Volume 54, Issue 4

Changes in dielectric constant and loss factor of two different species of wood namely Sheesham ( Dalbergia Sissoo ) and Bamboo ( Bambusa sp ) are reported in the frequency range 30 Hz–3 MHz following their microbial treatment with Coriolus versicolor . Comparison of dielectric data of C. versicolor treated and untreated wood obtained in oven dried samples and in the samples exposed to atmospheric moisture for more than 2 weeks reflect the alteration in chemical composition of the wood after C. versicolor treatment and its associated altered hydration behaviour. In all the experiments described here the principal feature of the frequency dependent dielectric response is a low frequency dispersion in ∈ ∣ and ∈ ∥ and a weak loss peak observed at a higher frequency. The low frequency dispersion is attributed to localised hopping of charge carriers between neighbouring sites and the higher frequency peak to the reorientation of polar sub molecular species of constituent molecules.

The structure of copper complexes in copper amine treated wood samples were elucidated by the application of electron paramagnetic resonance spectroscopy (EPR). EPR axial spectra were observed for all Cu-amine treated samples irrespective of the formulations. The values of A ∥ and g ∥ of the axial spectra indicate that the stereo-structure of copper complexes in copper amine treated wood was either tetragonal-based octahedral or square-based pyramidal. Comparison of electronic parameters of A ∥ and g ∥ in Cu-amine treated wood with those of the Cu-amine treating solution and the values in literature suggests that the interaction of wood with copper amine is through complexation in which wood functional groups are complexed with copper amine perpendicularly. The copper complexes in both treating solution and treated wood are in the form of CuN2O2, where copper is ligated with 2 nitrogen and 2 oxygen.

Treatment of the water-extracted maize stems with peroxymonosulfuric acid at 20 °C for 144 h, peroxyformic acid at 80°C for 6 h, peracetic acid at 50°C for 6 h, and 2% hydrogen peroxide at 45°C for 12 h at pH 1.5, 4.4, 9.5, 11.5, 12.0, and 12.6, respectively, solubilized 47.1%, 91.3%, 33.3%, 16.6%, 15.9%, 17.4%, 86.2%, 87.7%, and 91.3% of the original lignin, and hydrolysed or dissolved 12.1%, 99.1%, 4.5%, 2.7%, 3.1%, 3.1%, 63.3%, 64.7%, and 83.0% of the original hemicelluloses, respectively. Substantial lignins and hemicelluloses were degraded or released during the treatment with peroxyformic acid and alkaline peroxide at pH ≥ 11.5, while an insignificant effect on delignification and hemicellulose solubilization was observed by using peroxymonosulfuric acid, peracetic acid, and hydrogen peroxide in acidic, natural, and weak alkaline media. The optimum condition for extraction of hemicelluloses was found to use 2% H 2 O 2 at 45°C for 12 h at pH 11.5–12.0, which yielded 63.3–64.7% of the original hemicelluloses having much lighter color than those obtained by peroxymonosulfuric acid and peracetic acid under conditions used and 2% H 2 O 2 at pH 1.5, 4.4, 9.5, and 12.6. Xylose and arabinose were the major sugar constituents in these hemicellulose preparations, whereas glucose, galactose, mannose, rhamnose, and fucose were present as minor components. The α-ether linkages between lignin and hemicelluloses in the cell wall of maize stems were substantially cleaved during the treatment with 2% H 2 O 2 at pH ≥11.5 as shown by a minimal amount of associated lignin (2.9–3.9%), rich in syringyl units, in the solubilized hemicelluloses.

An electron spin resonance (ESR) method combined with a spin trapping technique was applied to trap and characterize unstable radicals which were generated by ultrasonic irradiation of the dimethylsulfoxide (DMSO) solution of a softwood, Yezo Spruce ( Picea jezoensis carr.) lignin. It was found that an unstable secondary carbon radical, ~CH • in the solution was trapped as the stable nitroxide spin adduct when the DMSO solution was subjected to ultrasonic irradiation in the presence of a spin trapping reagent: 2,4,6-tri- tert -butylnitrosobenzene (BNB) at 50°C for 30 min. This means that the alkyl phenyl ether bonds, ~CH-O-phenyl, known as interunitary bonds in lignins were homolytically cleaved by the ultrasonic irradiation, although the phenoxy radical Ph-O •, called guaiacoxy radical, i.e. the counter radical of the secondary carbon radical, was not trapped by the BNB spin trap. This suggests that the trapping of the guaiacoxy radical, having a methoxy group in an ortho -position, by the BNB molecule, carrying two bulky butyl groups in the ortho -positions, is sterically hindered.

Residual lignins of Eucalyptus globulus kraft pulp were shown to be structurally different depending upon the type of extraction chosen. Enzymatic hydrolysis releases a residual lignin with a well preserved etherified structure but substantially contaminated by protein and carbohydrate moieties coming from the enzyme. Moreover, the extraction yield is poor and obviously it does not work as well as in the case of softwood kraft pulp. The residual lignin extracted by acid hydrolysis has less etherified units and more free phenolic functions than that of the enzymatic hydrolysis. It contains some unsaturated structures but no carbohydrate contaminants. Comparison with Milled Wood Lignin (MWL) treated under the acid hydrolysis conditions shows that ether splitting occurs during this extraction. The different residual lignin fractions were characterised by HPSEC, FT-IR, 13 C NMR and sugar analysis.

