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1.
Summary By measuring the proton spin–lattice relaxation times (T1H) in the solid-state for black spruce softwood, the molecular mobilities of carbohydrates and lignin have been evaluated as
a function of pH. These studies have shown that the mobility of the polymeric constituents of wood is affected by the ionization
of the different functional groups at different pH's. The analyses of the proton-spin–lattice relaxation time data at constant
humidity revealed that the maximum T1H for both carbohydrates and lignin occurs at about neutrality, while it was found to be depressed at the two extremes of the
pH range. By treating a wood sample with propylene oxide, the esterification of the acid groups was affected, thus deactivating
the ionization process and their contribution to T1H. The experimental T1H values for cellulose and lignin after the esterification were significantly decreased at pH 6 confirming that their ionization
plays a very significant role in determining chain mobility.
Received 1 December 1998 相似文献
2.
Brauns’ lignins present in the methanol extracts of fresh birch (Betula pendula) xylem and of sawn birch board subjected to vacuum drying were characterized by 1H and 13C NMR spectroscopy (1D and 2D), IR spectroscopy, gel permeation chromatography (GPC) and colour measurements (CIELab) in order to find out whether Brauns’ lignin could contribute to the colour change of sawn timber that occurred during vacuum drying. The two Brauns’ lignin samples contained about equal amounts of syringylpropane and guaiacylpropane units linked with β-O-4 and β–β side-chain structures. Molecular weight of the Brauns’ lignin of vacuum-dried birch board (acetylated: 5,200 g mol−1) was higher than that of the Brauns’ lignin of fresh birch wood (acetylated: 4,400 g mol−1). The Brauns’ lignin of vacuum-dried wood was also clearly darker and more prominently yellow and red;
between the Brauns’ lignin samples was 23.59. The differences in the molecular weights and colours suggest that the Brauns’ lignin underwent a chemical change during vacuum drying of the wood and that this change may have affected the colour of the wood. 相似文献
3.
In this study heartwood from a Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] plantation was treated using a high-temperature drying (HTD) method at 115°C, a low-temperature drying (LTD)
method at 65°C, and freeze vacuum drying (FVD), respectively. The dynamic viscoelastic properties of dried wood specimens
were investigated. The measurements were carried out at a temperature range of −120 to 250°C at four different frequencies
(1, 2, 5, and 10 Hz) using dynamic mechanical analysis (DMA). We have drawn the following conclusions: 1) the storage modulus
E′ and loss modulus E″ are the highest for HTD wood and the lowest for FVD wood; 2) three relaxation processes were detected in HTD and LTD wood,
attributed to the micro-Brownian motion of cell wall polymers in the non-crystalline region, the oscillations of the torso
of cell wall polymers, and the motions of the methyl groups of cell wall polymers in the non-crystalline region in a decreasing
order of temperatures at which they occurred; and 3) in FVD wood, four relaxation processes were observed. A newly added relaxation
is attributed to the micro-Brownian motions of lignin molecules. This study suggests that both the HTD and the LTD methods
restrict the micro-Brownian motion of lignin molecules somewhat by the cross-linking of chains due to their heating history.
__________
Translated from Journal of Beijing Forestry University, 2008, 30(3): 96–100 [译自: 北京林业大学学报] 相似文献
4.
Proton magnetic resonance techniques for characterization of water in wood: application to white spruce 总被引:3,自引:0,他引:3
C. D. Araujo A. L. MacKay J. R. T. Hailey K. P. Whittall H. Le 《Wood Science and Technology》1992,26(2):101-113
Summary Two new proton magnetic resonance techniques, relaxation spectra and relaxation selective imaging, have been used to investigate the distribution of water in samples of normal white spruce sapwood, heartwood, and juvenile wood as well as two rehydrated heartwood samples containing incipient decay and compression wood respectively. It is demonstrated that the spin-spin (T2) relaxation behavior in wood is best presented as a continuous spectrum of relaxation times. Spectra of T2 for white spruce show separate peaks corresponding to the different water environments. Bound water gives a peak with an T2 time of about 1 ms and lumen water gives a distribution of T2 times in the range of 10 to 100 ms. The lumen water T2 time is a function of the wood cell radius. Consequently, the different cell lumen radii distributions for spruce sapwood, juvenile wood, and compression wood are readily distinguishable by the shape of their T2 spectra. Water environments which are separable on a T2 spectrum may be imaged separately. Imaging has been carried out in one dimension for bound water and lumen water of a spruce sapwood sample at four different moisture contents ranging from 100% to 17%. For the first time, we demonstrate that above the fibre saturation point the moisture density profile of the bound water is largely independent of moisture content. The feasibility and utility of using these techniques for internal scanning of logs and lumber is discussed. These techniques should provide new insights into the wood drying process.We would like to thank Michael Weiss of the Biological Science Electron Microscopy Facility at the University of British Columbia for his assistance with the microscopy and image analysis. This research was supported by grants from the Natural Sciences and Engineering Research Council of Canada and the Canadian Forestry Service 相似文献
5.
