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August 1, 2006
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August 16, 2006
Abstract
Based on previous investigations on the substitution pattern of stabilized and fresh viscose, different viscoses were analyzed by gel permeation chromatography (GPC) with multiple-angle laser light scattering, refractive index (RI), and UV detection. Viscoses derivatized with N -methyl-N-phenyl-iodoacetanilide are stable over a long time and largely improve handling for analytical purposes. In addition, the derivatized xanthogenate groups exhibit UV absorbance that can be used to detect their distribution along the polymer molecule, once the polymer is dissolved. UV assay indicated that in technical viscoses the distribution of substituents is uniform. Enzymatic degradation with endoglucanases was followed by analysis of the degradation pattern by GPC. Even though the degree of substitution (DS) of xanthogenate groups ranged from γ=0.4 to 0.6, endoglucanases were able to slightly degrade the viscose. Ultrasonic degradation resulted in a narrow molecular weight distribution (MWD), notably without cleavage of substituents, and was also used to improve the solubility of the stabilized viscoses for further analysis. The techniques applied provide more insight into the xanthogenate distribution along the MWD. Remarkable differences in the degradation behavior of both viscose samples were observed.
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August 16, 2006
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Single tension-wood fibres from poplar were investigated using a synchrotron radiation X-ray microbeam. The resulting diffraction patterns are highly resolved (smallest d -spacing 0.11 nm). In the gelatinous layer, cellulose microfibrils of high perfection are found in almost ideal parallel alignment. Their cross-section is approximately four-fold greater than that of microfibrils in the S2 layer of the same wood cell. The results are discussed in terms of the influence of encrusting cell wall polymers and cellulose biosynthesis on the structure of wood cellulose microfibrils. In temperature-dependent experiments, the low-temperature thermal expansion coefficients of crystalline cellulose were determined.
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August 16, 2006
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The crystalline structure of chitin and chitosan was investigated by X-ray diffraction (XRD). Chitosan filaments were prepared using a saturated solution of calcium chloride dihydrate in methanol (CaCl 2 -MeOH) as a mild solvent and the study focused on the interaction between the degree of acetylation (DA) and crystallinity. There were pronounced differences in the XRD patterns for specimens with DA values between 44.2% and 52.2%. We suggest that the crystalline structure changes from an anhydrous-type chitosan to an α-chitin type without any additives. CaCl 2 -MeOH is a good solvent for chitin and a poor solvent for chitosan and we found that it can regulate the distribution of N -acetyl glucosamine and glucosamine between amorphous and crystalline regions.
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August 16, 2006
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Several mutants of chitinase A1 from Bacillus circulans WL-12 have been prepared by site-directed mutagenesis of tryptophan 433. The hydrolytic activity of these mutants toward p -nitrophenyl chitobioside was lower than that of wild-type chitinase A1. The mutants were found to catalyze the transglycosylation reaction of the 1,2-oxazoline derivative of N -acetyllactosamine (Gal-GlcNAc-oxa) to N,N′ ′-diacetylchitobiose (GlcNAc-GlcNAc), giving rise to a transglycosylated tetrasaccharide product (Gal-GlcNAc-GlcNAc-GlcNAc) in high yield. Based on these results, a one-pot synthesis of chitooligosaccharides by combined use of mutant W433Y and β-galactosidase has been demonstrated. By controlling the reaction conditions, chitotriose and chitotetraose were obtained in 74% and 40% yield (determined by HPLC), respectively, without isolating any intermediate products.
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August 16, 2006
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The first total synthesis of plantamajoside ( 1 ), 2-(3′,4′-dihydroxylphenyl)ethyl-4- O -caffeoyl-3- O -(β-D-glucopyranosyl)-β-D-glucopyranoside, which is one of the dihydroxyphenylethyl glycosides (caffeic acid sugar esters), is described. Key intermediate 2 , 2-[3′,4′-bis( O -benzyl)phenyl]ethyl 2,6-di- O -acetyl-4- O -[3′,4′-bis( O -benzyl)caffeoyl]-β-D-glucopyranoside was glycosylated with trichloroacetoimidoyl 2,3,4,6-tetra- O -acetyl-α-D-glycopyranoside ( 3 ) to afford plantamajoside derivative 4a , 2-[3′,4′-bis( O -benzyl)phenyl]ethyl 2,6-di- O -acetyl-4- O -[3′,4′-bis( O -benzyl)caffeoyl]-3- O -(2,3,4,6-tetra- O -acetyl-β-D-glucopyranosyl)-β-D-glucopyranoside, in 39% yield. Plantamajoside derivative 4a was successfully converted into the target compound, plantamajoside ( 1 ), through a series of de-protective procedures. 1 H- and 13 C nuclear magnetic resonance (NMR) spectral data of the synthesized plantamajoside ( 1 ) were identical to those of the natural compound.
