Research Articles

Acoustic emission (AE) and radial dimensional changes during dehydration under ambient conditions were compared between fully saturated fresh Norway spruce (Picea abies (L.) Karst.) sapwood and sapwood exposed to one or two rewetting-dehydration cycles. The aim of the study was to find out whether AE detected by wideband transducers (100 to 1000 kHz) gives useful information about the mechanical stresses generated during dehydration of small sapwood specimens. AE activity and peak amplitudes became lower after each dehydration-rewetting run. During the first dehydration run the highest peak amplitudes were detected at moderate moisture loss, whereas rewetted wood peaked towards the end of dehydration. AE of fresh, never-dried sapwood was also characterized by a higher count rate of low frequency AE (<175 kHz). Differences in amplitude and frequency clusters between small earlywood and latewood specimens suggest that earlywood is much more sensitive to irreversible processes upon drying than latewood, which might be related to pit functioning and shrinkage anisotropy. At moderate moisture loss, fresh, never-dried sapwood showed higher radial dimensional changes compared to re-wetted sapwood. If it is assumed that fresh, never-dried sapwood is more prone to dehydration stresses than pre-dried sapwood, critical stages during drying can be characterized by high mean peak amplitudes and by a higher count rate of low frequency AE.

This work was designed to provide the Australian structural radiata pine processing industry with some indications for improving stress grading methods and/or technologies to give an increase in structural grade yields, and significantly reduce processing costs without compromising product quality. To achieve this, advanced statistical techniques were used in conjunction with state-of-the-art property measurement systems applied to the same sample of sawn timber. Acoustic vibration analyses were conducted on green and dry boards. Raw data from existing in-line systems was captured on the same boards. The Metriguard HCLT stress rating system was used as the “reference” machine grading because of its current common use in the industry. A WoodEye® optical scanning system and an X-ray LHG scanner were also able to provide relevant information on knots. The data set was analyzed using classical and advanced statistical tools to provide correlations between data sets, and to develop efficient strength and stiffness prediction equations. Reductions in non-structural dry volumes can be achieved.

Moisture sorption in wood-plastic composites (WPCs) affects their durability and dimensional stability. In certain outdoor exposures, the moisture properties of WPCs are altered due to e.g. cracks induced by swelling and shrinkage of the components, as well as UV degradation or biological attack. The aim of this work was to study the effect of different artificial ageing routes on the moisture sorption properties of WPCs. Extruded WPCs were prepared with either unmodified or acetylated wood and recycled high-density polyethylene (HDPE). The WPC samples were artificially aged involving water soaking, artificial weathering, and white- or brown-rot decay in different combinations. After the ageing, the samples were conditioned in either 65% or 90% relative humidity (RH) until equilibrium moisture content was reached. A dynamic moisture sorption analyzer was used to monitor the sorption rate of samples subjected to a climate change from 65% to 90% RH. Scanning electron microscopy was used to study the surface morphology of the aged composites. Results showed that the artificial weathering caused cracking of the HDPE matrix at the composite surface, as well as a wood-matrix debonding, resulting in an increased moisture sorption rate. The WPC samples subjected to white-rot decay showed the highest moisture sorption rate.

Cellulose and hemicellulose account for a large portion of the world’s plant biomass. In nature, these polysaccharides are intertwined, forming complex materials that require multiple enzymes to degrade them. Multi-enzyme complexes (MECs) consist of a number of enzymes working in close proximity and synergistically to degrade complex substrates with higher efficiency than individual enzymes. The aim of this study was to isolate and characterise a (hemi-) cellulolytic MEC from the aerobic bacterium, Bacillus subtilis SJ01, using ultrafiltration followed by size-exclusion chromatography on a Sephacryl S-400 column. Two MECs, C1 and C2 of 371 and 267 kDa, respectively, were purified, consisting of 16 and 18 subunits, respectively, five of which degraded birchwood and oat spelt xylan. The MECs degraded xylan substrates (C1: 0.24 U/mg, C2: 0.14 U/mg birchwood xylan) with higher efficiency than amorphous cellulose substrates (C1: 0.002 U/mg, C2: 0.01 U/mg carboxymethyl cellulose – CMC). Low or no binding to insoluble substrates indicated that the MECs lacked some of the features characteristic of cellulosomes. The significance of this study lies in the discovery of MECs that differ structurally from cellulosomes that can hydrolyse substrates with high hemicellulose content.

One of the most relevant properties of composite materials to be considered is stiffness. Fiberglass has been used traditionally as a fibrous reinforcing element when stiff materials are required. However, natural fibers are been exploited as replacements for synthetic fibers to satisfy environmental concerns. Among the different natural fibers, wood fibers show the combination of relatively high aspect ratio, good specific stiffness and strength, low density, low cost, and less variability than other natural fibers of such those from annual crops. In this work, composites from polypropylene and stone groundwood fibers from softwood were prepared and mechanically characterized under tensile loads. The Young’s moduli of the ensuing composites were analyzed and their micromechanics aspects evaluated. The reinforcing effect of stone groundwood fibers was compared to that of conventional reinforcement such fiberglass. The Halpin-Tsai model with the modification proposed by Tsai-Pagano accounted fairly for the behavior of PP composites reinforced with stone groundwood fibers. It was also demonstrated that the aspect ratio of the reinforcement plays a role in the Young’s modulus of injection molded specimens.

