Volume 7 Issue 1

The aim of this study was to investigate the effects of oxygen and moisture content (MC) on the chemical and color changes of black locust (Robinia pseudoacacia) wood during heat treatment. The wood flour was conditioned to different initial MCs and heated for 24 h at a constant temperature of 120ºC in either oxygen or nitrogen atmosphere. The pH values and chromaticity indexes were examined. Diffuse reflectance UV-Vis (DRUV) and Fourier transform infrared (FTIR) spectra were used to characterize the changes of chromophores upon heating. The study demonstrated that the pH values decreased after heat treatment, and it was lower when the heat treated was in oxygen than in nitrogen. The L* decreased significantly, while a* and b* increased. The total color difference ΔE* increased with increasing initial MC until a plateau was reached after 30% MC. The color change was greater in oxygen than in nitrogen. The hydroxyl groups decreased after heat treatment. The releases of acid and formation of quinoid compounds and carboxylic groups during heat treatment were confirmed. Discoloration of wood is due mainly to the condensation and oxidation reactions, which are accelerated by oxygen. Higher MCs are required to obtain the greatest color change of wood in inert atmosphere.

A locally isolated white rot fungal strain Trametes versicolor IBL-04 produced high laccase activities in solid state bio-processing of corn cobs. Addition of glucose and yeast extract (C: N ratio; 25:1) enhanced laccase synthesis. Addition of Tween-80 and CuSO4 enhanced laccase production to 1012 U/mL under optimized process conditions. Laccase was further purified to 2.89-fold (specific activity of 840 U/mg) by ammonium sulfate fractional precipitation, dialysis, and Sephadex G-100 gel filtration chromatography. The purified laccase had a relative molecular mass of 63 kDa as detected by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE). Best enzyme activity was at pH 5 and 40oC. Using 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as substrate, the enzyme showed maximum activity (Vmax) of 780 U/mL with a corresponding Michaelis constant (Km) value of 73µM. Among the different activators/inhibitors, Cu2+, Mn2+, and Fe2+ stimulated laccase activity, whereas EDTA and cystein inhibited the enzyme. The higher Vmax and lower Km for T. versicolor IBL-04laccase as compared to most of the reported laccases suggests its potential for industrial applications.

The extracellular enzyme production capacity of Pleurotus ostreatus MTCC 142 was investigated for decolorization of crystal violet under solid and submerged conditions. Laccases are the major extracellular lignocellulolytic enzymes produced by fungus. Pleurotus ostreatus provided an effective decolorization of dye at 20 mg/L concentration up to 92%. Mycelial growth was observed maximum on plate for a dye concentration 20 mg/L while lowest on 200 mg/L on day 12, respectively. At all concentrations of dye studied, maximum laccase activity was observed on day 8. For 20 mg/L of dye laccase activity was 133 U/L. The decolorization was attributed to microbial action and without role of pH change; less than 0.4 pH change was observed. Manganese dependent peroxidase activity was 106 U/L, maximum on day 8 incubated with 20 mg/L dye concentration. The present study suggested that the high efficiency decolorization of crystal violet by P. ostreatus was assisted by laccase and manganese-dependent peroxidase activity and can be exploited as a promising in biological treatment of waste water containing crystal violet.

The aim of this work was to thermally characterize the renewable lignocellulosic bioresources derived from palm trees in order to highlight their energy potential. Pyrolysis and combustion behaviours of date stones (DS) agricultural by-products were tested by thermo-gravimetric analysis, and the main chemical compositions were analyzed. The work has also been conducted to identify their most important physical characteristics. The study of the sizes and heating rate effects constitute the first part of the experimental work. Inert atmosphere and three heating rates: 10, 20, and 50 °C/min, were applied to various particle sizes of DS. In the second part, tests were carried out in an oxidizing atmosphere (21% O2) by varying the size of the DS. The kinetic parameters such as pre-exponential factor and activation energy were determined. Increasing the particle sizes and the heating rates didn’t have an appreciable influence on the global weight losses. However, degradation rates were significant with the porous structure of the DS. Weight losses in inert and oxidizing atmospheres were found to occur in two stages (drying and devolatilization) and in three stages (drying, devolatilization, and oxidation of the char).

Chemical modification is an often-followed route to improve physical and mechanical properties of solid wood materials. In this study five kinds of tropical light hardwoods species, namely jelutong (Dyera costulata), terbulan(Endospermum diadenum), batai (Paraserianthes moluccana), rubberwood (Hevea brasiliensis), and pulai (Alstonia pneumatophora), were chemically modified with benzene diazonium salt to improve their dimensional stability and water repellent efficiency. The dimensional stability of treated samples in terms of volumetric swelling coefficient (S) and anti-swelling-efficiency (ASE) were found to improve with treatment. The water repellent efficiency (WRE) values also seemed to improve considerably with treatment of wood samples. Furthermore, treated wood samples had lower water and moisture absorption compared to that of untreated ones.

The mechanical properties and structure of cactus Opuntia ficus-indica spines were characterised in bending and by means of x-ray diffraction. Using spruce wood cell walls for reference, the modulus of elasticity of Opuntia cactus spines was high in absolute terms, but comparable when specific values were considered, which can be explained by similarities in the cell wall structure of both materials. Differently from the modulus of elasticity, the bending strength of cactus spines was unexpectedly high both in absolute and in specific terms. The unique cellulose-arabinan composite structure of cactus spines, together with high cellulose crystallinity, may explain this finding.

The easy leaching of boron from wood preservation formulations has limited the use of this highly active fungicide. The recently discovered adduct with flavonoids allows boron to be retained for longer periods of time within wood and consequently to extend its life. Two different leaching treatments were compared, and the fungal and termite decay were examined. The biological tests showed extremely high resistance of the leached samples against both fungus (Coriolus Versicolor and Coniophora Puteana) and termites (Reticulitermes Santonensis). The retention of 2.5 kg/m³ was determined as the threshold of efficacy of boron in flavonoid-based wood preservative. Furthermore, solid state 13C-NMR analysis of the tannin resin indicated that boron can be covalently fixed to the tannin-hexamine network.

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.