Research Articles

Longitudinal compression can help wood form some folds on the wood cell walls after a suitable softening procedure. These folds can enhance the one- and multi-dimensional bending performances of wood. The longitudinal compression properties of alkali-treated juvenile and mature northeast Chinese ash (Fraxinus mandshurica Rupr.) were analyzed. Elastic and elastic-plastic stages were inferred from the longitudinal compression curves. Scanning electron microscopy images showed that some folds formed in the wood cell wall vessels and fibers. X-ray microdensitometer test results showed a decrease in the fluctuation of the wood cell wall density of the specimens. The swelling and degradation or extraction of hemicellulose, lignin, and extractive occurred after alkaline treatment. Slippage between cellulose chains and curving within a cellulose chain were inferred during longitudinal compression. Juvenile wood specimens had higher modulus of elasticity and larger variability than mature wood after alkaline treatment. This finding can be attributed to the higher extent of degradation or extraction of hemicelluloses, lignin, and extractive, as well as the smaller microfibril angle and the similar cellulose crystallinity of treated juvenile wood compared to those of mature wood specimens after alkaline treatment.

Lignocellulosic biomass is a relatively inexpensive and abundant feedstock for biofuel production. The key to unlocking the recalcitrance of lignocelluloses is an effective pretreatment process. A promising new pretreatment method for lignocellulosic biomass is the use of ionic liquids (ILs). In this study, wood flour was partially dissolved in the novel ionic liquid 1-butyl-3-methylimidazolium acesulfamate ([BMIM]Ace) mixed with different organic solvents (1,4-dioxane, acetone, methanol, DMSO, and DMF) followed by precipitation in water. Hemicelluloses were successfully extracted from the carbohydrate-enriched residues by an alkaline ethanol solvent. Sugar analysis of the hemicellulosic fractions indicated that xylose (63.25-74.85%) was the major sugar component, while small amounts of glucose (4.85-14.40%) and galactose (4.49-7.32%) were also observed. Molecular weights of these fractions varied between 49.330 and 60.760 g/mol as determined by GPC. NMR studies revealed that the hemicelluloses had a backbone of β-(1→4)-linked-D-xylopyranosyl units and were branched mainly through 4-O-methyl-α-D-glucuronic acid. The thermal degradation behavior of the hemicellulosic fractions showed that the most significant degradation occurred between 242 and 300 °C.

Two pretreatment methods, microwave irradiation and steam explosion, were investigated in this work. The aim of the study was to investigate whether these methods would improve the biodegradability of wheat straw as a lignocellulosic feedstock. Microwave pretreatment was carried out on milled straw with an irradiation time of 15 minutes, at a temperature of either 200 or 300 °C in the oven. The steam explosion pretreatment was carried out on milled straw at 210 °C for 10 minutes. To determine the methane production potential, anaerobic digestion batch trials were run under mesophilic conditions for 60 days. The methane yields of the microwave-pretreated straw decreased by 65% for an attained temperature of 200 °C and by 92% for 300 °C. After steam explosion pretreatment, however, the methane yields of the straw increased by approximately 20% when compared to untreated straw samples. These results indicate that microwaving does not optimize methane production from wheat straw, while steam explosion yields positive results.

Reed (Phragmites australis) is a natural biological material that has great potential as reinforcing material in bio-composites. In order to evaluate the potential of reed stalk for reinforcement, the microstructure, elemental composition, microfibril angle (MFA), and mechanical properties of fiber cell walls were investigated by means of scanning probe microscopy (SPM), energy dispersive analysis of X-rays (EDAX), X-ray diffraction (XRD), and nanoindentation, respectively. The effects of elemental composition and microfibril angle of reed fibers on the mechanical properties were also considered. The results indicated that reed fiber cells have a multilayered structure. The observed increase in lignin content and decrease in MFA may contribute to the increase of mechanical properties. The elastic modulus and hardness of fibers in the upper part of the reed stalk were higher than those of the lower part. Based on nanoindentation results found in the literature, reed fibers have higher elastic modulus and hardness than poplar and spruce fibers.

Water-based finishes are slowly replacing solvent-based finishes in the wood industry. Wood grain raising is an important issue associated with the use of water-based stains. In this paper, water-based and solvent-based stains were applied on yellow birch veneers and hardwood samples that had been previously sanded. Grain raising phenomena were studied by profilometry and microscopy. This study demonstrated that the appearance of wood surfaces treated with water-based and solvent-based stains is affected by a number of factors, including grain raising, surface preparation quality, and substrate type. Main observations are: 1) the sanding method has an important role in the grain raising generation and finish quality; 2) profilometry experiments revealed that developed interfacial area parameter can provide valuable information, as it captures both grain roughness and small-scale roughness due to raised fiber fragments; 3) differences between sawn lumber and peeled veneer appeared minor, although the lumber exhibited less significant differences between water-based and solvent-based finishing systems; and 4) wood fragments on the wood surface would be difficult to eliminate.

