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Dietrich Fengel 《Wood Science and Technology》1970,4(1):15-35
Summary During the delignification of wood several processes overlap one another. One of these is the penetration of the wood samples by the delignifying solution. Penetration tests under different conditions show that there is almost no difference in the penetration depth of wood samples penetrated by diffusion only and of wood samples treated with pressure. In both cases the pits are closed during the flow of fluids. Vacuum treated samples show better penetration and most of the pits in these samples remain open. The distribution of fluids within the cell walls takes place in the intercellular spaces, in small openings in the compound middle lamella and in the secondary wall 1 as well as in very fine pores in the secondary wall 2. The penetration of a wood sample is greatly facilitated if the sample is mechanically injured. A slowly proceeding delignification with ethylene sulphite shows that the delignification obviously starts in the S 1 layer and proceeds from there towards the compound middle lamella and the S 2 layer. In the first stages of lignin removal the compound middle lamella is also attacked, the attack beginning at the border of the pit chambers. 相似文献
3.
Gu-Joong Kwon Shigenori Kuga Keko Hori Mitsuyoshi Yatagai Keisuke Ando Nobuaki Hattori 《Journal of Wood Science》2006,52(5):461-465
Pyrolysis of cellulose was studied for the purpose of practical production of 1,6-anhydro-β-D-glucopyranoside (levoglucosan, LG). To minimize secondary degradation of levoglucosan, two methods were examined: (1) conductive
heating by glass bottle, and (2) radiation heating from the surface by CO2 laser beam, both under vacuum and in a nitrogen atmosphere. Glass-bottle pyrolysis under vacuum gave levoglucosan yield of
50%–55% in the optimum temperature range of 350°–410°C, where placing the cold trap in the vicinity of heated area was effective
in improving the yield. In contrast, glass-bottle pyrolysis under nitrogen gave low yields of 17%–20%, probably due to slower
diffusion of pyrolysis product from hot region. The CO2 laser pyrolysis under vacuum gave the product as aerosol (white smoke), causing difficulty in recovery of the product, and
the maximum yield was 5%–17%. In this case the treatment under nitrogen flow was effective for recovery of aerosol, and the
maximum yield reached approximately 25%. 相似文献
4.
Dietrich Fengel 《Wood Science and Technology》1969,3(3):203-217
Summary Since in these studies wood is used as basic material for the isolation of cellulose the structure and the composition of this planty substance were considered in greater detail. New measurements of the fiber dimensions and the thickness of the cell wall layers of typical springwood and summerwood tracheids in combination with data obtained from literature led to a model showing the most probable distribution of cellulose, polyoses, and lignin within the cell wall. The ultrastructural composition of the wood cell wall has been deduced from the properties and the behaviour of the cell wall components. The described model will be the basis for subsequent considerations.
Dedicated in appreciation to my esteemed teacher Prof. Dr.-Ing. Georg Jayme, on the occasion of his 70th birthday. 相似文献
Zusammenfassung Da bei diesen Untersuchungen Holz das Ausgangsmaterial zur Isolierung von Cellulose bildet, wurden die Struktur und die Zusammensetzung dieser pflanzlichen Substanz näher betrachtet. Neue Messungen der Faserdimensionen und der Dicke der einzelnen Wandschichten typischer Früh- und Spätholztracheiden in Verbindung mit Literaturwerten führten zu einem Modell, das die wahrscheinlichste Verteilung von Cellulose, Polyosen und Lignin innerhalb der Zellwand zeigt. Die ultrastrukturelle Zusammensetzung der verholzten Zellwand wurde aus den Eigenschaften und dem Verhalten der Zellwandkomponenten abgeleitet. Das beschriebene Modell wird die Grundlage für nachfolgende Betrachtungen bilden.
Dedicated in appreciation to my esteemed teacher Prof. Dr.-Ing. Georg Jayme, on the occasion of his 70th birthday. 相似文献
5.