Chemical reactivity of heat-treated wood 总被引:1,自引:0,他引:1
Chemical reactivity of heat-treated wood was compared with that of untreated wood. For this purpose, heat-treated pine or
beech sawdust was reacted with different carboxylic acid anhydrides in pyridine or with phenyl isocyanate in dimethyl formamide.
Compared to controls, weight gains obtained with heat-treated sawdust are smaller showing a lower chemical reactivity. FTIR
analyses of lignin and holocellulose fractions, isolated after acidic hydrolysis of polysaccharides or delignification with
sodium chlorite, indicate that both components are involved in the reactions. Compared to lignin, holocellulose exhibits important
infrared absorptions of about 1,730 cm−1, characteristic of ester or urethane linkages formed. Lower reactivity of heat-treated sawdust is explained by the decrease
in free reactive hydroxyl groups in holocellulose due to the thermal degradation of hemicelluloses, considered more reactive
than cellulose. 相似文献
6.
Lignin characteristics of bast fiber and core in kenaf, bark and wood of paper mulberry and mulberry
The structural features of bast fiber and core lignins in kenaf (Hibiscus cannabinus), bark and wood lignin of paper mulberry (Broussonetia papyrifera (L.) Vent × Broussonetia kazinoki Sieb.) and mulberry (Morus bombycis) were characterized by alkaline nitrobenzene oxidation, ozonation and methoxyl group determination. Bj?rkman lignins were
isolated from bast fiber and core, and bark and wood fractions of the plant samples, and structural characteristics were investigated
by 1H NMR and 13C NMR spectroscopies. Kenaf bast fiber gave very high molar ratio of syringaldehyde to vanillin (S/V) of alkaline nitrobenzene
oxidation products, while methoxyl content was about the same as that of the core fraction. Results of 1H NMR and 13C NMR of Bj?rkman lignin suggested the presence of aliphatic fragments in lignins isolated from paper mulberry and mulberry
bark, but not in kenaf bast fiber. The lower yield of alkaline nitrobenzene oxidation products from bast fiber and bark might
be due to the higher content of condensed structure of lignin compared to core fraction. Total yield of erythronic (E) and threonic (T) acids of ozonation products and the molar ratio of erythronic acid to threonic acid (E/T) of the bast fibers and bark were lower than the corresponding core and wood fractions, suggesting that the contents of arylglycerol-β-aryl
ether intermonomer linkages in the bast fiber and bark lignin were lower than those of the core and wood fractions. Methoxyl
content of bark lignin was lower than the corresponding wood lignin. The methoxyl content of the extract-free kenaf bast fiber
was similar to that of the core fraction, while the values of paper mulberry and mulberry bark were about one-half of the
corresponding wood fractions, respectively. In bark lignins, the methoxyl contents of Klason lignin and Bj?rkman lignin from
bark were lower than those of the extract-free barks. This result suggests that the purity of Klason lignin and Bj?rkman lignins
of bark may be rather low. 相似文献
7.
8.