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August 16, 2006
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Sulfide diffusion into wood has a rapid reversible component and a much slower irreversible component. During the initial reversible phase, sulfide is unable to diffuse into parts of the wood structure, probably because of charge exclusion. The diffusion of hydroxide and sulfide into saturated wood was imaged by immersing chips in white liquor, splitting them open and then imaging the hydroxide and sulfide profiles. Sulfide moves into the interior of the chip at a faster rate than hydroxide does because it is prevented from entering some of the pores and must move deeper into the chip to access dilution water.
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August 16, 2006
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Modified wood fibres open new perspectives to create value-added products based on renewable raw materials. An interesting option is the targeted modification of fibre surfaces by oxidative enzymes. This two-stage functionalisation method consists of enzymatic activation of fibre surfaces followed by addition of radicalised compounds reacting preferentially by radical coupling. In this work, the activation of bleached and unbleached softwood TMPs with laccase isolated from Trametes hirsuta was studied. The formation and stability of the radicals were studied by EPR spectroscopy. The reaction of the radicals with 3-hydroxytyramine hydrochloride and the type of chemical linkages were investigated. EPR, ESCA and FTIR spectroscopy were used for analysis. Bleached TMP was radicalised more efficiently than unbleached TMP. The radicals were unstable, as 90% of them were quenched within a few hours. Their lifetime was, however, found to be adequately long for performing coupling reactions. Bonding of new compounds to pulps via radical reactions thus seems to be possible.
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August 16, 2006
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The liquefaction of wood ( Metasequoia glyptostroboides ) has been studied in two imidazole-based ionic liquids: IL1, 3,3′-ethane-1,2-diylbis(1-methyl-1 H -imidazol-3-ium) dichloride; and IL2, 3,3′-ethane-1,2-diylbis(1-methyl-1 H -imidazol-3-ium) dichloroaluminate. Rapid and complete liquefaction was obtained in IL2 without residue at 120°C for 25 min, in contrast to liquefaction in phenol/H 2 SO 4 (liquid/wood ratio 20:1) with 25.9% residue. Temperature- and time-dependent studies indicate that the performance of the reagents investigated is IL2>IL1> phenol/H 2 SO 4 . The liquid/wood ratio and the amount of AlCl 3 as catalyst affect the liquefaction rate. In the course of liquefaction with IL2, AlCl 3 plays a dual role as a catalyst and a liquefaction reagent. Ionic liquids separated from the liquefied product can be recycled at least five times to maintain a good liquefaction rate.
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August 16, 2006
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Dehydrogenative polymerization of isoconiferin (IC; coniferyl alcohol γ- O -β-D-glucopyranoside) catalyzed by horseradish peroxidase (HRP) was carried out. The polymerization of IC proceeded in a homogeneous system, resulting in a water-soluble dehydrogenation polymer (IC-DHP). The degree of polymerization (DP) of IC-DHP was significantly higher than that of a standard dehydrogenative polymer (CA-DHP) obtained from coniferyl alcohol (CA) in a heterogeneous system. Under optimum conditions, the DP of IC-DHP was 44 ( M n =1.5×10 4 ), whereas that for CA-DHP was only 11 ( M n =3.0×10 3 , as acetate). Spectroscopic analyses confirmed that IC-DHP has a lignin-like structure containing D-glucose moieties attached to the lignin side-chains. The D-glucose unit introduced into γ-O position of CA essentially influenced the water solubility and molecular mass of the resulting DHP.
