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Amorphous Cellulose

The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform

Yun Yu – 1st expert 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 – 2nd expert 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 – 3rd expert 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, Dominique Derome, Sinan Keten, Sergey V Churakov, Jan Carmeliet

    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.