Amorphous Cellulose

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Yun Yu - One of the best experts on this subject based on the ideXlab platform.

  • in situ structural changes of crystalline and Amorphous Cellulose during slow pyrolysis at low temperatures
    Fuel, 2018
    Co-Authors: Erwei Leng, Yang Zhang, Yang Peng, Xun Gong, Xiaomin Li, Yun Yu
    Abstract:

    Abstract This study reveals the evolution of functional groups during slow pyrolysis of crystalline and Amorphous Cellulose at low temperatures, using in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy combined with two-dimensional perturbation correlation infrared spectroscopy (2D-PCIS). During Cellulose pyrolysis, although the inter-molecular hydrogen bonds are slightly stronger, both intra- and inter-molecular hydrogen bonds can break at low temperatures (i.e., >120 °C), leading to the formation of free hydroxyl. Due to the weakened hydrogen bonds in Cellulose, dehydration reactions firstly take place to produce saturated carbonyls, at a lower temperature (i.e., 240 °C) for Amorphous Cellulose. At increased temperatures (i.e., >270 °C), the hydrogen bonds in Cellulose reduce more significantly, promoting the decomposition of glucopyranose rings to form double bonds (i.e., carbonyls, carboxyls and conjugated alkenes). Compared to those for Amorphous Cellulose, the hydrogen bonds in crystalline Cellulose are more stable, thus protecting the functional groups (i.e., CH groups, glycosidic bonds and glucopyranose rings) from rapid disruption.

  • evolution of water soluble and water insoluble portions in the solid products from fast pyrolysis of Amorphous Cellulose
    Industrial & Engineering Chemistry Research, 2013
    Co-Authors: Yun Yu, Hongwei Wu
    Abstract:

    The formation of water-soluble intermediates is an important phenomenon during Cellulose pyrolysis. This study investigates the evolution of the water-soluble and water-insoluble portions in the solid products during the pyrolysis of an Amorphous Cellulose sample, which is known to generate substantial amounts of water-soluble intermediates at low temperatures (250 and 300 °C). The yield of the water-soluble portion initially increases to a maximum up to ∼30% (on a carbon basis), depending on the pyrolysis conditions used in this study. Further pyrolysis reactions lead to a decrease in the yield of the water-soluble portion. In contrast, the yield of the water-insoluble portion initially decreases rapidly as pyrolysis proceeds and then starts to level off. Such leveling-off behavior of the water-insoluble portion indicates that at least part of the water-soluble portion is converted into the water-insoluble portion through repolymerization. An increase in temperature promotes the formation of the water-so...

  • differences in water soluble intermediates from slow pyrolysis of Amorphous and crystalline Cellulose
    Energy & Fuels, 2013
    Co-Authors: Yun Yu, Hongwei Wu
    Abstract:

    The paper reports the significant differences in the pyrolysis behavior between Amorphous and crystalline Cellulose. The strong hydrogen bonding networks in crystalline Cellulose appear to preserve the sugar ring structure during pyrolysis so that the yield (a maximum of ∼30% on a carbon basis at 250 °C) of water-soluble intermediates for Amorphous Cellulose is considerably higher than that (a maximum of ∼3% on a carbon basis at 270 °C) of crystalline Cellulose pyrolysis. Direct evidence was also provided to prove that various sugar oligomers (DPs: 1–14) present in water-soluble intermediates are indeed produced from some short glucose chain segments in Amorphous Cellulose during pyrolysis at a temperature as low as 140 °C. The weak hydrogen bonding networks in Amorphous Cellulose allow the liberation of these short glucose chain segments as pyrolysis intermediates. Compared to those from crystalline Cellulose, the water-soluble intermediates from Amorphous Cellulose contain considerably more sugar oligom...

Hongwei Wu - One of the best experts on this subject based on the ideXlab platform.

  • evolution of water soluble and water insoluble portions in the solid products from fast pyrolysis of Amorphous Cellulose
    Industrial & Engineering Chemistry Research, 2013
    Co-Authors: Yun Yu, Hongwei Wu
    Abstract:

    The formation of water-soluble intermediates is an important phenomenon during Cellulose pyrolysis. This study investigates the evolution of the water-soluble and water-insoluble portions in the solid products during the pyrolysis of an Amorphous Cellulose sample, which is known to generate substantial amounts of water-soluble intermediates at low temperatures (250 and 300 °C). The yield of the water-soluble portion initially increases to a maximum up to ∼30% (on a carbon basis), depending on the pyrolysis conditions used in this study. Further pyrolysis reactions lead to a decrease in the yield of the water-soluble portion. In contrast, the yield of the water-insoluble portion initially decreases rapidly as pyrolysis proceeds and then starts to level off. Such leveling-off behavior of the water-insoluble portion indicates that at least part of the water-soluble portion is converted into the water-insoluble portion through repolymerization. An increase in temperature promotes the formation of the water-so...