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August 16, 2006
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Three new phenolic compounds (4-hydroxy-2-methoxyphenyl-6- O -syringoyl-β-D-glucopyranoside, 2-hydroxy-4-methoxyphenyl-6- O -syringoyl-β-D-glucopyranoside, and 4-hydroxymethyl-2-methoxyphenyl-6- O -syringoyl-β-D-glucopyranoside) and 15 known phenolic compounds (two phenyl glucoside esters, five lignans, three diarylheptanoids and five simple aldehydes or ketones) were isolated from the secondary xylem of mature Betula pendula Roth. The compounds were identified on the basis of their NMR (1D and 2D) and mass spectral data. In total, 23 phenolic extractives present in the sapwood of two winter-dormant B. pendula trees felled at different growing sites (rich in nutrients and scarce in nutrients) were quantified by GC. Their amounts were mostly low, 0.01–0.18 mg g −1 of dry wood. Total amounts of the phenolic extractives isolated were 1.2 mg g −1 of dry wood (5.6% of the total methanol-soluble extractives) in the tree felled at the site rich in nutrients, and 1.9 mg g –1 of dry wood (10% of the total methanol-soluble extractives) in the tree felled at the site scarce in nutrients.
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August 16, 2006
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Odor is one of the most distinctive characteristics of wood. Woods in the family Taxodiaceae and Cupressaceae often emit fragrant odors. In this study, the fragrance compounds of six coniferous woods grown in Taiwan, namely Chamaecyparis formosensis , Chamaecyparis obtusa var. formosana , Calocedrus macrolepis var. formosana , Taiwania cryptomerioides , Cunninghamia lanceolata , and Cryptomeria japonica , were studied by solid-phase microextraction and GC/MS. A non-biased overall profile of the fragrance compositions of the woods was obtained. The major aroma compounds were: β-elemene (15.8%), γ-cadinene (12.1%), α-pinene (11.1%), and limonene (10.8%) in C. obtusa ; myrtenol (27.0%), myrtenyl (19.2%), and γ-cadinene (11.4%) in C. formosensis ; β-cedrene (22.3%), δ-cadinene (17.6%), and widdrene (11.4%) in T. cryptomerioides ; β-cedrene (26.2%) α-pinene (19.7%) and limonene (13.2%) in C. lanceolata ; 3-carene (21.0%), p -cymene (11.0%), and limonene (9.5%) in C. japonica ; and p -cymene (24.4%), terpinen-4-ol (16.6%), and α-terpineol (12.5%) in C. macrolepis . The results may provide useful information for future studies on chemotaxonomy and metabolomics of conifers.
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August 16, 2006
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Oriented strand board (OSB) made of Scots pine ( Pinus sylvestris L.) releases high amounts of terpenes and aldehydes. These volatile organic compound (VOC) emissions are clearly affected by the manufacturing parameters. As a consequence of high temperatures during hot pressing, terpene emissions from OSB are reduced. Aldehyde emissions are initially lowered after pressing at a high temperature (260°C). Furthermore, emissions are influenced by the surface structure. If the surface consists of fine particles, terpene emissions are lowered and the course of aldehyde formation is altered. Nevertheless, a reduction in VOC emissions by adjustment of the parameters investigated in this work seems to be restricted to terpenes. Aldehyde emissions from all panels converge during emission testing and in the final stages no clear distinction is possible according to the pressing temperature or surface structure.
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August 16, 2006
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August 16, 2006
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In this research, square-plate twist test methods for obtaining the shear modulus of wood were examined. Square plates of western hemlock ( Tsuga heterophylla Sarg.) were used as specimens. Twist tests were conducted according to three different methods for various length/thickness and span/plate diagonal ratios, and the shear modulus corresponding to each test condition was obtained. To examine the validity of shear modulus obtained by these tests, asymmetric four-point bending tests and finite element calculations were independently conducted and the results were compared. Specimens had a length/thickness ratio greater than 47 and were supported at two or three points close to each corner while applying a load to the remaining corner. Under these conditions, the shear modulus could be properly obtained over a wide range of span/plate diagonal ratios.
