Lichtmikroskopische und übermikroskopische Untersuchungen an natürlichen und künstlichen Cellulosefasern

Eisenhut, O.; Kuhn, E.

doi:10.1002/ange.19420552503

Cited by 36 publications

(8 citation statements)

References 6 publications

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“…Following the development of the first commercially available transmission electron microscope by E. Ruska (Von Borries and Ruska, 1939;Ruska, 1987), cellulose scientists saw the opportunity to directly visualize the fine structure of cellulose fibers at a resolution much higher than that of the optical microscopes. Despite this potential, the first micrographs of cellulose were somewhat deceptive, lacking sufficient contrast to reveal the fine details of the fibrillar specimens, since only the thickest parts of the samples could be visualized (Ruska, 1940;Ruska and Kretschmer, 1940;Eisenhut andKuhn, 1942, Husemann andCarnap, 1943a;Husemann and Carnap, 1943b;Ruska, 1944;Frey-Wyssling and Mühlethaler, 1946). This lack of contrast was partly due to the electron transparency of cellulose that is constituted of light atoms, but also to the use of too intense electron beams that damaged the samples (Hamann, 1942).…”

Section: From Early X-ray Data To the First Electron Micrographs Of Cellulosementioning

confidence: 99%

Transmission electron microscopy of cellulose. Part 1: historical perspective

2018

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Following the first electron micrographs of cotton in 1940, the development of transmission electron microscopy applied to native cellulose has been evolving in a series of successive advances. At first, faced with the weak contrast of the early images, the operators had to use specific electron dense contrasting agents to reveal the ultrastructure of their samples.It was thus found that all native celluloses consisted of microfibrils, with some size variations depending on the sample origin. Following this, a major advance was achieved when the electron microscopes could be adjusted with low electron doses, allowing the recording of diffraction diagrams from the electron beam-sensitive cellulose samples. Under these conditions, one could obtain information of cellulose itself and not, as before, of the contrasting agent. This important development applied to microdiffraction conditions revealed that some large cellulose microfibrils could yield spot diagrams typical of single crystals. Their recording led to a decisive progress for resolving the molecular and crystal structure of the two cellulose allomorphs, cellulose Ia and Ib. Using various combinations of diffracted beams to create the images, the so called "diffraction contrast images" could then be developed. These micrographs showed many aspects of the crystalline core of cellulose, including spectacular high-resolution images showing the molecular planes of cellulose in their crystalline environment. Today, electron diffraction, diffraction contrast imaging and low-dose electron microscopy have become major tools to follow the effect of various physical, chemical and biochemical processes at the cellulose crystalline level.

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Section: From Early X-ray Data To the First Electron Micrographs Of Cellulosementioning

confidence: 99%

Transmission electron microscopy of cellulose. Part 1: historical perspective

2018

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“…During the following two decades, the progress in TEM imaging of cellulose was mostly driven by the motivation to characterize the submicrometer structure of natural cellulose fibers. However, the identification of smaller constituting elements required the disintegration of cell walls and fibers using strong mechanical and/or chemical treatment [26,[64][65][66][67][68]. In particular, images of individual crystalline "fragments" (not yet called CNCs) were recorded after strong sulfuric acid hydrolysis of celluloses from various sources [9,10,69,70].…”

Section: Selected Milestones In the Characterization Of Nanocellulosementioning

confidence: 99%

Transmission Electron Microscopy for the Characterization of Cellulose Nanocrystals

Kaushik¹,

Fraschini²,

Chauve³

et al. 2015

The Transmission Electron Microscope - Theory and Applications

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Cellulose nanocrystals CNCs are high aspect ratio nanomaterials readily obtained from cellulose microfibrils via strong acid hydrolysis. They feature unique properties stemming from their surface chemistry, their crystallinity, and their three-dimensional structure. CNCs have been exploited in a number of applications such as optically active coatings, nanocomposite materials, or aerogels. CNC size and shape determination is an important challenge and transmission electron microscopy TEM is one of the most powerful tools to achieve this goal. "ecause of the specifics of TEM imaging, CNCs require special attention. They have a low density, are highly susceptible to electron beam damage, and easily aggregate.Specific techniques for both imaging and sampling have been developed over the past decades. In this review, we describe the CNCs, their properties, their applications, and the need for a precise characterization of their morphology and size distribution. We also describe in detail the techniques used to record quality images of CNCs. Finally, we survey the literature to provide readers with specific examples of TEM images of CNCs.Keywords: cellulose nanocrystals, transmission electron microscopy, particle size, characterization, size distribution, sample preparation © 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. . Introduction . . Native cellulose and the production of cellulose nanocrystalsCellulose, the most abundant biopolymer on Earth, has been extensively used by man, in the form of macro-and microstructures, as a traditional resource in many aspects of daily life, notably to produce textiles and papers. This polymeric material is biosynthesized by a wide variety of living species such as plants, animals, bacteria, and some amoebas. Glucose is polymerized by enzymes in a continuous fashion. The resulting cellulose chains are homopolymers of β-, -linked anhydro-D-glucose units which associate to form microfibrils, further assembled into macrofibers and fibers. Crystalline and disordered regions alternate along the microfibrils Figure a [ -]. In the late s, cellulose crystallites were isolated for the first time by chemical treatment of a cotton substrate in hot concentrated sulfuric acid [ ]. Soon after, Rånby showed that stable colloidal suspensions of negatively charged cellulose particles could be obtained [ , ]. DuringThe Transmission Electron Microscope -Theory and Applications 130 the extraction process, the cellulosic fibrous structure is broken down in the presence of concentrated sulfuric acid other mineral acids can be used such as HCl . "fter diffusion of the acid within the substrate, the glycosidic linkages in disordered regions, more accessible and reactive, are preferentially broken. "n additional mechanical or ultrasound treatment resul...

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“…dropped off rapidly to a value of 150-200 and then slowly decreased with time. Since these results were published, others [ 1,2,3,6,8,13,14,19,20,21,23,25,27] have found similar results for the acid degradation-a rapid drop in D.P. followed by a much slower decrease at D.P.…”

Section: Introductionmentioning

confidence: 65%

“…The rate equation for the hydrolysis of cellulose was first derived by Freudenberg, Kuhn, and coworkers [6,7,8,9] and later by af Ekenstam [4,5 ] , Stamm and Cohen [24], Schulz and L6hmann [22], Battista [ 1 ] , Steele and Pacsu [25], and J §rgensen [ 14] . It was assumed that the degradation of the cellulose chains was a first-order unimolecular reac-tion, in which case the expression where c is the concentration of bonds capable of being hydrolyzed, t is the time of degradation, and k is the hydrolysis constant, is valid.…”

Section: Introductionmentioning

confidence: 99%