Research Articles

Principles and methods to dynamically test the Poisson’s ratio of isotropic material and timber are proposed in this work. Five species of lumbers were processed into cantilever plates of tangential, radial, and cross sections with different length-width ratios of 6, 5, 4, and 3. The “Shell 63” element in ANSYS software was adopted to calculate strain and stress under the first-order bending mode. The paste position of the strain rosette for the Poisson’s ratio of timber was obtained through strain-stress relationship and regression analysis under states of stress, strain analysis, and plane stress. This method was also applied to steel, aluminum, and glass. For both isotropic and orthotropic materials such as timber, the paste positions of the strain rosette were determined by the position where transverse stress within the plate was zero during the first-order bending vibration. Meanwhile, the lateral and longitudinal strains of the spectrum were measured using the transient excitation method. In the spectrum, the ratio of linear amplitude between the lateral and longitudinal strain of the first-order bending frequency was taken as the measured value of the Poisson’s ratio of the material. The accuracy of the results was verified by axial tension and static four-point bending tests.

A series of acid hydrolysis lignin-g-poly-(acrylic acid) (AHL-g-PAA) composites was prepared by grafting acid hydrolysis lignin on the surface of the polyacrylic acid network. The results of structure analysis revealed that AHL-g-PAA had been grafted. The surface morphologies of the hydrogels were improved, as shown by scanning electron microscopy observation. The AHL-g-PAA hydrogel had high water absorption and it possessed sensitivity to external pH stimulus. This study also revealed that the adsorption capacity of AHL-g-PAA was 235 mg/g for Pb(II) ions. The adsorption kinetics data could be described by the pseudo-second-order model, and the adsorption isotherm agrees well with the Langmuir model.

The effects of vacuum heat treatment were studied relative to the chemical composition of larch wood. The samples were heat-treated in vacuum at 160 °C, 200 °C, and 240 °C for 4 h, and the chemical changes were investigated by wet chemical analysis, elemental analysis, calorific value determination, and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). The relative percentage contents of lignin and extractives increased after heat treatment. Additionally, the relative percentage contents of holocellulose, cellulose, and hemicelluloses decreased as a result of the thermo-vacuum treatment. Elemental analysis showed a slight reduction in the contents of hydrogen and oxygen. Vacuum heat treatment also increased the calorific value compared with untreated samples.

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.