Eight different residual lignins isolated from unbleached chemical pulps [sulfite, kraft, alkaline sulfite-anthraquinone-methanol
(ASAM), soda/AQ/MeOH] of spruce and beech were characterized using gel permeation chromatography (GPC), thioacidolysis, and
desulfurization to determine average molecular weight, amounts of uncondensed β-O-4 linkages, and dimeric linkage patterns, respectively. The total amounts of G-CHSEt-CHSEt-CH2SEt and S-CHSEt-CHSEt-CH2SEt were markedly reduced in residual lignins to 40% to 80% of the values for the corresponding milled wood lignins (MWLs).
The number of dimeric units determined by thioacidolysis and desulfurization of the residual lignins was decreased by onehalf
to one-fifth compared to the MWLs. Among the diverse types of dimeric units, reduction of β-1 and β-5 units was significant in most of the residual lignins, with the exception of beech ASAM residual lignin. Compared to beech
MWL, 40% more C6–C3 main monomers were detected, whereas the relative composition of the dimeric units in the beech residual
lignin was very similar to that in the beech MWL. The average molecular weights of residual lignins were less than those of
the MWLs. However, the average molecular weights of the spruce kraft and soda residual lignins were determined to be higher
than those of the corresponding MWLs. 相似文献
9.
Chemical changes in cell wall components of bamboo internode during steam explosion process were analyzed to investigate self-binding
mechanism of binderless board from steam-exploded pulp. More than 30% of xylose on initial mass, which is a major hydrolyzate
of bamboo hemicelluloses, was lost after steam explosion treatment. Bamboo lignin is characterized by the presence of ester-
and/or ether-linked p-coumaric acid to lignin. The content of phenolic hydroxyl groups of lignin isolated from steam-exploded pulp was characterized
2.3 times higher than those of the extract-free bamboo internode due to the cleavage of β-O-4 linkages. Alkaline nitrobenzene
oxidation of the bamboo lignin gave vanillin, syringaldehyde and p-hydroxybenzaldehyde as major products. The content of p-hydroxybenzaldehyde decreased after steam explosion treatment, indicating the cleavage of ester- and/or ether-linked p-coumaric acid. The total yield of erythronic and threonic acids in ozonation products of the extract-free bamboo internode
lignin was 268 mmol (200 g lignin)−1, while those of lignins in the steam-exploded pulp and powdery fraction were 96 and 129 mmol (200 g lignin)−1, respectively, suggesting the significant cleavage of β-O-4 linkages during steam explosion treatment. The cleavage of β-O-4
linkages was also confirmed by 1H- and 13C-NMR spectroscopic observations. 相似文献
10.
Test samples of Japanese larch (Larix leptolepis) heartwood and Japanese beech (Fagus crenata) sapwood were heated for 22 h at constant temperatures (50°–180°C) under three water content conditions. Raman spectra of
the samples were recorded before and after the heat treatments, and spectral changes in the range from 1000 cm−1 to 1800 cm−1 were evaluated using the difference spectrum method. For both wood species, the Raman band intensity at 1655–1660 cm−1 due mainly to the C=C and C=O groups in lignin clearly decreased with increasing heat-treatment temperature (HTT). The spectral
change was thought to reflect the progress of condensation reactions of lignin molecules during the heat treatment. Moreover,
the decrease in band intensity was considerably facilitated by the presence of water in the cell wall, suggesting that the
condensation is closely related to the softening of lignin. From the spectral changes in the wavenumber region of 1200–1500 cm−1, it was considered that wood constituents are partially decomposed at the higher HTT.
Part of this article was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, March 2003 相似文献
11.
Thermoplastic processing of lignin is restricted by its high glass transition temperature (T g). In this study, lignin was modified with polyethylene glycol (PEG) during steam explosion to improve its thermoplastic properties, and the effects of steam explosion and PEG on the chemical structure and thermal properties of lignin were investigated. Structure characterization using Fourier transform infrared spectroscopy showed that hydroxyl and ether functional groups increased and the activity of lignin was improved by steam explosion. In addition, steam explosion treatment was more effective than heat treatment for promoting the reaction of PEG with lignin. Solid-state 13C NMR revealed that PEG was grafted onto lignin. The T g of raw lignin was 164.1 °C; after steam explosion, lignin exhibited more than one T gs. The T g of lignin was reduced when the steam explosion temperature increased and decreased further, to around 60 °C, when PEG was used to modify lignin. Therefore, this work provides an effective approach to reducing the high T g of lignin. 相似文献
12.
