Volume 8 Issue 2

Xylitol production from sago trunk cortex hydrolysate using Candida tropicalis was evaluated in shake flasks and a bioreactor. The fermentation and kinetic behaviours of this microorganism were investigated using sago trunk cortex hydrolysate and commercial xylose as substrate. Results obtained for sago trunk hydrolysate were close to the commercial xylose with xylitol yield of 0.82 gg^-1 and productivity of 0.39 gL^-1h^-1. The maximum specific growth rate, µmax for sago trunk cortex was higher (0.24 h^-1) compared to commercial xylose (0.17 h^-1). The bioreactor study showed an increase of about 6% (w/v) of xylitol concentration and 10% (v/v) of volumetric productivity when compared to the results obtained under the shake flasks, keeping xylitol yield above 0.8 g g^-1.

Membranes were prepared from alkaline lignin and poly(vinyl alcohol) (PVA) by a film casting method, and their properties were evaluated. These blend membranes can aptly be termed as green by nature as they are totally non-toxic and eco-friendly. The optimal mass ratio was determined based on the mechanical properties of membranes. The microstructure, mechanical properties, oxygen and carbon dioxide transmission, light transmittance, and thermal stability of the membranes were investigated. The blend membrane exhibited better thermal stability and barrier performance to oxygen and carbon dioxide than a PVA membrane due to the incorporation of alkaline lignin. Both tensile strength and elongation at break were increased with increasing mass fraction of alkaline lignin up to 15%, at which point the maximum of tensile strength and elongation at break were 43.65 MPa and 211.6%, respectively. The blockage of visible light at 600 nm was 62.36%, which was an improvement of 314.90% compared with the PVA membrane (13.36%). Based on this result, we suggest that the mechanical properties of blend membrane containing 15% alkaline lignin are excellent and better than PVA membrane (40.26 MPa, 179.37%). Thus, an alkaline lignin/PVA blend membrane was judged to be potentially suitable as an eco-friendly packing material.

Crofton weed stalk (CWS) was used as an adsorbent to remove methylene blue (MB) from aqueous solution. The adsorbent was analyzed by FT-IR and observed by SEM. The porosity and pHzpc were measured. The effects of adsorbent dose, initial dye concentration, solution pH, and solution temperature were investigated. Models of the adsorption kinetics and isotherms were analyzed, and thermodynamic parameters were calculated at different temperatures. The results showed that the adsorption capacity of MB on CWS increased with increasing initial concentration from 10 to 40 mg/L and pH from 2 to 7. The amount of MB removed increased as the adsorbent dosage was increased from 0.2 to 1.2 g/L. The maximum dye adsorption capacity of 28 mg/g was reached at around 120 min in a solution of 40 mg/L. A pseudo-second-order kinetic model described the kinetics well, and the experimental data followed the Freundlich model. The calculated values of standard free energy (ΔG^o) and standard enthalpy (ΔH^o) were negative, which indicates the adsorption process is spontaneous and exothermic. The values of both free energy and ΔG^o indicate that the adsorption is a physical process. This work shows CWS could be utilized as an effective adsorbent for treating dye wastewater.

A simple and effective route to improve the fluorescence of carbon dots is reported. A weak fluorescent solution was obtained by a diminution step to obtain tiny particles from bagasse-based carbonaceous blocks. This solution was subjected to hydrothermal treatment under alkaline conditions to improve its fluorescent performance. The luminescence was found to be improved by more than 20-fold after hydrothermal treatment. The ultraviolet absorption and the surface structure were also significantly changed. The alkaline hydrothermal process was shown to involves hydrolysis, isomerization, dehydration, and polymerization that causes the formation of the C=C double bonds and conjugated structures. The optimum hydrothermal conditions were at 200 °C for 8 h, and the most appropriate ratio of NaOH to the amount of the weak fluorescent solution was 38-40 mg to 1 mL.

In this study, the bleachability of commercial mixed tropical hardwood brown kraft pulp by oxygen delignification (O stage) was examined. It was found that the effective reduction of kappa number was limited to about 35%, and the pulp viscosity was 20.3 cP with a selectivity less than 0.60 and ISO brightness of ca. 43%. The selectivity and pulp brightness of the O stage were improved by adding H2O2 (OP stage) because it decreased the kappa number to a greater extent. However, the addition of hydrogen peroxide caused more serious cellulose degradation. In order to minimize the drop of pulp viscosity during the OP stage, a small amount (0.04%) of anthraquinone (AQ) was added. The results showed that the AQ-aided OP stage was capable of preventing cellulose degradation and thus improved the bleaching selectivity about 60%, in comparison to the ordinary O stage. Moreover, the AQ-OP pulps retained significantly less hexenuronic acid than the pulps from O and OP stages.