The molecular weight distribution and functional group contents (phenolic and carbonyl) of lignin samples from the autocatalyzed pulping of Eucalyptus globulus wood were determined. A total of 17 pulping runs were carried out at different conditions according to a surface response design experimental matrix (central composite). The influence of pulping temperature (170–200°C), pulping time (40–120 min) and methanol concentration (30–70%, w/w) on the characteristics of the isolated lignins was studied. Empirical models were developed and used to predict the lignin properties as a function of the cooking conditions. Under high temperature, long cooking time and low alcohol concentration, a rise in functional groups content and a drop in molecular weight of lignin

The behaviour of lignin in wood delignification by oxygen in acidic media in the presence of the molybdovanadophosphate heteropolyanion [PMO 7 V 5 O 40 ] 8− as studied using wet chemistry methods, solid and liquid state 13C NMR spectroscopy. Lignin is oxidised by [PMO 7 V 5 O 40 ] 8− almost completely to carbon dioxide, with a minor yield of intermediate low-molecular weight aromatic products. The analysis of the reaction products shows that the lignin acidolysis and homolysis involving the oxygen participation in oxidation take place. The residual lignin in the wood residue is more “condensed” and richer in guaiacyl structural units than that in the initial wood. The analysis of “condensed” structures issued from permanganate oxidation of residual lignins suggests that these are formed predominantly by acid-catalysed reactions. The use of an organic solvent, such as ethanol, in the pulping solution favours the oxidative delignification, protecting the lignin against competing reactions (condensation).

Kinetics of pine kraft-AQ pulp delignification with the laccase-mediator system (LMS) and the effects of variable factors on the delignification were studied. The delignification was conducted in acetate buffer solution at pH 4.5 and at 40°C under atmospheric pressure. Only a part of the residual lignin could be removed in one-stage processes. Kinetics of kappa number reduction follows a pseudo-second order rate law with pulp consistency of 10 %, mediator charge of 0.1 mmole HOBT/g pulp and laccase charage of 10 U Coriolus laccase/g pulp. Kinetics of dioxygen uptake follows a pseudo-first order rate law up to first 8 hours of the reaction and a pseudo-zero order rate law at the reaction time of 8–24 hours. The amounts of dioxygen consumed per removal of one C 9 -unit equivalent of residual lignin is rather high, 1.5–2.5 mole, and increases with increasing reaction time. Experimental data show that side reactions between the Laccase-Mediator System and products of oxidative degradation of lignin strongly inhibit the delignification either by chemical or physical means or both. Removal of the degraded lignin fragments by alkaline extraction effectively restores the delignification of pulp with LMS. A four-stage process consisting of consecutive treatment of pulp with dioxygen-laccase-HOBT (LMS) followed by alkaline extraction (E), (LMS-E) 4 , decreased kappa number of a pine kraft-AQ pulp from 21.8 to less than 5. On the basis of the kinetic data, the mechanism of the pulp delignification with LMS is discussed.

Ozonations of methylpyranosides, as model compounds for cellulose, were performed in unbuffered aqueous solution at room temperature. The degradation of the pyranosides was followed spectrophotometrically and with high-performance liquid chromatography (HPLC) as a function of ozonation time. The substrates studied were the α- and β-anomers of methyl-D-glucopyranoside, methyl-D-mannopyranoside and methyl-D-xylopyranoside. Methyl-α-D-xylopyranoside degraded more slowly than the other compounds, whereas the rate of degradation was fastest for methyl-β-D-mannopyranoside. In general the degradation of the α-anomers was slower than that of the corresponding β-anomers. HPLC and gas chromatography—mass selective (GC-MS) analyses of the ozonated glucopyranoside samples showed that monosaccharides, lactones, furanosides and acidic compounds are formed during ozonation. A lignin-carbohydrate complex (LCC), containing a D-xylose unit connected to an aromatic part through a βglycosidic bond, was used as a model compound for lignocellulosic pulp. The degradation of this compound during ozonation was also investigated. The results from UV analyses showed that the reaction was extremely fast at the beginning and that the degradation of benzene structures in the lignin mimicking part of the LCC was very rapid. The degradation of the carbohydrate part was slower. This suggests that lignin provides some protection for the cellulose in lignin-containing pulps against attack by ozone. IR and NMR analyses of the freeze-dried ozonated LCC samples showed further that C=O structures are produced during ozonation.

A binuclear [Mn(III)Mn(IV)(μ-O) 2 (μ-CH 3 COO)L](ClO4 − ) 2 complex with L = 1,2 Bis-(4,7-dimethyl-1,4,7-triazacyclonon-1-yl)-ethane, described as a selective catalyst in hydrogen peroxide bleaching of softwood pulps, was tested in hardwood kraft pulp bleaching. The catalyst application gave rise to a higher consumption of peroxide which resulted in higher pulp brightness. The delignification improvement caused by the catalyst was shown to be much lower compared to catalysed peroxide bleaching of softwood kraft pulp. In contrast to the results of softwood pulp bleaching no selectivity improvements could be found when using the catalyst in bleaching of eucalyptus kraft pulp.