Hiroto Homma Hirofumi Shinoyama Yukihiro Nobuta Yoshie Terashima Seigo Amachi Takaaki Fujii 《Journal of Wood Science》2007,53(1):80-84
Strobilurus ohshimae is an edible mushroom, and it specifically forms its fruiting bodies on buried sugi (Cryptomeria japonica) twigs. In this research, we studied lignindegrading activity of S. ohshimae. We isolated 18 strains of S. ohshimae from various regions of Japan, and determined their lignin degradation rates on sugi wood meal medium. All the strains of
S. ohshimae degraded approximately 6%–12% of sugi lignin in 30 days, and these lignin degradation rates were 1.5–3 times higher than those of Trametes versicolor, which is a typical lignin-degrading fungus. Among the three main lignin-degrading enzymes, activity of lignin peroxidase
and manganese peroxidase was not observed, while 4340U/g of laccase was produced in 30 days. To investigate the effect of
wood species on lignin degradation by S. ohshimae, the lignin degradation rate and laccase productivity on sugi wood meal medium were compared with those on beech (Fagus crenata). In T. versicolor, both lignin degradation rate and laccase productivity were higher on beech than on sugi. Conversely, in S. ohshimae, lignin degradation rate and laccase productivity were higher on sugi than on beech. Therefore, it was suggested that coniferous lignin is not always difficult to degrade for the fungi that inhabit
softwood.
Part of this article presented at the 54th Annual Meeting of the Japan Wood Research Society, Sapporo, August 2004 相似文献
13.
Eveliina Hiltunen Kirsi Mononen Leila Alvila Tuula T. Pakkanen 《Wood Science and Technology》2008,42(2):103-115
A discolouration that appeared on the surfaces of a European white birch (Betula pubescens) board during vacuum drying was studied by means of colour measurements (CIEL*a*b*), elemental analysis and the analysis of extractives. The discoloured surface layer of the dried board contained substantially
more methanol-soluble extractives than did the light-coloured part (50.7 mg g−1 vs. 26.7 mg g−1 dry wood), and the colour difference (ΔE*
ab
20.0) between the two extracts was notable. Characterization by means of GC and 13C NMR spectroscopy showed that the extracts contain sugars (mainly glucose and fructose), low-molecular-weight phenolic compounds,
proanthocyanidins, Brauns’ lignin and fatty acid esters. Concentrations of sugars, low-molecular-weight phenols, proanthocyanidins
and Brauns’ lignin were higher in the discoloured surface layer than in the light-coloured part. The yellowness of the surface
layer was associated with the accumulation of low-molecular-weight phenolic extractives, and the redness with Brauns’ lignin
and possibly proanthocyanidins. 相似文献
14.
Experimental determination of the convective heat and mass transfer coefficients for wood drying 总被引:1,自引:1,他引:0
The knowledge of the convective heat and mass transfer coefficients is required for the characterization of the boundary
conditions of the heat and mass transfer equations of a wood drying model based on water potential. A new experimental method
for the determination of the convective mass transfer coefficient is presented. This method is based on the measurement of
the moisture content, and indirectly the water potential, at the surface of a wood specimen at different drying times. Drying
experiments were performed on red pine (Pinus resinosa Ait.) sapwood from nearly saturated to dry conditions at 56 °C, 52% relative humidity and air velocities of 1.0, 2.5 and
5.0 m s−1. The results show that the convective mass transfer coefficient is constant until the wood surface moisture content reaches
about 80% and then decreases more or less gradually as the moisture content decreases further. The convective mass transfer
coefficient increases with air velocity. A regression analysis shows that there is no significant improvement in considering
the water potential gradient near the wood surface when the difference in water potential between the surface and the surrounding
air (ψs − ψ∞) is used to determine the convective mass flux at the surface. Also, ψs − ψ∞ is more appropriate than the water vapour pressure difference (pvs − pv∞) as the responsible driving force of the moisture flux leaving the wood surface. The convective heat transfer coefficient
was determined during the same experiments. A plateau is observed at high values of moisture content corresponding to the
constant drying rate period.