  • differences in water soluble intermediates from slow pyrolysis of Amorphous and crystalline Cellulose
    Energy & Fuels, 2013
    Co-Authors: Yun Yu, Hongwei Wu
    Abstract:

    The paper reports the significant differences in the pyrolysis behavior between Amorphous and crystalline Cellulose. The strong hydrogen bonding networks in crystalline Cellulose appear to preserve the sugar ring structure during pyrolysis so that the yield (a maximum of ∼30% on a carbon basis at 250 °C) of water-soluble intermediates for Amorphous Cellulose is considerably higher than that (a maximum of ∼3% on a carbon basis at 270 °C) of crystalline Cellulose pyrolysis. Direct evidence was also provided to prove that various sugar oligomers (DPs: 1–14) present in water-soluble intermediates are indeed produced from some short glucose chain segments in Amorphous Cellulose during pyrolysis at a temperature as low as 140 °C. The weak hydrogen bonding networks in Amorphous Cellulose allow the liberation of these short glucose chain segments as pyrolysis intermediates. Compared to those from crystalline Cellulose, the water-soluble intermediates from Amorphous Cellulose contain considerably more sugar oligom...

Jan Carmeliet - One of the best experts on this subject based on the ideXlab platform.

  • molecular mechanism of moisture induced transition in Amorphous Cellulose
    ACS Macro Letters, 2014
    Co-Authors: Karol Kulasinski, Sinan Keten, Sergey V Churakov, R A Guyer, Jan Carmeliet, Dominique Derome
    Abstract:

    We investigate the influence of adsorbed water on Amorphous Cellulose structure and properties, within the full range of moisture content from the dry state to saturation, by molecular dynamics simulation. Increasing water content results in overall swelling, a substantial decrease in stiffness, and higher diffusivity of the water molecules. The obtained sorption curve as well as the range of swelling and weakening are confirmed by experiments. The measured properties undergo a noticeable change at about 10% of moisture content, which suggests that a transition occurs in the porous system, indicating that the sorption process is stepwise. Our analysis of water network formation reveals that the onset of percolation coincides with the moisture content at which a transition in the material properties is observed. An in-depth analysis of the molecular mechanism of hydrogen bonding, van der Waals interactions, and water network in the two regimes enhances the understanding of the adsorption process.

  • a comparative molecular dynamics study of crystalline paracrystalline and Amorphous states of Cellulose
    Cellulose, 2014
    Co-Authors: Karol Kulasinski, Sinan Keten, Sergey V Churakov, Jan Carmeliet, Dominique Derome
    Abstract:

    The quintessential form of Cellulose in wood consists of microfibrils that have high aspect ratio crystalline domains embedded within an Amorphous Cellulose domain. In this study, we apply united-atom molecular dynamics simulations to quantify changes in different morphologies of Cellulose. We compare the structure of crystalline Cellulose with paracrystalline and Amorphous phases that are both obtained by high temperature equilibration followed by quenching at room temperature. Our study reveals that the paracrystalline phase may be an intermediate, kinetically arrested phase formed upon amorphisation of crystalline Cellulose. The quenched structures yield isotropic Amorphous polymer domains consistent with experimental results, thereby validating a new computational protocol for achieving Amorphous Cellulose structure. The non-crystalline Cellulose compared to crystalline structure is characterized by a dramatic decrease in elastic modulus, thermal expansion coefficient, bond energies, and number of hydrogen bonds. Analysis of the lattice parameters shows that Iβ Cellulose undergoes a phase transition into high-temperature phase in the range of 450–550 K. The mechanisms of the phase transition elucidated here present an atomistic view of the temperature dependent dynamic structure and mechanical properties of Cellulose. The paracrystalline state of Cellulose exhibits intermediate mechanical properties, between crystalline and Amorphous phases, that can be assigned to the physical properties of the interphase regions between crystalline and Amorphous Cellulose in wood microfibrils. Our results suggest an atomistic structural view of Amorphous Cellulose which is consistent with experimental data available up to date and provide a basis for future multi-scale models for wood microfibrils and all-Cellulose nanocomposites.

J Y Cavaille - One of the best experts on this subject based on the ideXlab platform.