Kenaf (Hibiscus cannabinus L.) is a renewable carbon-rich lignocellulosic resource for fermentable sugars. In this study, kenaf cores cultivar V36 from four-month-old stems were pretreated by i) physical, ii) physical and thermal, and iii) physical and chemical methods. The celluloses of pretreated kenaf core particles were then hydrolyzed into fermentable sugars by cellulase from Trichoderma reesei (C2730). The pretreated kenaf core particles were incubated for 48 h at 37 °C. The efficiency of bioconversion was mainly dependent on the pretreatments applied prior to the hydrolysis process. The effects of the pretreatments on kenaf core’s lignin, holocellulose, and cellulose contents were also determined. Kenaf cores without pretreatment had 19.4% lignin, 86.2% holocellulose, and 47.4% alpha-cellulose. The combination of physical and chemical pretreatment on kenaf cores cultivar V36 resulted in a higher cellulose content (92.49%) and produced 50 times higher sugar concentration than the physical pretreatment.

This study aims to optimize the medium for xylanase activity by a newly isolated strain of Rhizopus stoloniferJS-1008 (R. stolonifer JS-1008) under solid-state fermentation (SSF) on corncob. Four quantitative variables impacting the enzyme activity were selected through one-factor-at-a-time design. They were nitrogen source, initial moisture content (IMC), inorganic salt, and surface active agent. In addition, the interaction among these factors was further investigated by response surface methodology (RSM). Statistical analysis revealed that among these factors, IMC and urea significantly affected the xylanase activity. Our data indicate that the optimal medium contains (g/g dry corncob): urea, 0.15; ZnSO4, 0.022; Tween-80, 0.08; IMC, 3. Under the optimal condition, the xylanase activity reached its maximum, 13.90 U/g dry substrate (DS), on the 10th day of fermentation. This work provides a new potential strain to synthesize xylanase for biofuel production.

The main goal of this research was to establish the energy balance from the drying of oil palm empty fruit bunches (EFB), pineapple plant leaves (PL), and sawdust from Gmelina arborea (GAD). Three drying techniques (air, solar, and hot air drying) were tested. The initial moisture content (MCi), drying time, moisture content (MC) variation with time, transformation energy, transportation and drying energy, drying critical point, and the energy balance were measured. MCi was higher for PL (over 79%), followed by EFB (over 47%), and GAD (under 47%). Drying time varied from 27 to 342 hours depending on the technique used. PL presented the longest drying time, followed by GAD, and finally EFB. The transformation energy input was only applied to PL, and the values ranged from 0.041 to 0.09 kWh/kg. Energy used for transportation ranged from 0.051 to 0.090 kWh/kg. Energy consumption ranged from 0.20 to 1.90 kWh/kg, and its mathematical model regarding MC was β1MC3+β2MC2+β3MC+β4 (polynomial) or β1ln (MC) +β2 (logarithmic). A critical value of MC was found, where an inflection of energy consumption occurs during the drying process for all residues. The critical MC for GAD was 10%. For EFB it varied from 11 to 13%. For PL it varied from 4% to 13%. The best energy balance was obtained for GAD and EFB (4.0 to 4.5 kWh/kg) when MC was less than 10%. The best energy balance for PL was obtained when MC varied from 30 to 40%.

Aqueous fractionation of wood has been proposed as a suitable processing method for biorefineries. When treatments are performed under low severity conditions, water-soluble components (which could be detrimental in further processing stages) are removed, whereas polysaccharides, lignin, and other water-insoluble constituents remain in solid phase with little alteration. In order to explore the presence of added-value products in aqueous extracts from Pinus pinaster wood, different samples (heartwood and sapwood with and without knots) were extracted with water at 130 to 140 ºC, and the resulting solutions were assayed for yield and composition (by GC-FID, GC-MS, and HPLC). The major extract components, such as polysaccharide-derived products, simple phenolics, stilbenes, lignans, flavonoids, organic acids, jubaviones, steryl esters, and triglycerides, were identified and quantified. In order to assess a possible application of the extracts, their antioxidant activity was measured using the Trolox Equivalent Antioxidant Capacity assay.

Stress relaxation has been proven to be a good measure for studying the interaction between the constituents in wood flour/polymer composites by evaluating the internal bonding quantitatively. In order to investigate the combination effect of polyethylene glycol (PEG) impregnation and heat treatment on the interfacial compatibility of wood flour/polypropylene composites, the stress relaxation of PEG and/or thermally modified wood flour/polypropylene composites was determined at three temperatures (26, 40, and 60 °C). The apparent activation energy (DE) was also calculated according to Eyring’s absolute rate reaction theory. The results showed that PEG treatment accelerated the stress relaxation rate of the composites and decreased the DE. However, heat treatment resulted in an alleviation of the increasing rate of stress relaxation caused by PEG modification and an increase in the DE of the composites. These results suggested that PEG treatment had a negative effect on the interfacial compatibility between wood flour and polypropylene in the composites, and heat treatment could compensate for this effect to a certain extent.