Some pulp mills expect to produce viscose fiber by means of pre-existing pulp production lines as used for conventional kraft pulp having a relatively high content of hemicellulose. In the present study oxygen-reinforced alkali extraction was used to dissolve the oxidized lignin, which increased the content of alpha cellulose and increased the degree of mercerization. This paper considers the influence of alkalinity, time, temperature, oxygen pressure, and borax additive on oxygen-reinforced alkali extraction. According to the experimental results, the optimal oxygen-reinforced alkali treatment conditions were 120 g/L alkali for 30 min at a temperature of 40 °C. Single factor experiment results showed that oxygen pressure was beneficial to the process of alkali extraction, and 0.4 Mpa was selected as the optimal oxygen pressure. Kappa number, alpha cellulose, carboxyl content, and degree of polymerization (DP) were 1.2, 99.18%, 0.00965 mmol/g, and 1505, respectively, under the optimal reaction conditions. Results for the oxygen-alkali treatment showed that borax was important for affecting DP and the amount of cellulose II. DP was decreased to 1282 and the amount of cellulose II was increased to 36% when the borax was added.

Urea-formaldehyde (UF) resin (F/U: 1.25), melamine-urea-formaldehyde (MUF) resin (F/(U+M): 1.05), and three kinds of wood species including poplar (Populus davidianaDode), beech (Fagus englerianaSeem.), and eucalyptus (Eucalyptus robusta Smith) were used to produce plywood. The effects of sealing treatment and wood species on the formaldehyde emissions were studied. The anatomical characteristics of different wood species were measured. The results showed that: (1) formaldehyde emission of plywood treated by surface sealing was higher than without treatment; (2) formaldehyde emission of nine-ply poplar plywood bonded by UF resin decreased by 74.4% to 1.98 mg/L after edge sealing treatment; (3) compared with beech and poplar plywood, the formaldehyde emission of five-ply eucalyptus plywood bonded by MUF resin was the lowest obtained, at 0.19 mg/L; (4) formaldehyde emission of poplar plywood from the surface changed slightly in spite of different layers. The contact angle and spreading-penetration coefficient, K, analyses showed that the cell arrangement of eucalyptus was dense. Scanning electron micrographs indicated that the pore sizes of eucalyptus samples were the smallest in contrast to poplar and beech.

Fiberboard is a common interior material used both in China and the United States of America. The increase in demand for interior materials has raised concerns regarding combustibility of the materials. The pyrolysis characteristics of fiber, phenolic resin (PF), and nano kaolin-clay (NK) were investigated using thermogravimetry. The fire performances of samples coated with a mixture of NK and PF were determined using a cone calorimeter. The pyrolysis process of fiber included three phases dependent on chemical composition. The initial temperature of PF pyrolysis was about 100 °C and it stopped at 280°C. The major mass loss of NK was observed between 400 to 600 °C due to the gradual oxolation of the metakaolin. In comparison with fiber board, samples coated with a mixture of NK and PF achieved a better fire performance. The results showed a longer TTI, lower HRR, and THR, and less CO and CO2 yield, especially from a mixture of NK (90%) and PF (10%). The application of an NK and PF mixture to fiber board as a flame retardant is an effective method for enhancing fire safety and resistance.

Nanocrystalline cellulose (NCC) was used as a modifier for waterborne polyurethane (WPU) to investigate the water and ethanol resistance of WPU-NCC composites. The NCC surface was modified with γ-glycidoxypropyltrimethoxysilane (GPTMS) and γ-ammnonimpropylmethyldimethoxysilane (APMDS) to improve its compatibility with waterborne polyurethane (WPU), as indicated by the contact angle (CA). The characteristic properties of WPU modified by NCC and a control group were compared by a Fourier-transform infrared spectroscope (FTIR), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). The CA between the modified NCC and WPU was decreased by 31.2% (with 8.0% APMDS (v/v)), and the NCC modified by GPTMS resulted in a 33.8% decrease of the CA. Compared to the original WPU, the crystal structure and crystallinity of the modified WPU showed a slight alteration. The SEM micrographs showed that the NCC particles modified by GPTMS were dispersed more uniformly. The FT-IR results showed that the addition of modified NCC led to the reduction of the characteristic absorption peak of the hydroxyl group. The water resistance of WPU with 1.5% NCC modified by GPTMS was increased by 47.2%, and the ethanol resistance decreased by 67.0%, while the modification from APMDS led to a 38.1% increase in water resistance and a 56.9% decrease in ethanol resistance.

This paper reports on a novel and efficient β-glucosidase immobilization method using magnetic Fe3O4 nanoparticles as a carrier. Based on response surface methodology, the optimal immobilization conditions obtained were: glutaraldehyde (GA) concentration, 0.20%; enzyme concentration, 50.25 μg/mL; cross-linking time, 2.21 h; and the maximum activity recovery reached 89.35%. The magnetic immobilized enzyme was characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). FTIR revealed that β-glucosidase was successfully immobilized on the magnetic nanoparticles. TEM showed that enzyme-magnetic nanoparticles possessed nano-scale size distribution. VSM confirmed that the enzyme-magnetic nanoparticles were superparamagnetic. The properties of the immobilized β-glucosidase were improved, and the immobilized β-glucosidase exhibited wider pH and temperature ranges of activation, higher accessibility of the substrate, better thermal stability, and better storage stability than that of the free enzyme. The enzyme-magnetic nanoparticles could be separated magnetically for easy reuse. Immobilization of β-glucosidase onto the magnetic nanoparticles has the potential for industrial application.