  • secondary dielectric relaxations in dried Amorphous Cellulose and dextran
    Polymer, 1999
    Co-Authors: H Montes, J Y Cavaille
    Abstract:

    Abstract Cellulose and dextran are biosynthesized polysaccharides, made of glucose repeat units linked together by (β 1→4) and (α 1→6) linkages, respectively. Furthermore, Cellulose has two hydroxyl groups and one hydroxymethyl group per glucose ring, while dextran has three hydroxyl groups and no hydroxymethyl group. This work deals with the characterization of dielectric secondary relaxations of Amorphous dextran and Cellulose. Dextran exhibits two dielectric secondary relaxations referred to as γddex and βddex, while Cellulose has only one very broad relaxation, γdcell. The γddex relaxation process has an average activation energy and a pre-exponential time τo of 32 kJ mol−1 and 5×10−15 s respectively. This weakly cooperative relaxation process should be associated with the rotation of hydroxyl groups. The βddex relaxation has an average activation energy and a pre-exponential time τo of 82 kJ mol−1 and 10−20 s respectively. This activation energy has both enthalpic and entropic contributions. The comparison with mechanical relaxation data indicates that βddex results mainly from the motions of main chain segments. The analysis of the two dielectric relaxations of dextran leads to the conclusion that γdcell could result from the overlap of two processes corresponding respectively to the rotation of hydroxyl groups and to the rotation of hydroxymethyl groups.

  • the mechanical β relaxation in Amorphous Cellulose
    Journal of Non-crystalline Solids, 1998
    Co-Authors: H Montes, Karim Mazeau, J Y Cavaille
    Abstract:

    Abstract Amorphous Cellulose exhibits two secondary relaxations, so-called γcell and βcell, at temperatures below its glass transition temperature. The activation energy of γcell indicates that it corresponds to noncooperative motions and the comparison with other polysaccharides leads to the conclusion that it corresponds to the rotation of CH2OH lateral groups. This proposal has been confirmed by preliminary molecular modeling. On the contrary, experimental data indicates that the activation energy of the βcell has an entropic contribution which leads to the conclusion that molecular motions at its origin should be cooperative. Preliminary molecular modeling calculations performed on isolated chains in vacuum with random conformations, indicate conformational changes can occur between equivalent energy conformers. Such hopping jumps seem to involve a limited number of repeat units (about six according to these results).

  • secondary mechanical relaxations in Amorphous Cellulose
    Macromolecules, 1997
    Co-Authors: H Montes, Karim Mazeau, J Y Cavaille
    Abstract:

    Amorphous Cellulose exhibits two mechanical relaxation processes, so-called γ and β, below its glass transition temperature Tg. Though much work has already been published on the subject, the origin of these relaxations is still uncertain, especially because most of the dynamic mechanical data were obtained at constant frequency and mixed together with dielectric data. In order to reach more definitive answers, two main approaches were taken in this work, namely (i) the use of a low-frequency mechanical spectroscopic technique and (ii) the comparison with data of different polysaccharides, having different lateral groups and different intramolecular links along the main chain. In addition, preliminary molecular modeling based on molecular mechanics was performed on isolated chains in vacuum. The work is focused on dried Cellulose, to minimize the effect of relaxation overlap, which becomes negligible for moisture content lower than 2%. The results show that the γ process occurs without cooperativity and c...

  • secondary relaxations in Amorphous Cellulose
    Journal of Non-crystalline Solids, 1994
    Co-Authors: H Montes, J Y Cavaille, Karim Mazeau
    Abstract:

    Abstract Dynamic mechanical analysis of Amorphous Cellulose allows observation of two secondary relaxation processes γ and β, and characterization of them by their activation energies and pre-exponential times (in an Arrhenius approximation). In order to find a molecular interpretation of these processes, different experiments and theoretical approaches have been used. Mechanical spectrometry experiments were performed on Cellulose and other polysaccharides (dextran and pullulan). All of these data lead to hypotheses about the origins of the relaxation processes. Molecular modelling calculations were used to confirm and complete them.

John Ralph - One of the best experts on this subject based on the ideXlab platform.

  • a gel state 2d nmr method for plant cell wall profiling and analysis a model study with the Amorphous Cellulose and xylan from ball milled cotton linters
    RSC Advances, 2014
    Co-Authors: John Ralph
    Abstract:

    A recently developed “gel-state NMR method” that simply swells plant cell walls in a DMSO-d6/pyridine-d5 (4 : 1) solvent system and uses a high-resolution solution state 2D-NMR (HSQC) technique has been successfully applied to whole plant cell wall 2D-NMR profiling studies. However, there was limited information to assign many polysaccharide peaks unlike lignin structures. Here we collected NMR data from various Cellulose and xylan models using the same solvent system to assign the unknown peaks. Furthermore, DMSO-soluble Cellulose and xylan fractions were prepared from ball-milled cotton linter Cellulose, and the detailed chemical structures were analyzed. The major component of cotton is Cellulose (95–99%), but it typically contains ∼2% hemiCelluloses. Xylan in particular was isolated and identified along with the Amorphous Cellulose in this study. The fully assigned spectra of Cellulose and xylan provided invaluable database information for peak assignment and authentication that will be directly used to screen and identify the two main polysaccharide components from various whole cell wall NMR spectra in the same solvent system.