Received 27 February 1998 相似文献
15.
Petia S. Nikolova Stephan Raspe Christian P. Andersen Raphael Mainiero Helmut Blaschke Rainer Matyssek Karl-Heinz Häberle 《European Journal of Forest Research》2009,128(2):87-98
We present a field study on the drought effects on total soil respiration (SRt) and its components, i.e., “autotrophic” (SRa: by roots/mycorrhizosphere) and “heterotrophic” respiration (SRh: by microorganisms and soil fauna in bulk soil), in a mature European beech/Norway spruce forest. SRa and SRh were distinguished underneath groups of beech and spruce trees using the root exclusion method. Seasonal courses of SRa and SRh were studied from 2002 to 2004, with the summer of 2003 being extraordinarily warm and dry in Central Europe. We (1) analyzed
the soil temperature (T
s) and moisture sensitivity of SRa and SRh underneath both tree species, and (2) examined whether drought caused differential decline of SRa between spruce and beech. Throughout the study period, SRa of beech accounted for 45–55% of SRt, independent of the soil water regime; in contrast, SRa was significantly reduced during drought in spruce, and amounted then to only 25% of SRt. In parallel, fine-root production was decreased during 2003 by a factor of six in spruce (from 750 to 130 mg l−1 a−1), but remained at levels similar to those in 2002 in beech (about 470 mg l−1 a−1). This species-specific root response to drought was related to a stronger decline of SRa in spruce (by about 70%) compared to beech (by about 50%). The sensitivity of SRa and SRh to changing T
s and available soil water was stronger in SRa than SRh in spruce, but not so in beech. It is concluded that SRa determines the effect of prolonged drought on the C efflux from soil to a larger extent in spruce than beech, having potential
implications for respective forest types.
This article belongs to the special issue "Growth and defence of Norway spruce and European beech in pure and mixed stands." 相似文献
16.
To analyze the effects of lignin on the destabilization of wood due to quenching, we examined the dielectric properties of
untreated and delignified wood before and after quenching at 20°C from 50 Hz to 100 MHz. For untreated wood, the inflection
points of log ε′ and log σ vs log f and the peak of log(tan δ) vs log f were attributed to interfacial polarization before quenching, and the location of the inflection point shifted to a higher
frequency with increasing moisture content because of changes in the water cluster. After quenching, the inflection points
of log ε′ and log σ and the peak of log(tan δ ) shifted to higher frequency; however, the values of log ε′, log σ recovered to those before quenching with the passage of time. For delignified wood, dielectric relaxation was observed at
a higher frequency than for untreated wood irrespective of quenching. It was inferred that the mobility of water molecules
was influenced by the cluster surroundings because of increased number of adsorption sites in hemicellulose. Moreover, after
quenching, the recovery process did not change greatly over time; it was shown that the matrix structure was affected more
by quenching with the loss of lignin. 相似文献
17.
Heat-induced colour changes of pine (Pinus pinaster) and eucalypt (Eucalyptus globulus) wood 总被引:4,自引:0,他引:4
Bruno Esteves António Velez Marques Idalina Domingos Helena Pereira 《Wood Science and Technology》2008,42(5):369-384
Heat treatment of Pinus pinaster and Eucalyptus globulus wood was carried out by hot air in an oven for 2–24 h at 170–200°C and by steam in an autoclave for 2–12 h at 190–210°C.
The colour parameters L*, a* and b* were determined by the CIELAB method on radial, tangential and transverse sections of untreated and treated wood, and their
variation with regard to the treatment (ΔL*, Δa* and Δb*) were calculated in percent. For untreated eucalypt wood, lightness (L*) varied between 54.1 and 63.8% with a* between 7.4 and 8.5, and b* between 15.7 and 19.9. For untreated pine wood, L* varied between 67.3 and 76.1%, a* between 6.9 and 7.6 and b* between 16.3 and 24.1. Oven heat-treated wood became darker (ΔL* about 50% for 4% mass loss), and this was more for eucalypt wood under the same treatment conditions. In general, the contribution
of red (a*) and yellow (b*) colour decreased with heat treatment. The transverse section of the two species darkened less for both the treatments with
small differences between radial and tangential sections. Lightness decrease was related to chemical changes; with good correlations
with glucose (R
2 = 0.96), hemicelluloses (R
2 = 0.92) and lignin (R
2 = 0.86). As regards colour, the heat treatments showed an interesting potential to improve the wood quality for solid timber
products from pine and eucalypt. 相似文献
18.