The kinetics of delignification of a kraft-AQ southern pine pulp with hydrogen peroxide catalyzed by [LMn(IV)(μ-O) 3 Mn(IV)](ClO 4 ) 2 (1), where L = 1,2-bis(4,7-dimethyl-1,4,7-triazacyclonon-1-yl)ethane was studied. The degree of delignification was significantly improved by using the catalyst. The pulp was bleached for 2 hours at 80°C, in 10% consistency with 2% NaOH, 4% H 2 O 2 and 60 ppm catalyst charges on pulp (O.D.). Kappa number of the pulp was reduced from 31.6 to 16.8 corresponding to a degree of delignification of approximately 4%, while GE brightness was increased from 24.2 to 44.7. At the same time, viscosity of the resulting pulp was reduced from 31.1 mPa•s to 20.1 mPa•s compared to the reduction from 31.1 mPa•s to 20.1 mPa•s in the uncatalyzed bleaching under the same reaction condition. This indicates that the degradation of the carbohydrates was moderate in the catalyzed bleaching compared to the uncatalyzed bleaching. The delignification was found to follow pseudo first order kinetics with respect to kappa number, i.e., residual lignin, in the initial phase and quickly slowed down after 30 minutes (residual phase) under all the reaction temperatures investigated. The delignification rate constants in the initial phase were 0.17, 0.18, and 0.21 min −1 at 50, 60, and 80°C, respectively. Degree of delignification at the delignification time of 30 minutes is approximately 40% at 80°C. The possible delignification mechanism was discussed on the basis of the kinetic studies and lignin model compound experiments.

Shearing is an essential deformation in the treatment of mechanical pulp fibers into a papermaking pulp. Knowledge of the contribution of shear to the fiber treatment during processing can be obtained by measurements on fibers in the form of wood. In this work, an attempt was made to use the Iosipescu method for testing wood in rolling shear. Despite the small size of the shear region of interest between notches made in the wood, the results and their dispersion in both the elastic and inelastic ranges were in accordance with previous results found using other testing methods. The stress-strain relationship was analysed in relation to the specimen's density profiles in the region of interest. Differences in density explained up to 50% of the inter-specimen variability in the shear modulus and in the inelastic behavior. Failure occurred outside the shearing zone in a large number of specimens. Thus the configuration chosen was not adapted to provide for the strength of wood in rolling shear. This behavior limited the amplitude of the strain that could be reached between the notches.

A hypothesis describing tip-crack generation during different machining operations on sapwood of pine surfaces and the differences between the pith side and bark side were investigated. The goal was to determine whether initial tip-cracks are generated already during the machining operation, before weathering. The evaluation of the results showed that about 10 % of the annual rings on the pith side and about 1% of the annual rings on the bark side have cracks after the machining operation. A theoretical analysis of an idealised model using the finite element method (FEM) has also been carried out to investigate the tendency for growth of short initial tip-cracks during a simulation of the compression of a wood piece in a conventional planing operation. The analysis seems to confirm that there is a greater risk for cracks on the pith side than on the bark side.

The microfibril angle of rattan fibers was determined using the iodine staining method and the X-ray diffraction technique. The two were compared to assess the applicability of the X-ray technique in estimating the actual microfibril angle (MFA) of the fiber walls. Likewise, longitudinal Young's modulus and longitudinal shrinkage were evaluated to determine the influence of MFA on the properties of the cane. The X-ray technique gave an accurate and objective estimate of the actual MFA of the fiber walls. A nonlinear relationship existed between MFA and longitudinal Young's modulus while a curvilinear relationship was observed between MFA and longitudinal shrinkage. This pattern is similar to the behavior of wood. Thus, it was deduced that the influence of microfibril angle on the properties of rattan cane is similar to its influence on the properties of wood.

The effects of low molecular weight phenolic resin impregnation and high pressure hot pressing (150°C, 30–100 MPa) on the physical and mechanical properties of wood were first investigated by using sawn wood prepared from a block of Japanese birch ( Betula meximowicziana ). Subsequently, the effects of element size and orientation were examined by using sliced veneers, particles and powder prepared from the remaining portion of the block. Due to the combination of resin impregnation and hot pressing under high pressure, the specific bending strength at 20°C and 65% RH of sawn wood increased 50% accompanied by enormous decreases in moisture content, and bending strength reached around 400 MPa. The mechanical properties of veneer laminated product did not differ significantly from those of sawn wood product. Among isotropic products, the highest bending strength at 20°C and 65% RH of plywood, particleboard and powderboard was 242 MPa, 166 MPa and 175 MPa, respectively. The difference of bending strength between plywood and other isotropic products could be explained by the difference in element orientation, cross lamination and random distribution. Furthermore, the results for the particleboard and powderboard showed that when the resin impregnated elements were hot pressed under high pressure, a decrease in element size did not result in a decrease in bending strength.