Mariko Yoshioka Katsuya Okajima Tomoko Miyazaki Nobuo Shiraishi 《Journal of Wood Science》2000,46(1):22-31
A plasticization method for cellulose acetates (CAs) has been developed that is based on the reaction with dibasic acid anhydrides and monoepoxides during the melting processing. As a continuation of the discussion in the previous report, additional evidence is presented for the role of grafting oligoesters onto cellulose acetates to prevent the bleeding of homo-oligoesters from the inside of molded articles to their surface. Based on these results, a method for enhancing the amount of grafting has been pursued by varying the combination of dibasic acid anhydrides and monoepoxides. The resulting reactive meltprocessing method allows preparation of biodegradable cellulosic plastics using practical process conditions. Higher biodegradability has been found for the oligoester-grafted CAs than for the unmodified parent CAs. 相似文献
6.
Enzymatic degradation of cellulose,cellulose derivatives and hemicelluloses in relation to the fungal decay of wood 总被引：1，自引：0，他引：1
Summary Cellulases and hemicellulases (mannanase and xylanase) from culture filtrates of various fungi, including a brown rot fungus, Polyporus schweinitzii and a soft rot fungus, Chaetomium globosum, have been isolated and characterized. Investigations of their molecular weights, pH- and temperature optima and stabilities indicate that hydrolases of the wood destroying fungi are very similar to one another and to hydrolases from various other plant organisms. Substrate specificities and the effect of substituents on the natural substrates have also been investigated. Routine tests for mannanase and xylanase were carried out with model substrates (mannan from Tubera salep, xylan from wheat straw), but preliminary tests with complex hemicelluloses isolated from wood showed that these too could be broken down to monoor oligosaccharides. The results presented are discussed in relation to possible roles of the various enzymes in vivo.Paper presented at the Int. Wood Chemistry Symposium, Seattle, 3. IX. 1969.With support of the Deutsche Forschungsgemeinschaft. 相似文献
7.
纤维素是植物细胞壁的主要组分之一,是由葡萄糖通过1,4-β糖苷键连接而成的均一聚糖,广泛应用于生产酯类、醚类等纤维素基化工产品。纤维素基产品的制备及应用与其溶解程度密切相关,探究纤维素溶解机理,寻找一种绿色高效的纤维素溶剂至关重要。综述了当前国内外学者们对纤维素溶解机理的解释(氢键破坏理论)以及可能影响溶解的因素(化学热力学、化学动力学、结晶度、纤维素两亲性、电荷数和温度),在此基础上探讨了导致纤维素水溶性差的原因,提出了在复杂体系中除了氢键作用以外,还需要综合考虑范德华力、疏水性相互作用的影响。同时,总结了纤维素在离子液体中溶解机理方面存在的争议,其中关于氢键理论还存在一定问题,动力学控制理论尚不明确,阳离子在溶解过程所起的作用被忽视,指出离子液体阳离子的两亲性是纤维素溶解的关键因素。基于纤维素的两亲性及两亲性溶剂促进纤维素溶解的重要理论,提出了应重点寻找新型两亲性溶剂的观点,为未来寻求高效、环境友好、成本低廉的纤维素溶剂指明了方向。 相似文献
8.
Summary Crystallization experiments starting from highly concentrated solutions of cellulose in trifluoroacetic acid (TFA) resulted
in white crystalline particles with diameters of as much as 0.5 mm. The plate-like particles consist of lamellae arranged
perpendicular to the surface. The lamellae are grown from thin scale-like platelets showing clear diffraction reflexes and
an internal parallel structure. Parallel structures were also detected in partially hydrolyzed cellulose. It is concluded
that cellulose chains of low DP tend to rearrange themselves by a side by side accumulation of extended molecules. 相似文献
9.
Yoshiharu Nishiyama 《Journal of Wood Science》2009,55(4):241-249
The current structural models of the cellulose microfibril as well as its mechanical and thermal properties are reviewed.
The cellulose microfibril can be considered as a single thin and long crystalline entity with highly anisotropic physical
properties. The contribution and limit of different methods employed such as electron microscopy, infrared spectroscopy, X-ray
scattering and diffraction, solid state nuclear magnetic resonance spectroscopy, and molecular modeling are also discussed. 相似文献
10.
