enzyme reuse was investigated by single factor experiment design to reduce the cost of bio-hydrogen production. Taking reducing sugar yield and activity recovery efficiency as reference, substrate re-adsorption method at different temperature and time, then enzyme immobilization method at different load and pH were investigated in the process of enzymatic hydrolysis. The efficiency of enzyme utilization was enhanced via substrate re-adsorption and enzyme immobilization methods, which resulted in a 4-fold increase in recycling efficiency. The optimal enzyme reuse condition by substrate re-adsorption was a re-adsorption time of 90 min at a temperature of 15 °C, while the optimal condition by enzyme immobilization method was a pH of 4.8 and immobilized enzyme load of 400 mg.

The aim of this study was to eliminate the problems of hardness, gloss, and color change of some wood materials exposed to weathering conditions using a bleaching procedure to attempt to return the wood material to its natural state. For this, wood samples of Scots pine (Pinus sylvestris L.), Eastern beech (Fagus orientalis L.), sessile oak (Quercus petraea L.),and chestnut (Castanea sativa Mill.) were exposed to weathering conditions based on 12 months ASTM D-1641, followed by a bleaching procedure using 18% solutions of S1 (NaOH + H2O2), S2 (NaOH + Ca(OH)2), S3 (KMnO4 + NaHSO3 + H2O2), S4 (NaSiO3 + H2O2), and the commercial product S5 (Cuprinol Decking Restorer- (H2C2O4 + C2H4(OH)2). The color, gloss, and hardness changes of samples were determined according to ASTM D 2244-2, EN ISO 2813, and ASTM D 2240 standards. As a result, hardness and gloss values of all woods decreased due to weathering conditions and the wood color turned grey due to degradation. When comparing the weathered samples to the bleached samples, the hardness value was found to be highest in pine wood bleached with the S2 solution, and the gloss value was highest in oak wood bleached with the S1 solution. The greatest color change was found in pine, beech, and chestnut samples bleached with the S4 solution and in oak samples bleached with the S1 solution.

In this study, the electromagnetic (EM) performance of rice husk ash (RHA) calcined from rice husk was evaluated. Porous RHA with a bulk density of 0.4 g cm-3 is mainly composed of carbon and silica. The degrees of surface melting and destruction of porous structure increase with ashing temperature, while a nitrogen atmosphere retards surface melting and destruction because of the retention of carbon. A temperature of 700 °C is the lower limit for achieving significant surface melting, whereas 800 °C in air will destroy the porous structure and conductive network formed by surface melting. All RHA samples showed low permeability values caused by the absence of magnetic components. Sufficient conductive carbon and the formation of conductive networks are prerequisites for reasonable complex permittivity values. The calculated EM wave absorption of RHA achieved a maximum reflection loss (RL) of −21 dB at 2 to 18 GHz, including 5 GHz with an RL < −10 dB, which is above the average of traditional absorbers. This study reveals a new approach for fabricating an EM wave (microwave) absorber with low density and strong absorption by using agricultural wastes as starting materials.

Activity levels of extracellular hydrolytic enzymes produced by Stenocarpella maydis, a fungal pathogen of maize, have so far not been reported. Production of xylanase, cellulase, and acid protease by this ascomycete using different culture media in solid-state and submerged fermentation was studied. In solid-state fermentation, polyurethane foam was used as an inert support, and corncob, corn leaves, and broken corn were used as biodegradable supports. The highest xylanase activity was produced in the medium with xylan in both fermentation systems, reaching 18,020 U/L and 19,266 U/L for submerged and solid-state fermentation, respectively. Cellulase production was observed only in the culture medium with carboxymethylcellulose, obtaining values of 7,872 U/L in submerged fermentation and 9,439 U/L in solid-state fermentation. The acid protease was produced only in minimal medium with glucose in acidic pH, reaching the highest levels of activity in SSF (806 U/L). The corncob was the best biodegradable support for the production of xylanases and acid protease. Two isoenzymes of xylanase and cellulase were observed in both fermentation systems, and three isoenzymes of xylanase were produced on the biodegradable supports.

