Volume 11 Issue 3

α-Glucuronidases are capable of breaking down the α-1,2-glycosidic bonds of 4-O-methyl-D-glucuronic acid residues. As an accessory enzyme, α-glucuronidase plays a vital role in xylan degradation. The recombinant α-glucuronidase from Thermotoga thermarum DSM 5069 was heterologously expressed in the Escherichia coli system, purified, and characterized. The purified enzyme exhibited optimal activity toward aldouronic acids at pH 6.5 and 80 °C. It was fairly thermostable and maintained 98% residual activity after incubation at 65 °C for 2.0 h. The kinetic parameters Km, Vmax, and kcat were 3.02 ± 0.16 mM, 88 ± 2 µmol min-1 mg-1, and 117 s-1, respectively. TtAguA had an apparent activation energy of 59.0 kJ/mol. By structure simulation and mutation analyses, Glu288 was identified as the catalytic proton donor, and Asp367 and Glu395 were likely nucleophile bases. The xylan degradation by endoxylanase Xyn10A was enhanced by approximately 10% in the presence of TtAguA.

Superheated steam (SHS) pretreatment is an effective method for hemicellulose removal from oil palm biomass (OPB) fiber, which leads to the surface modification of the fiber. However, the current SHS pretreatment is conducted at a high temperature and has a long retention time, which causes the removal of cellulose, which is an important component for biocomposite production. This study was conducted to optimize the SHS treatment temperature and retention time so that hemicellulose but not cellulose was removed. Three types of OPB fibers were used: oil palm mesocarp fiber (OPMF), oil palm empty fruit bunch (OPEFB), and oil palm frond (OPF). The chemical composition data was analyzed using a type of response surface methodology (RSM), i.e., central composite design (CCD). The optimal SHS treatment temperature and retention time were 265 °C/5 min, 280 °C/5 min, and 300 °C/9 min for OPMF, OPEFB, and OPF, respectively. The removal of hemicellulose at these temperatures was in the range of 60% to 70%, while the cellulose degradation was maintained below 5%. Statistical analysis showed that the optimal SHS treatment time can be shortened to 5 min to 9 min, which is 18 to 20 times shorter than previously reported methods.

Organosolv wheat straw lignin extracted using the CIMV processTM is a linear, low molecular weight, and natural phenolic oligomer. In this study, organosolv wheat straw lignin was tested as a substitute for 50% to 70% of the phenol in a phenol-formaldehyde-resol resin. The lignin was used without any chemical modification in a one-step synthesis reaction. Parameters such as reaction time and formaldehyde-to-phenol sources (phenol + lignin) mass ratios were optimized to achieve the requirements for industrial wood adhesives in terms of pH, viscosity, and dry matter. For the first time, the formaldehyde ratio was studied in order to reduce resin residual free formaldehyde below 1%. Lignin-phenol-formaldehyde resins were successfully synthesized up to a phenol substitution rate of 70% and showed physico-chemical properties close to standard phenol-formaldehyde resins. The thermo-mechanical properties analyzed in dynamic load thermo mechanical analysis were similar to those of the reference resins. Plywood panels manufactured using these lignin-based resins reached the specifications for industrial panels according to the French standard for exterior plywood panels. Moreover, the formaldehyde content of these plywoods was low enough to satisfy even the most rigorous legislation.

A synthetic method for obtaining a lignin model compound of β-O-4 structure, guaiacyl glycerol-β-guaiacyl ether, was researched through five reaction steps from guaiacol. The key step of this synthetic method was the condensation reaction between 4-(α-bromoacetyl)-guaiacol (III) and guaiacol (I). The compounds were characterized by 1H nuclear magnetic resonance spectroscopy (1H-NMR) and two-dimensional nuclear magnetic resonance (2D-NMR). Pyrolysis behaviors of guaiacyl glycerol-β-guaiacyl ether were investigated by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The thermal behavior and the evolution profiles of major volatile fragments from the guaiacyl glycerol-β-guaiacyl ether pyrolysis were evaluated. Guaiacol is the major product through Cβ-O homolysis at low temperatures. Cβ-O homolysis and Cβ-O concerted decomposition occurred at moderate temperatures, producing guaiacol, 2-hydroxybenzaldehyde, 2-methoxybenzaldehyde, and various phenolic compounds. At high temperatures, the products obtained from Cβ-O homolysis and Cβ-O concerted decomposition experienced secondary thermal cracking, generating a large number of small molecule products, which increased the complexity of the pyrolytic products.

Heating logs prior to peeling positively affects the surface properties of veneer as well as the wood-adhesive bond strength. However, the mechanism behind this increase in strength is not fully understood. The aim of the present study was to separate the influence of soaking temperature and peeling temperature on the physical surface properties and bonding quality. Rotary-cut birch (Betula pendula Roth) logs were soaked at 70 °C, and half of them were subsequently cooled to 20 °C prior to peeling. Surface roughness measurements, scanning electron microscopy (SEM), surface integrity testing, color measurements, and wood-adhesive bond testing were conducted with an automated bonding evaluation system. The results showed that logs soaked at 70 °C and peeled at 20 °C had roughness, color, integrity, bond strength, and wetting properties more similar to logs soaked and peeled at 70 °C than those soaked and peeled at 20 °C. In every test conducted, the effect of soaking temperature was greater than the effect of peeling temperature. High-temperature soaking not only caused softening of the material during the peeling process, but it also caused irreversible changes in the wood material, which affected the veneer surface characteristics and bond strength development.