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August 1, 2006
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Changes in the dielectric relaxation due to water adsorbed on eight types of chemically treated woods, as well as untreated wood ( Picea sitchensis Carr.), with moisture content (MC) were investigated in the temperature range between −150°C and 20°C and in the frequency range between 100 Hz and 1 MHz. Cole-Cole's circular arc law was applied to the results of dielectric measurements conducted at seven levels of relative humidity (RH), and the relaxation spectra at −75°C were calculated. The theory of rate processes was applied to the dielectric relaxation resulting from the motions of water molecules adsorbed on the untreated and chemically treated woods, and the binding state of adsorbed water was examined. The relaxation magnitude increased with increasing MC, irrespective of the chemical treatment. The distribution of relaxation times decreased in the MC range below 1%, but increased with increasing MC at higher levels. The generalized relaxation time increased up to 5% MC, then decreased. The enthalpy-entropy compensation phenomenon was observed in the dielectric relaxation, which was derived from the adsorption of water molecules on the chemically treated woods. The binding states of adsorbed water and ice were similar. The water molecules adsorbed on wood may have produced a very wide variety of cohesive structures in the chemically treated woods.
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Static and dynamic rheological analyses using time/temperature equivalence were applied to freestanding poly(vinyl acetate-co-NMA) adhesive films and to wood-bonded films (composites), which were completely dry in all cases. Films and composites were prepared with two types of cross-linking: (1) cross-linking through AlCl 3 catalysis of N -methylolacrylamide (NMA) comonomer; and (2) additional cross-linking using a resol phenolic (PF) additive, in addition to AlCl 3 catalysis. Rheological experiments revealed that accelerated weathering (AW) significantly modified the mechanical response of films and composites lacking the PF additive. For samples lacking PF fortifier, AW caused a new thermal transition appearing as a major mechanical softening in the long time domain (creep master curves) or in the low-frequency region (dynamic master curves). This new transition correlated to a performance loss found with fracture testing in a previous publication. Here, the static and dynamic rheological data indicated that the AW-induced softening was a reversible transition. Differential scanning calorimetry analysis and the manipulation of physical aging effects demonstrated that the AW-induced softening was a glass transition. The calorimetric weakness and temperature of this transition indicated that it corresponds to the T g of poly(vinyl alcohol) (PVOH), which is the emulsion polymerization interfacial agent. In contrast, all PF-formulated samples displayed only the base polymer T g . Therefore, the PF additive prevented weathering effects that lead to PVOH softening. Atomic force and scanning electron microscopy provided visual evidence of the action of PF on PVOH at interparticle boundaries. We suggest that the PF fortifier enhances latex durability through the formation of hydrolytically stable PVOH cross-links at the interparticle boundaries.
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August 1, 2006
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Anisotropy of acoustic propagation velocities is a ubiquitous feature of wood. This needs to be considered for successful application of travel time tomography, an increasingly popular technique for non-destructive testing of living trees. We have developed a simple correction scheme that removes first-order anisotropy effects. The corrected travel-time data can be inverted with isotropic inversion codes that are commercially available. Using a numerical experiment, we demonstrate the consequences of ignoring anisotropy effects and outline the performance of our correction scheme. The new technique has been applied to two spruce samples. Subsequent inspection of the samples revealed a good match with the tomograms.
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August 1, 2006
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Longitudinal surface strain was measured or estimated using three different methods along the stems of nine trees of 10-year-old Eucalyptus globulus Labill. Wood samples were collected close to the location where the strain was measured or estimated. Microfibril angle (MFA), cellulose crystallite width ( W cryst ), microdensity and Young's modulus along the grain ( E L ) were determined using the SilviScan-2 technology at high spatial resolution. Relationships of measured strain and estimated strain to wood properties were established. The quality of the relationships depends on a particular wood property. Strain was more closely related to mean W cryst than to any other wood properties. Its relationship with MFA was the next closest. Based on the results of regression analysis, we propose that W cryst may be suitable for the prediction of surface strain at a moderate level of reliability. Adding measurement of MFA, microdensity and E L does not significantly improve the prediction quality. The strain measurement method also affects the results. The best relationships were obtained with longitudinal displacement measured by the CIRAD method. Strain measured by the strain gauge method gave weak relationships, possibly owing to variation in the cambium age of the specimens.
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