A high molecular-weight thermoplastic lignin-based polymer was successfully synthesized by adjusting the degree of polymerization while inducing linear growth of lignin macromers via methylene diphenyldiisocyanate. The thermoplastic lignin-urethane polymer was desirably achieved in a narrow range of reaction conditions of 2.5 to 3.5 h at 80 °C in this study, and the molecular weight of the resulting lignin-based polyurethanes (LigPU) reached as high as 912,000 g/mole, which is far above any reported values of lignin-based polymer derivatives. The thermal stability of LigPU was greatly improved by the urethane polymerization, giving the initial degradation temperature (T2%) at 204 °C, which should be compared with T2% = 104 °C of the pristine lignin. This was due to the fact that the OH groups in the lignin macromers, having low bond-dissociation energy, were replaced by the urethane bonds. In dielectric analysis, the synthesized LigPU exhibited a softening transition at 175 °C corresponding to a combinatorial dual process of the dry Tg,dry of the lignin macromers and the softening of methylenediphenyl urethane chains. This work clearly demonstrated that a high molecular weight of thermoplastic LigPU could be desirably synthesized, broadening the lignin application for value added and eco-friendly products through common melt processes of polymer blend or composites.

The present study deals with the physical and mechanical properties of dry-formed medium density fibreboard (MDF) made from renewable biomass kenaf (Hibiscus cannabinus L.) stem as a function of adhesive level and refining conditions. Raw material was prepared by heating for 5 min at pressure levels of 6 and 8 bars. Experimental samples with a target density of 700 kgm-3 were produced with 10, 12, or 14% urea formaldehyde as a binder. Physical properties of MDF panels, such as thickness swelling (TS) and water absorption (WA) as well as mechanical properties including modulus of rupture (MOR), modulus of elasticity (MOE), and internal bonding (IB), were evaluated. Based on the test results, resin content and refining pressure have significant effects on the physical and mechanical properties of MDF panels. High resin content and pressure produced MDF boards with low WA and TS but high MOR, MOE, and IB. At 8 bars pressure and 14% resin content, the MDF recorded optimum WA (83.12%), TS (20.2%), MOR (25.3 MPa), MOE (3450 MPa), and IB (0.51 MPa).

In the present study, the fatty acid components of the wood, bark, and essential oil of wood from Delonix regia as well as its antibacterial, antifungal, and antioxidant properties were investigated for the potential ability to control plant and human pathogens. Myristic acid was found to be a major fatty acid in the wood and bark of Delonix regia, comprising 10.77% of wood and 9.63% of bark. According to the GC-MS results, naphthalene derivatives were detected in the essential oils from the wood samples. Heptadecane and acyclic hydrocarbons were found in a high percentage (14.05%). Methanol: chloroform (1:1 v/v) wood extract showed effective activity against Bacillus subtilis, Sarcina lutea, and Staphylococcus aureus, where the bark extract was most active against Escherichia coli. The essential oil showed good antibacterial activity against Pectobacterium carotovorum. The bark extract showed the maximum percentage inhibition of fungal mycelial growth against Penicillium selerotigenum (70.37%) and Paecilomyces variotii (77.78%), and the essential oil showed moderate inhibition against Aspergillus nigra (44.44%). The total antioxidant activity of essential oil, stem wood, and stem bark extract was 84.34%, 80.33%, and 70.21%, respectively.

TiO­2-treated acacia hybrid (Acacia mangium x auriculiformis) wood was fabricated by combined pressure-impregnation and hydrothermal post-treatment. The wettability and microstructure morphology, as well as the crystalline structure of the titanium dioxide (TiO2) gels of the TiO2-treated wood, were studied. Contact angle measurements of the blank wood and the TiO­­2-treated wood indicated a significant increase in hydrophobicity, with contact angles of above 150° in treated samples. Furthermore, the water-resistant property of the treated wood was quite stable, even after immersion in boiling water. Field emission scanning electron microscopy (FE-SEM) results showed that the microstructure morphology and the size of TiO2 gels on the wood surface were dependent on the pH of the post-treatment solutions. Additionally, the presence of amorphous TiO2 gels was indicated by X-ray diffraction (XRD) analysis. The results of this study indicate that combined pressure-impregnation and hydrothermal post-treatment can create a hydrophobic wood-TiO­2 composite.

Corn stover is an abundant feedstock in the US that can be used for second generation bioethanol production. However, there is little useful data on structure of the lignin of corn stover. The following principal tasks will be addressed to profile the structure of corn stover: (1) separation of corn stover into stem, cob, and leaf; (2) isolation of cellulolytic enzyme lignins (CEL) from extractive-free and the alkali-treated fractions; (3) quantification of p-coumarate and ferulate of fractions by HPLC. The results of alkaline nitrobenzene oxidation and 1H-13C HSQC NMR indicated: (1) the structure of lignin varied in the fractions; (2) a remarkable amount of p-coumarate and ferulate was identified and determined; (3) the remarkable structural changes of lignin induced by alkaline treatment were elucidated.