Research Articles

In this study, glyoxalated alkaline lignins with a non-volatile and non-toxic aldehyde, which can be obtained from several natural resources, namely glyoxal, were prepared and characterized for its use in wood adhesives. The preparation method consisted of the reaction of lignin with glyoxal under an alkaline medium. The influence of reaction conditions such as the molar ratio of sodium hydroxide-to-lignin and reaction time were studied relative to the properties of the prepared adducts. The analytical techniques used were FTIR and 1H-NMR spectroscopies, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Results from both the FTIR and 1H-NMR spectroscopies showed that the amount of introduced aliphatic hydroxyl groups onto the lignin molecule increased with increasing reaction time and reached a maximum value at 10 h, and after they began to decrease. The molecular weights remained unchanged until 10 h of reaction time, and then started to increase, possibly due to the repolymerization reactions. DSC analysis showed that the glass transition temperature (Tg) decreased with the introduction of glyoxal onto the lignin molecule due to the increase in free volume of the lignin molecules. TGA analysis showed that the thermal stability of glyoxalated lignin is not influenced and remained suitable for wood adhesives. Compared to the original lignin, the improved lignin is reactive and a suitable raw material for adhesive formulation.

Oil palm ash (OPA), a bio-agricultural waste from oil palm mills, was subjected to high-energy ball milling for 30 h and was converted into a nano-structured material. The nano-structured OPA was characterized for its particle size and crystallinity index by using Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD) analysis. The crystallite size obtained from TEM and XRD was found to be 50 nm and 54.32 nm respectively, and the crystallinity index of OPA was 66.54%. The shape and texture of raw and nano-structured OPA were studied using scanning electron microscopy. The raw OPA had an irregular shape with spongy and porous structure, while the nano-structured powder had a mostly irregular and crushed shape. The elemental studies of OPA used Energy Dispersive X-ray (EDX) analysis, XRD, and Fourier Transform Infrared Spectroscopy (FT-IR). The elemental compositions found in OPA were silica, potassium oxide, calcium oxide, magnesium oxide, aluminium oxide, and iron oxide.

Non-isothermal crystallization of neat high density polyethylene (HDPE), wood flour (WF)/HDPE composite (WPC), virgin Kevlar fiber (KF) reinforced WPC (KFWPC), and grafted Kevlar fiber (GKF) reinforced WPC (GKFWPC) was investigated by means of differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). Several theoretical models were applied to describe the process of non-isothermal crystallization. The results showed that the Avrami analysis modified by Jeziorny and a method developed by Mo and coworkers successfully described the non-isothermal crystallization behavior of HDPE and composites. The Ozawa analysis, however, failed to provide an adequate description of non-isothermal crystallization. The values of crystallization peak temperature (Tp), half-time of crystallization (t1/2), and kinetic parameters KJ and F(T) showed that the crystallizability followed the order: FKWPC > GKFWPC > HDPE > WPC. The effective activation energy for non-isothermal crystallization of HDPE and composites based on both Kissinger and Friedmen methods was evaluated. WAXD indicated that the crystalline thickness perpendicular to the reflection plane (Lhkl) increased with the addition of KF. The results demonstrated that KF and GKF can act as nucleating agents and increase the crystallization rate of HDPE. Compared with GKF, KF is a more effective nucleating agent for HDPE, and wood flour cannot act as a nucleating agent for HDPE. PDF

Lignin recovered from the near-neutral hemicellulose extraction process was investigated as a precursor suitable for production of carbon fiber. Crude lignin was precipitated from the wood extract by adding sulfuric acid to lower the pH value to 1.0. The crude lignin extract was then upgraded by using hydrolysis to cleave lignin-carbohydrate bonds and to remove carbohydrates that contaminate the lignin. The precipitated solids were separated by filtration, washed with water, and then dried. Lignin recovered using the hydrolysis method was found to be high in carbon, high in total lignin, low in inorganic contamination, and low in insoluble material, but high in volatile material. The recovered lignin could be thermally spun into lignin fibers, but the spun fibers proved to be brittle, which was thought to be due to its low-molecular mass and the glassy nature of lignin. Micrographs obtained using scanning electron microscopy (SEM) illustrated imperfections on the surface and in the interior microstructure of the carbon fiber when compared to micrographs taken of commercial carbon fiber manufactured using PAN and pitch. These imperfections were thought to be related to the high volatile material content in the samples and the slow rate of heating during the carbonization process. Baker (2011) suggests that increasing the rate of heating during carbonization can reduce the degree of brittleness and improve mechanical properties.