The behaviors of cellulose (commercially available filter paper) were investigated in glow-discharge plasma, where pyrolysis does not occur because of low temperatures. Cellulose filter papers were decomposed in a glow-discharge plasma with nitrogen flow even at low temperatures of around 50 °C and disappeared completely after a treatment of approximately 90 h without char formation. Tar formation was not observed on any surfaces inside the plasma chamber and vacuum lines. Hence, it was concluded that all cellulose was decomposed into gaseous products. An in-situ analysis of gaseous products by quadrupole mass spectrometry suggested the formation of H2, H2O, CO and CO2 from cellulose. These findings indicate that a clean and complete gasification of cellulose can be achieved with glow-discharge plasma. 相似文献
11.
Use of a fundamental concept, henceforth referred to as the scission fraction of cellulose unit (SFCU), was suggested to
clarify the cleavage reactivity of cellulose during oxygen delignification (OD). According to the SFCU theory, the cleavage
activity of pulp cellulose remains relatively undisturbed provided the experimental conditions are maintained regardless of
pulp origin. SCFU is a universal variable for evaluating how processes and additives affect the degree of pulp cellulose degradation.
Specifically in this study, the effects of the protector additives MgSO4 and phenol on the oxygen delignification (OD) process were investigated. Both phenol and MgSO4 retard the cleavage rate of the cellulose chain, but the retarding effect of MgSO4 is greater than that of phenol. Phenol alone cannot significantly improve the selectivity of the OD process, whereas MgSO4 can decrease the cleavage rate of cellulose and increase the selectivity of OD. Moreover, synergistic selectivity enhancement
for pulp using a combination of MgSO4 and phenol was observed. The protective effect of various chemical protectors was additive, whereas the retarding effect
on delignification was not.
Received: December 21, 2001 / Accepted: July 22, 2002
Acknowledgments We acknowledge the member companies of the Institute of Paper Science and Technology whose interest drives most of our research
efforts. Additionally, we gratefully acknowledge the Department of Energy (grant DE-FC07-02ID14261) whose support has made
part of this work possible. 相似文献
12.
Yong Sun Lu Lin Haibo Deng Hong Peng Jiazhe Li Runchang Sun Shijie Liu 《Frontiers of Forestry in China》2008,3(4):480-486
Bamboo fiber dissolution and hydrolysis in formic acid were studied. After hydrolysis, formic acid can be recovered in a clean
state and reused. Solid water-soluble sugars were obtained. After being dipped into the formic acid solution for 30 min, the
bamboo fibers started to swell. After one hour, the bamboo fibers gradually started to dissolve in the formic acid solution.
The color of the liquor/solution turned green and dark. In the end, the bamboo fibers became thoroughly dissolved in the liquor
after four hours. There was a clear hierarchical tissue structure on the fiber surface, as observed by AFM before treatment.
The differential structure disappeared after 30 min of treatment. The fiber surface became plump and glossy. After six hours
reaction at 60°C, the solid sugar mixture recovered contained glucose, cellobiose, cellotriose, cellotetrose, cellopentose
and cellohexaose. A significant fraction of the sugar products consisted of monomeric glucose. More than 54.5% of the bamboo
fiber mass had been transformed into monomeric glucose.
__________
Translated from Biomass Chemical Engineering, 2007, 41(2): 5–10 [译自: 生物质化学工程] 相似文献
13.
L. A. Donaldson 《Wood Science and Technology》1988,22(1):33-41
Summary The ultrastructure of holocellulose and alpha-cellulose from Pinus radiata D. Don was examined after treatment with cellulase for either 24 hours or 7 days. A procedure for localising the enzyme in situ using phosphotungstic acid is described. The pattern of degradation differed between the two substrates with alpha-cellulose being much more susceptible to hydrolysis than holocellulose. In both substrates the primary wall showed evidence of hydrolysis after 24 hours and was completely hydrolysed after 7 days. In holocellulose after 7 days treatment, hydrolysis of the secondary wall was confined to localised areas of the S3 layer sometimes penetrating into the S2 region. In contrast, alpha-cellulose showed uniform degradation across the secondary wall. Enzyme did not appear to penetrate the holocellulose but full penetration occurred in alpha-cellulose, the enzyme being closely associated with individual microfibrils. The reasons for these differences in degradation pattern are discussed. 相似文献
14.
