Volume 9 Issue 2

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.

An ultra-low density fiberboard was made of plant fiber using a liquid frothing approach. The inflammability of the plant fiber limited its application as a candidate for building insulation materials and packaging buffering materials. Si-Al compounds were introduced into the foaming system because of the high temperature resistance of Si and Al compounds. The results from energy-dispersive spectroscopy suggested that the Si and Al relatively evenly covered the surface of the fibers, and their weight ratios in the material increased as a function of the amount of Si-Al compounds. The increasing weight ratios of Si and Al affected the fire properties of the material, reducing the released amount of heat, smoke, and off-gases such as CO and CO2, as well as decreasing the mass loss percentage, shown through the use of a Cone Calorimeter. It follows that Si-Al compounds have an evident collaborative effect on the halogen fire retardant. The system can effectively restrain the fire hazard intensity and the yields of solid and gas volatiles.

Currently, marine protein byproducts are mainly hydrolyzed and prepared for applications that depend on their physiological activity. Such uses require strict removal of heavy metal ions from the material. In this work, a green approach was proposed using peanut shells as adsorbent to remove Pb(II) from solutions containing amino acid and sodium chloride. The effects of amino acids and sodium chloride on the removal of Pb(II), as well as the influence of liquid to solid ratio, pH, temperature, and contact time on the adsorption, were studied. The results showed that the content of sodium chloride and amino acid could significantly decrease the adsorption efficiency for Pb(II). The experimental data could be described with the Langmuir adsorption isotherm model and pseudo-second order kinetic model. The adsorption capacity of the sorbent for Pb(II) was calculated from the Langmuir isotherm model and found to be 7.1 mg g^-1 at pH 4.

The present work used a combined approach of oleic acid (OA) impregnation and thermal modification to improve the hydrophobicity and dimensional stability of southern pine (Pinus spp.). The wood samples were first treated with OA at a concentration of 5 or 10%, and then underwent thermal modification at 160, 180, or 200 °C. Thereafter, the water-related properties of modified wood including water absorption (WA), equilibrium moisture content (EMC), and volumetric swelling (VS) were investigated. Alterations in cell wall structure and chemical components were analyzed by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), based on the mechanisms discussed. While the results showed that both OA-treatment and thermal modification can each improve the water repellency and dimensional stability of wood, the combined system proved to be more effective. The synergistic increase of water-related properties was assumed to be caused by OA increasing the hydrophobicity of thermally modified wood as well as accelerating the decomposition of hydrophilic wood components during thermal modification. This assumption was supported by both SEM and FTIR results. Therefore, this research provides an approach for improving the accessibility to the energy-efficient thermal modification.