Dielectric spectroscopic results and chemical accessibility of sulfite pulps

Einfeldt, J.; Kwasniewski, Albert; Meißner, Dana; Gruber, E.; Henricks, R.

doi:10.1002/1439-2054(20001101)283:1<7::aid-mame7>3.3.co;2-z

Cited by 5 publications

(10 citation statements)

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“…These two relaxation modes have been resolved experimentally in a series of elementary thermograms revealing the existence of a discrete distribution of relaxation times. According to the literature, the c relaxation mode of cellulose has been attributed to molecular mobility of Roig et al 2011a) and the b relaxation mode of cellulose to molecular mobility of glycosidic rings thanks to b 1-4 glycosidic bonds (Saad et al 1996;Saad and Furuhata 1997;Einfeldt et al 2000aEinfeldt et al , b, 2001Einfeldt et al , 2003Einfeldt et al , 2004Einfeldt and Kwasniewski 2002;Meissner et al 2000;Jafarpour et al 2007Jafarpour et al , 2009). Lignin has also been studied by TSC in the low temperature range.…”

Section: Resultsmentioning

confidence: 99%

Dielectric and mechanical properties of various species of Madagascan woods

et al. 2017

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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. Any correspondence concerning this service should be sent to the repository administrator: staff-oatao@listes-diff.inp-toulouse.fr Abstract The low-temperature molecular mobility of three different wood species was analyzed, with the two major constituents-cellulose and lignin-as reference. Mechanical and dielectric dynamic techniques were used. In order to observe the fine structure of the broad relaxation modes of wood, a very low-frequency analysis was carried out by thermostimulated current technique. Low-temperature relaxations of rosewood were assigned to low-temperature relaxations of cellulose. There was no dielectric response of lignin in rosewood. Contrarily, both cellulose and lignin responses were distinguished in ebony and varongy. Thermostimulated currents analyses exhibit the specific behavior of lignin in the various wood species. Moreover, the relaxation mode of cellulose observed at lower temperature remains localized in rosewood, while it tends to delocalize in varongy and ebony. The nature and intensity of physical interactions that induce variation of phase miscibility might be responsible for the observed differences. Even at the scale of the c relaxation, physical interactions modify molecular mobility.

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Section: Resultsmentioning

confidence: 99%

Dielectric and mechanical properties of various species of Madagascan woods

et al. 2017

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“…The activation energy of the γ mode increases with the hydration level whereas it decreases for the β mode. The increase of the activation energy indicates the decrease of its molecular mobility [23,28,53]. The hydroxyl and hydroxymethyl groups form water-polymer complexes.…”

Section: Isothermal Dynamic Dielectric Responsementioning

confidence: 99%

“…Dielectric dynamic spectroscopy (DDS) has been already used on polysaccharides like cellulose and its derivatives [22][23][24][25][26][27][28][29]. Four dielectric relaxations modes are usually observed γ, β, β wet and α, in the order of increasing temperatures [22][23][24][25][26][27][28][29].…”

Section: Introductionmentioning

confidence: 96%

“…Four dielectric relaxations modes are usually observed γ, β, β wet and α, in the order of increasing temperatures [22][23][24][25][26][27][28][29]. The dielectric properties of cellulose have been also investigated by combined DDS/TSC [28].…”

Section: Introductionmentioning

confidence: 99%

“…A β wet relaxation mode can be observed in all wet polysaccharides in the room temperature range (0-60°C) [22][23][24][25][26][27]. This mode is not observed anymore after drying the sample [22][23][24][25][26][27]. The hydration influence of polysaccharides on their dielectric properties can be interpreted by several hypotheses: one the one hand, the OH-groups of glucosidic units form hydrogen bonds with water molecules.…”

Section: Introductionmentioning

confidence: 99%

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Influence of hydrogen bonds on glass transition and dielectric relaxations of cellulose

Roig¹,

Dantras²,

Dandurand³

et al. 2011

J. Phys. D: Appl. Phys.

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The molecular dynamic in hydrated cellulose has been investigated by a combination of thermal analyses and dielectric spectroscopy. Differential Scanning Calorimetry (DSC) shows the dependence upon hydration of the glass transition temperature T g . A physical ageing phenomenon has been observed. At the molecular scale, bound water is hydrogen bonded to polar sites of cellulose macromolecules. At the macroscopic scale, water molecules play the role of a plasticizer for cellulose lowering its T g . Dynamic Dielectric Spectroscopy (DDS) combined with Thermostimulated Currents (TSC) have allowed us to follow more localized molecular mobility. The β relaxation mode is characterized by activation entropies that vanish for higher water contents indicating molecular mobility localization. It is plasticized by water like the glass transition. This analogy is explained by a common origin of both mechanisms: the mobility of the cellulose backbone. The evolution of the γ mode upon hydration follows an anti-compensation law. Water acts as an anti-plasticizer in a hydrogen bonded network.

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Comparison of the molecular dynamics of celluloses and related polysaccharides in wet and dried states by means of dielectric spectroscopy

Einfeldt¹,

Meißner

Kwasniewski

2000

Macromol. Chem. Phys.

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The dielectric relaxation spectra of polysaccharides are already affected very specifically by small amounts of water. The measured samples of cellulose, starch and dextran behave differently in the wet and in the dried state comparing their low temperature dielectric spectra: The positions of the secondary relaxation in the frequency scale, which are due to the local chain mobility, shift in a specific manner between wet and dried state for every substance. In general, we can say that drying strongly decreases the relaxation strength for all samples. The dielectric spectra of the wet polysaccharides (2 to 12% w/w water content) show an additional relaxation process (βwet‐relaxation) in the room temperature range (0°C to 60°C) which vanishes after an intensive drying procedure. The experimental results were fitted by using the Havriliak‐Negami‐equation for each individual relaxation process. This evaluation leads to a number of physical parameters for the polymer dynamics given in the paper. The results could be explained by the differences in the interaction of the several polysaccharides with water caused by their distinct glycosidic linked backbones and their different supramolecular structures.

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Dielectric spectroscopic results and chemical accessibility of sulfite pulps

Cited by 5 publications

References 0 publications

Dielectric and mechanical properties of various species of Madagascan woods

Dielectric and mechanical properties of various species of Madagascan woods

Influence of hydrogen bonds on glass transition and dielectric relaxations of cellulose

Comparison of the molecular dynamics of celluloses and related polysaccharides in wet and dried states by means of dielectric spectroscopy

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