This study was performed to determine the effects of thermal aging on the film hardness of some wood varnishes. For this purpose, Scots pine (Pinus sylvestris L.), Eastern beech (Fagus orientalis L.), and oak (Quercus petraea L.) samples coated with synthetic (alkyd), two-part polyurethane (urethane-alkyd), and waterborne (self cross-linked polyurethane) varnishes were evaluated at a moisture content of 8% and 12%. Afterwards, thermal aging processes were performed for periods of 25, 50, 75, and 100 days at 25 ºC, 50 ºC, 75 ºC, and 100 ºC. Hardness changes in the varnish films were measured in accordance with ISO 1522-2006. According to the test results, the samples prepared with polyurethane varnishes at 8% moisture content give the best results.

In a biorefinery context it is an advantage to fractionate and extract different wood components in a relatively pure form. However, one major obstacle for efficient extraction of wood polymers (lignin, polysaccharides etc.) is the covalent lignin-polysaccharide networks present in lignified cell walls. Enzymatic catalysis might be a useful tool for a controlled degradation of these networks, thereby enhancing the extraction of high molecular weight polymers. In this work, a methanol-alkali mixture was used to extract two different wood samples treated with endoxylanase and gammanase, respectively. Wood chips were pretreated with alkali prior to enzymatic treatment to enhance the cell-wall accessibility to enzymes. Extractions were also carried out on non-enzyme-treated samples to evaluate the enzymatic effects. Results showed that the enzymatic treatment increased the extraction yield, with gammanase as the more efficient of the two enzymes. Furthermore, polymers extracted from xylanase-treated wood had a higher degree of polymerization than the reference.

In this study the effect of processing parameters on different types of wood raw material in extrusion was examined. The study consisted of two parts: the first part was to break and separate individual fibers from wood chips during the extrusion process; in the second part the effect of chemical pre-treatment and screw elements on wood raw material was evaluated. Statistical analysis was performed to evaluate the most important factors affecting wood particle size in extrusion. The statistical analysis showed that the screw speed is the main factor affecting wood fiber length in twin-screw extrusion of wood chips. This study showed that a twin-screw extruder can be used to separate individual fibers from wood chips, and the separated fibers have higher aspect ratios than the wood flour particles typically used in wood-polymer composites. When more fibrous and chemically softened wood raw material was used, fibers with even higher aspect ratios were obtained.

Iran is facing a severe lack of fibrous raw materials for paper production. Kenaf (Hibiscus cannubinus L.) is a superior complement to wood as a source of fiber. Kenaf bast fibers are excellent for making pulp and paper of various grades due to the presence of high alpha cellulose (56.43), holocellulose (77.71), and ultimate fiber length (2.77 mm). Fiber length is an important factor in the development of tear and tensile properties. The aim of this work is to study the effect of charge alkali (20 and 25% oven dried, as NaOH) and cooking time (30, 60, 90, 120, 150, and 180 min) of kenaf bast fiber on soda and soda-anthraquinone (AQ) pulp yield, kappa number, rejects, and strength properties of their handsheets. Results indicated that alkali charge and cooking time had significant influence on kappa number, yield, and rejects of pulps, whereas PFI revolution had only a minimal effect, especially at higher cooking times. The soda method was modified by adding 0.2% anthraquinone, and the resultant pulps displayed an increase in pulp yield and reduction in both kappa number (by 6 to 9 units) and screening rejects. The strength properties obtained with the two cooking processes used were compared, and those provided by soda-AQ process were found to be best. Regarding handsheet properties, a significant improvement in tensile index could be obtained by the soda-AQ process, compared to the soda process.

Cellulose/chitosan homogeneous solutions were prepared in 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac) ionic liquid. Steady and oscillatory dynamic rheological properties were studied with a Haake Mars-ΙΙΙ rotational rheometer. Rheological results show that cellulose/chitosan [EMIM]Ac solutions are a pseudoplastic liquid, and the viscosity of the solution decreases with increasing of chitosan content. The zero shear rate viscous activation energy of solution is about 52.10 to 62.50KJ/mol, calculated from the Cross and Arrhenius equation. The structural viscosity index of the solution is similar to that of cellulose/N-methylmorpholine-N-oxide solution, which indicates a potential spinnability. The dynamic rheological responses reveal that the Cox-Merz rule holds well with the solutions, and the crossover point of loss modulus and storage modulus shifts to a higher frequency range with increasing temperature.

A study was conducted to quantify tar formation in a stratified downdraft gasifier using wood pellets. The effect of biomass flow rate on tar concentration was also analyzed, and more than thirty compounds in tar were quantified. Among the different compounds in tar, tertiary condensed products such as toluene, o/p-xylene, naphthalene, phenol, styrene, and indene were observed in significant amounts. Tar concentration in the syngas was found to be in the range of 340 to 680 mg/Nm3. These concentrations were found to be much higher when compared to a similar gasifier using woodchips.