Summary The degradation of microfibrils from Valonia ventricosa by cellulase has been studied. As a result of enzymatic attack the elementary fibrils making up the microfibrils tended to separate and the ends of the microfibrils became oblique or pointed. The terminal planes made angles of 60 ... 66°, 33°, or 20 ... 25° with the microfibril axis. These planes are assumed to correspond to the 41
, 43
and 45
planes of the cellulose lattice and it is suggested that they are planes along which it is progressively more difficult for hydrolysis to proceed. On the basis of these considerations a suggestion has been proposed to explain the form of erosion cavities formed by soft-rot fungi described by previous workers in wood fibres and tracheids.
Zusammenfassung Der Cellulase-Abbau von Mikrofibrillen aus Valonia ventricosa wurde untersucht. Die enzymatische Wirkung führt dazu, daß die Elementarfibrillen, welche die Mikrofibrillen bilden, eine Tendenz zur Ablösung zeigen und daß die Enden der Mikrofibrillen schräg oder spitz zulaufen. Die Endflächen bilden mit der Mikrofibrillenachse Winkel von 60 ... 66°, 33° oder 20 ... 25°. Es wird angenommen, daß diese Flächen mit den Ebenen 41 , 43 and 45 des Cellulosegitters übereinstimmen und daß entlang dieser Ebenen die Hydrolyse zunehmend schwieriger wird. Aufgrund dieser Überlegungen wird eine Hypothese entwickelt, welche zur Erklärung der von den Moderfäulepilzen erzeugten, erosiven Vertiefungen dient, die bereits in verschiedenen Arbeiten über Holzfasern und Tracheiden beschrieben wurden.相似文献
15.
lntroductionAsaresuItofthepublic'sincreasingenvironmentalawareness,theresearchesfocusedondevelopingprocessesthatutilizeIowtoxicorganicsoIventshavefIourishedinthepast1oyears.Mostofthesere-searcheshaveexaminedthepossibilityofusingsu-percriticaIandslightIysubcriticalfluidsaseXtractionandreactionsolvents(Reaves1999).SupercriticalfIuidextractionoflignoceIluIosicma-teriaIsfrombiomassissimilartopyrolysis,whichisusedtoconvertbiomasstousefuIchemicalsorfluidfuels(Goto199o).ThepyroIysisofbiomasscan… 相似文献
16.
P. Sittisart M. M. Hyland M. A. Hodgson C. Nguyen A. Fernyhough 《Wood Science and Technology》2014,48(4):841-853
The aim of this project was to fabricate electroless nickel-coated cellulose fibres. Ultimately, these nickel-coated cellulose fibres will be used to develop a cost-effective polymer composite for electromagnetic interference (EMI) shielding and/or electrostatic discharge (ESD) applications. An attempt has been made to impart electrical conductivity onto cellulose fibres via an electroless nickel plating process. The aim was to achieve a homogeneous, continuous layer of Ni on the cellulose fibres, and the plating conditions were optimized to achieve this. The relationship between the coating morphology and the performance of the coated fibre was also of interest. Testing was carried out using cellulose filter paper and then loose cellulose fibres. Scanning electron microscopic (SEM) images of nickel-coated filter paper showed that nickel particles are bonded to the cellulose fibres. The coating appeared more compacted and continuous as plating time increased, corresponding to lower surface resistivity. This observation suggested a correlation between morphology and electrical conductivity of the coating. For nickel-coated cellulose fibres, after optimization of plating conditions, a uniform deposition of nickel particles around the cellulose surfaces was confirmed by SEM images. EDS and XRD results confirmed similar coating could be produced on filter paper and cellulose fibres. SEM images of cross-sectioned nickel-coated cellulose fibres illustrated nickel particles had penetrated into the inner walls of the cellulose fibres. This impregnation of the fibres should act to increase the bonding between nickel coating and cellulose fibres. These nickel-impregnated cellulose fibres could now be incorporated into a polymer matrix to create an electrically conducting composite with the right processing parameters. 相似文献
17.