Selective conversion of biomass-derived carbohydrates into 5-hydroxy-methylfurfural (HMF) is of great significance for biomass conversion. In this study, a novel solid Brønsted acid was prepared simply by the copolymerization of paraformaldehyde and p-toluenesulfonic acid and then used to catalyze the conversion of various carbohydrates into HMF in γ-valerolactone-water (GVL/H2O) reaction medium for the first time. The catalyst exhibited strong acidity, good water resistance, and high thermal stability. The present work focuses on the effects of various reaction parameters, including reaction temperature, time, water concentration, solvent, fructose level, and catalyst loading, on fructose dehydration. The catalyst exhibited excellent catalytic performance for HMF production from fructose in GVL and furnished a high HMF yield of 78.1% at 130 °C in 30 min. The recycling experiments suggested that the solid acid catalyst could be recycled at least seven times without a noticeable decrease in the catalytic activity. In addition, an attempt to study the one-step conversion of sucrose, glucose, and cellulose into HMF and furfural was performed using the same catalytic system.

Selected carbon sources including soluble carboxymethyl cellulose (CMC), insoluble microcrystalline cellulose (MCC), and single (SS)/mixed lignocellulosic substrates (MS), were evaluated for endoglucanase production by B. aerius S5.2. The lignocellulosic substrates of oil palm empty fruit bunch (EFB), oil palm frond (OPF), rice husk (RH), and their mixture (MS) supported growth of the strain better than CMC and MCC. The maximum endoglucanase activity on MS was 7.3-, 2.6-, 1.7-, and 1.2-fold higher than those recorded on MCC, CMC, EFB/OPF, and RH, respectively. While the reducing sugar concentration of the CMC medium was comparable to that of the EFB and MS media, wide variability was observed in the reducing sugar concentrations among the lignocellulosic substrates. Extremely low levels of sugar were detected in the MCC medium, reflecting its poor digestibility and hence unsuitability for growth and endoglucanase production. Endoglucanase production was predominantly extracellular when the strain was grown on CMC and MS. After seven days of fermentation, there was an approximately 25% reduction in MS dry weight. These findings show that the use of mixed lignocellulosics could potentially reduce the cost of cellulase production. Certain novel aspects of the cellulase system of B. aerius are reported in this study.

In spite of the many studies performed, there is not yet a kinetic model to predict the thermal degradation of cellulose in isothermal and non-isothermal conditions for the full extent of conversion. A model proposed by the authors was tested on non-oxidising thermogravimetric data. The method consisted of initially fitting several isothermal and non-isothermal curves, then obtaining a critical temperature and an energy barrier from the set of fittings that resulted from different experimental conditions. While the critical temperature, approximately 226 °C, represented the minimum temperature for the degradation process, the degradation rate at a given temperature was related to both the critical temperature and the energy barrier. These results were compared with those observed in other materials. The quality of fittings obtained was superior to any other reported to date, and the results obtained from each single curve were in line with each other.

Composites containing linear low-density polyethylene/polyvinyl alcohol and various loadings of kenaf fiber were prepared using a Haake internal mixer. The loading of kenaf fiber varied from 10 to 40 parts per hundred resin (phr). The coupling agent 3-(trimethoxysilyl)propyl methacrylate (TMS) was evaluated for its effect on the processing torque, tensile properties, morphology, water resistance, and thermal properties of the composites. Composites without TMS were used as the control. The composites made from TMS-treated kenaf yielded higher stabilization torque, tensile strength, tensile modulus, water resistance, and thermal properties than the control composites. The improvements were attributed to the coupling effect of TMS.

Jute fiber/polyethylene biocomposites were prepared using a hot press molding technique. The effects of maleic anhydride, clay, and silica on the physical, mechanical, and thermal properties of jute fiber-reinforced polyethylene (PE) biocomposites with different fiber loadings (5, 10, 15, and 20 wt.%) were investigated. The biocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The mechanical properties were determined using a universal testing machine. The biocomposite specific surface area, pore volume, and pore size were investigated using the Brunauer-Emmett-Teller (BET) equation. Because of the Si-O-Si stretching vibration, the peak representing the O-H group significantly decreased in the range of 3200 to 3600 cm−1. Jute fiber/PE Maleic anhydride silica composite (JFPEMASC) showed smoother surfaces, which indicated good distribution and better interfacial bonding between the fibers and matrix. The jute fiber/polyethylene/silica composites had a higher surface area and pore volume, with a lower pore size. JFPEMASC was more thermally stable than the other composites, with higher activation energy. JFPEMASC had the highest Young’s modulus among all the biocomposites.