For a better understanding of the binding between silicon dioxide and wood as well as the dielectric properties of silicon
dioxide/wood composite, dielectric relaxation was measured for untreated wood [Cunninghamia lanceolata (Lamb.) Hook] and for silicon dioxide/wood composite with different weight percentage gain (WPG). Cole–Cole’s circular arc
law, distribution spectrum of relaxation time and relation model were applied to the results of relaxation due to motions
of the methylol groups. The results were as follows. The generalized relaxation time and ε
s
− ε
∞
decreased with increasing WPG. The distribution spectrum of relaxation time decreased more and more and broadened with increasing
WPG. The methylol group in the amorphous region of the wood cell wall participated in hydrolysis reaction and condensation
reaction caused by tetraethylorthosilicate (TEOS), and there is a cross-link between silicon dioxide and wood. The value of
apparent activation energy (ΔE) increased for silicon dioxide/wood composite, and increased with increasing WPG. Activation enthalpy (ΔH) and activation entropy (ΔS) increased, while activation free energy (ΔG) decreased with increasing WPG. The number of hydroxyl groups cut in dielectric relaxation increased with increasing WPG. 相似文献
19.
Compressive deformation of wood impregnated with low molecular weight phenol formaldehyde (PF) resin III: effects of sodium chlorite treatment 总被引:1,自引:0,他引:1
To obtain high-strength phenol–formaldehyde (PF) resin-impregnated compressed wood at low pressing pressure, we investigated the effects of sodium chlorite (NaClO2) treatment on wood prior to low molecular weight PF resin impregnation. Sawn veneers of Japanese cedar (Cryptomeria japonica) were treated with 2% aqueous NaClO2 solution at 45°C for 12 h to remove lignin, and the process was repeated up to four times, resulting in weight loss of 21%. NaClO2 treatment has shown considerable potential for high compression of PF resin-impregnated wood at low pressing pressure, especially after adding moisture to a content of 10%–11%. This deformation is further enhanced during pressure holding by creep deformation. The density, Young’s modulus, and bending strength of PF resin-impregnated veneer laminated composites that were treated with NaClO2 four times and compressed at 1 MPa, reached 1.15 g/cm3, 27 GPa, and 280 MPa, respectively. The values in untreated PF resin-impregnated wood reached 0.8 g/cm3, 16 GPa, and 165 MPa, respectively. 相似文献
20.
Goddert von Oheimb Christina Westphal Werner Härdtle 《European Journal of Forest Research》2007,126(3):359-370
The diversity, spatial patterns and temporal dynamics of dead wood were examined within the near-natural beech forests (Fagus sylvatica) of Serrahn (North-eastern Germany). Data were collected in an 8 ha sample plot and in two permanent plots (0.36 and 0.25 ha)
that had been established at the end of the 1960s. The mean volume of dead wood was 94 m3 ha−1, amounting to 14% of the total volume of all trees. The dead wood displayed a large variation in dead wood type, tree size
and decay class. Standing dead wood accounted for about one-third of the total dead wood volume. The densities of standing
dead trees were about 10% of the densities of the living trees over a wide range of diameters. The overall spatial distribution
of dead trees exhibited a random pattern. Among the different dead wood types, standing entire dead trees and uprooted trees
deviated from this pattern by displaying a significantly aggregated pattern. In the permanent plots a high mortality of overstorey
trees was observed (1.3% year−1) and the average amount of dead wood increased greatly from 2.9 to 111.6 m3 ha−1 over the 35-year observation period. The near-natural beech forests of Serrahn have experienced a long period of low human
interference. Nevertheless, our results suggest that the structure and dynamics of dead wood are strongly affected by the
last major disturbance events that took place at the end of the Middle Ages. Information about the forest history is therefore
a basic requirement when interpreting the results obtained in near-natural forests. 相似文献