The effect of heat-dispersing on sticky substances in a deinking pulping line was studied under different conditions including varying temperature, disc clearance, and pulp consistency. Sticky substances were quantitatively investigated before and after the heat-dispersing, and categorized into macro-, mini-, and micro-stickies as well as dissolved and colloidal substances. Meanwhile, their extents of removal in post-flotation were evaluated. The results showed that raising temperature, reducing disc clearance, or increasing pulp consistency significantly improved the dispersion of sticky particles, an effect that will be beneficial to their removal in the subsequent flotation process. Under temperature of 100 °C, disc clearance of 0.3 mm, and pulp consistency of 30%, macro- and mini-stickies decreased by 92% and 83%, respectively. Due to being dispersed to smaller sizes, removals of mini- and micro-stickies were enhanced in post-flotation to 25-26% and 68-70%, respectively. Only a small amount of dissolved and colloidal substances was removed in flotation.

In this study, the Young’s modulus and the in-plane shear modulus of 3-, 5-, and, 7-ply Lauan wood (Shorea sp.) were determined by conducting a flexural vibration test with various specimen depth to length ratios and performing a subsequent finite element analysis (FEA). The length and depth directions of the specimen used for the vibration test coincided with the length/width and width/length directions of the plywood panel. The results obtained from the experiment and FEA revealed that the influence of specimen configuration and lamination construction did not significantly affect the measurement of the Young’s modulus. However, the results suggested that the in-plane shear modulus decreased as the depth to length ratio of the specimen decreased. The FEA result suggested that this decreasing tendency is more pronounced as the ply number decreases and the thickness of the plywood increases. A statistical analysis on the experimental results suggested that the length of the specimen must be less than 10 times the depth to reduce the influence of specimen configuration on the measured value of the in-plane shear modulus.

The objective of the study was to investigate physical and mechanical properties of experimental particleboard panels manufactured from oil palm (Elaeis guineensis) biomass without using any adhesives. Different parts of oil palm, including the core and mid sections of trunks, fronds, bark, and leaves, were used to make the panels with an average target density of 0.80g/cm3. Based on the test results, it seems that panels made from bark and leaves did not have satisfactory strength and dimensional stability. However, the panels having particles from the core portion of the trunks exhibited the highest modulus of rupture and internal bond strength but lowest in thickness swelling and water absorption values among the samples. The panels made with particles of mid-section of trunks and fronds followed the samples having core portion trunks material. Three types of raw material, namely fronds, mid-, and core-parts of the trunks appeared as though they could have potential to manufacture particleboard panels with acceptable properties based on requirements stated in Japanese Industrial Standard (JIS). Similar to the above findings, surface quality of the samples were also found acceptable for the panels made from three types of particles. Based on the results of this work, oil palm in the form of biomass could be considered as an environmentally friendly alternative raw material to manufacture binderless particleboard panels.

The biosorption of As(V) from aqueous solutions by pine sawdust chemically modified with iron in batch systems was investigated. The loading process of Fe in this biomaterial was achieved by hydrolysis of two different ferric salts. This modification of sawdust is an attempt to improve As(V) biosorption for practical applications. The kinetics and maximum biosorption capacities of the unmodified and modified pine sawdust were evaluated. It was found that the pseudo-second order model described the As(V) biosorption kinetic data and the Langmuir-Freundlich equation described the arsenate sorption equilibrium. These results indicated that the sorption mechanism was chemisorption on a heterogeneous material. The pH effects governing biosorption capacities were also evaluated, showing a decrease as pH value rises, indicating that this biosorption process is highly pH-dependent. The estimated maximum biosorption capacities of As(V), based on the Langmuir-Freundlich fit to the data were, at pH 4, 4.4 mg/g of untreated sawdust, (UN-SW), 12.85 mg/g of ferric chloride modified sawdust (FeCl-SW), and 6 mg/g of ferric nitrate modified sawdust (FeNit-SW); and at pH 7, 2.6 mg/g of UN-SW, 5.9 mg/g of FeCl-SW, and 4.6 mg/g of FeNit-SW. Sorption capacities of iron-modified pine sawdust were evidently higher than other similar biosorbents previously reported.

This paper provides an applicable approach to identifying flavonoid compounds from bamboo leaves extracts, based on the use of the powerful Liquid Chromatography Electrospray Ionization source in combination with hybrid Ion Trap and high-resolution Time-of-flight Mass Spectrometry (LC-(ESI)-IT-TOF/MS). The strategy involves four procedural steps including searching flavonoid components based on an ultraviolet spectrum scan, getting the accurate mass of flavonoid components parent ion, retrieving the corresponding formula by software, and speculating as to the chemical structure according to mass spectrum decomposition rules. The presently developed methodology has been well proven to be useful and valuable by successful application to the identification of flavonoid components from Dendrocalamopsis oldham leaves. All of the 13 flavonoid components detected have been successfully identified by this approach, except that it failed to confirm 3 flavonoid component chemical structures. The calibration curves of two flavonoid components (orientin and vitexin) that had been identified in bamboo leaves showed a good linear fit (R2≥0.9998) in the concentration range of 6.25 to 200 mg/L. The limits of detection (LOD) were less 0.02 mg/L (S/N=3), and the estimated limits of quantification (LOQ) were less 0.06 mg/L (S/N=10). Intra- and inter-day relative standard deviations were less than 1.04 and 1.82%, respectively.