We measured the longitudinal and tangential shrinking processes in wood specimens from Chamaecyparis obtuse Endl. with different microfibril angles (MFAs). The shape of the shrinking curve was compared with the MFA. Only the longitudinal
shrinking process of specimens with a small MFA clearly showed nonlinearity, and the degree of nonlinearity increased as the
MFA decreased. In contrast, the tangential shrinking process and the longitudinal shrinking process of compression wood with
a large MFA were linear. The nonlinearity is probably caused by the longitudinal shrinkage of the noncrystalline region of
the cellulose microfibril (CMF) in regions of low moisture content during water desorption. When the moisture content is high,
the matrix substance in the cell wall begins to dry; however, the shrinkage in the chain direction is restrained by the rigid
CMF. As the wood dries further, the noncrystalline region of the CMF embedded in the matrix substance begins to shrink. Because
the longitudinal mechanical behavior of wood with a small MFA is greatly affected by a rigid CMF, longitudinal shrinkage increases
suddenly at about 10% moisture content; as a result, the shrinking process shows nonlinearity. 相似文献
18.
Summary Sorption isotherms of ammonia were measured on cellulosic materials, such as beech and birch wood, as well as on cotton cellulose, the object being to obtain information on the nature of interaction between the wood and the ammonia by means of application of various sorption theories. As a result several analogies between the sorption of ammonia vapour and water vapour could be observed.—The isotherms displayed the typical S-shape and developed a hysteresis along the adsorption and desorption lines. The sorbate films reached a thickness of 4–6 molecular layers. The lowering of enthalpy of the ammonia vapour appeared to be the propelling force of the sorption process, as in the case with the uptake of water vapour.—In contrast to water isotherms, however, ammonia isotherms cannot be reproduced with the same specimen. Each sorption cycle brought a loss of substance and a reduction of the fibre saturation capacities of the adsorbent. In ammonia vapour the fibre saturation points were found at sorbate concentrations twice as high as in water vapour. The hysteresis between the adsorption and desorption processes also appeared with ammonia vapour; however, the continuous changes of the adsorbent, caused by chemical interaction with ammonia, produced heavy displacements. The specific surface area of the samples in ammonia was approximately twice the size of that in water, but the extensions varied greatly during the sorption cycles.These investigations have been supported by the Zentenarfonds of the Swiss Federal Institute of Technology. 相似文献
19.
Tamer Y. A. Fahmy Fardous Mobarak Yehia Fahmy M. H. Fadl M. El-Sakhawy 《Wood Science and Technology》2006,40(1):77-86
The present work shows for the first time worldwide that sucrose can be easily placed by simple techniques within the micropores
or nanostructure of the mercerized non-dried cotton linter fibers to create a low-cost cellulose substitute. Such sucrose-containing
nanocomposites find suitable use as specialty absorbent paper. Relative to the sucrose-free paper, the sucrose-containing
counterparts exhibit greater breaking length and remarkably high water uptake (WRV) up to a sucrose content of 8–15% w/w.
Mercerization of cotton linters before incorporating them with sucrose greatly enhanced the retention of sucrose in the prepared
paper nanocomposites as compared to the case of unmercerized cotton linters. We assume that regions of the cell wall lamellae,
on both sides of the sucrose spacers, are stressed during drying because the sucrose spacers hinder them to relax. This leads
to a strain, which makes some microfibrils partially released and protrude out of the fiber. Thus, a sort of fiber beating
takes place. We called this phenomenon incorporation beating or encapsulation beating to differentiate it from chemical and mechanical beatings, and it explains the great increase in breaking length of the paper
nanocomposites prepared from the mercerized non-dried sucrose-loaded linters.
This article is dedicated to Professor Dr. Dr. h.c. mult. Walter Liese on the occasion of his 80th birthday. 相似文献