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Mohamed Naceur Belgacem - One of the best experts on this subject based on the ideXlab platform.

  • crab shell chitin whiskers reinforced natural rubber nanocomposites 3 effect of Chemical Modification of chitin whiskers
    Biomacromolecules, 2003
    Co-Authors: Kalaprasad Gopalan Nair, Alain Dufresne, Alessandro Gandini, Mohamed Naceur Belgacem
    Abstract:

    The purpose of this study was to Chemically modify the surface of chitin whiskers and to investigate the effect of the incorporation of these modified whiskers into a natural rubber (NR) matrix on the properties of the ensuing nanocomposite. Different Chemical coupling agents were tested, namely, phenyl isocyanate (PI), alkenyl succinic anhydride (ASA) (Accosize 18 from American Cyanamid), and 3-isopropenyl-alpha,alpha'-dimethylbenzyl isocyanate (TMI). The extent of Chemical Modification was evaluated by Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and surface energy analysis. After Chemical Modification, nanocomposite films were obtained using a toluene natural rubber solution in which the whiskers were dispersed. Their mechanical properties were found to be inferior to those of unmodified chitin/NR composites presented in our previous study. In fact, even though there is an increase in filler-matrix interaction as a result of Chemical Modification of the chitin whiskers, this does not contribute to the improvement in the mechanical properties of the resulting nanocomposite. It is concluded that this loss of performance is due to the partial destruction of the three-dimensional network of chitin whiskers assumed to be present in the unmodified composites.

Shaoming Huang - One of the best experts on this subject based on the ideXlab platform.

  • plasma activation of carbon nanotubes for Chemical Modification
    Journal of Physical Chemistry B, 2001
    Co-Authors: Qidao Chen, Shaoming Huang
    Abstract:

    A novel approach for Chemical Modification of carbon nanotubes was developed, which involved radio frequency glow-discharge plasma activation, followed by Chemical reactions characteristic of the plasma-generated functional groups. For instance, amino-dextran chains have been immobilized onto acetaldehyde-plasma-treated aligned carbon nanotubes through the formation of Schiff-base linkages, which were further stabilized by reduction with sodium cyanoborohydride. Using the same reaction, we have also Chemically grafted periodate-oxidized dextran chains pre-labeled with fluorescein onto ethylenediamine-plasma-treated carbon nanotubes. The fluorescein labeling allows the surface immobilization reaction to be followed simply by photoluminescence measurements. The resulting polysaccharide-grafted carbon nanotubes are very hydrophilic, as demonstrated by X-ray photoelectron spectroscopic and air/water contact angle measurements.

Kalaprasad Gopalan Nair - One of the best experts on this subject based on the ideXlab platform.

  • crab shell chitin whiskers reinforced natural rubber nanocomposites 3 effect of Chemical Modification of chitin whiskers
    Biomacromolecules, 2003
    Co-Authors: Kalaprasad Gopalan Nair, Alain Dufresne, Alessandro Gandini, Mohamed Naceur Belgacem
    Abstract:

    The purpose of this study was to Chemically modify the surface of chitin whiskers and to investigate the effect of the incorporation of these modified whiskers into a natural rubber (NR) matrix on the properties of the ensuing nanocomposite. Different Chemical coupling agents were tested, namely, phenyl isocyanate (PI), alkenyl succinic anhydride (ASA) (Accosize 18 from American Cyanamid), and 3-isopropenyl-alpha,alpha'-dimethylbenzyl isocyanate (TMI). The extent of Chemical Modification was evaluated by Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and surface energy analysis. After Chemical Modification, nanocomposite films were obtained using a toluene natural rubber solution in which the whiskers were dispersed. Their mechanical properties were found to be inferior to those of unmodified chitin/NR composites presented in our previous study. In fact, even though there is an increase in filler-matrix interaction as a result of Chemical Modification of the chitin whiskers, this does not contribute to the improvement in the mechanical properties of the resulting nanocomposite. It is concluded that this loss of performance is due to the partial destruction of the three-dimensional network of chitin whiskers assumed to be present in the unmodified composites.

Luke Hanley - One of the best experts on this subject based on the ideXlab platform.

  • Chemical Modification of polystyrene surfaces by low energy polyatomic ion beams
    Journal of Physical Chemistry B, 1998
    Co-Authors: Earl T Ada, Oleg Kornienko, Luke Hanley
    Abstract:

    The Chemical Modification of polystyrene surfaces by low-energy (10−100 eV) SF5+, C3F5+, and SO3+ ions was studied by X-ray photoelectron spectroscopy and two-laser ion trap mass spectrometry. The mechanism of fluorination was found to be dissimilar for SF5+ and C3F5+ ions in this energy range at fluences of 1014−1016 ions/cm2. SF5+ was found to induce fluorination of the polymer surface by grafting reactive F atoms upon dissociation at impact. SFn fragments were not found to be grafted or implanted into the polymer. Sulfur was detected on the polymer surface only at incident energies above 50 eV and was found to be sulfidic in nature. In contrast, C3F5+ ions induced grafting of both reactive F atoms and molecular CmFn fragments from the dissociation of the incident projectile. Larger proportions of highly fluorinated sites and thicker fluorocarbon layers were found for C3F5+ at all energies and fluences. A variety of aliphatic and aromatic fluorine bonding environments were detected on both SF5+ and C3F5...

Roberto Fernandezlafuente - One of the best experts on this subject based on the ideXlab platform.

  • Chemical Modification in the design of immobilized enzyme biocatalysts drawbacks and opportunities
    Chemical Record, 2016
    Co-Authors: Nazzoly Rueda, Jose Dos C S Santos, Claudia Ortiz, Rodrigo Torres, Oveimar Barbosa, Rafael C Rodrigues, Angel Berenguermurcia, Roberto Fernandezlafuente
    Abstract:

    Chemical Modification of enzymes and immobilization used to be considered as separate ways to improve enzyme properties. This review shows how the coupled use of both tools may greatly improve the final biocatalyst performance. Chemical Modification of a previously immobilized enzyme is far simpler and easier to control than the Modification of the free enzyme. Moreover, if protein Modification is performed to improve its immobilization (enriching the enzyme in reactive groups), the final features of the immobilized enzyme may be greatly improved. Chemical Modification may be directed to improve enzyme stability, but also to improve selectivity, specificity, activity, and even cell penetrability. Coupling of immobilization and Chemical Modification with site-directed mutagenesis is a powerful instrument to obtain fully controlled Modification. Some new ideas such as photoreceptive enzyme modifiers that change their physical properties under UV exposition are discussed.

  • coupling Chemical Modification and immobilization to improve the catalytic performance of enzymes
    Advanced Synthesis & Catalysis, 2011
    Co-Authors: Rafael C Rodrigues, Angel Berenguermurcia, Roberto Fernandezlafuente
    Abstract:

    Chemical Modification and immobilization of enzymes have been usually considered unrelated tools to improve biocatalyst features. However, there are many examples where a Chemically modified enzyme is finally used in an immobilized form, and that exemplifies how both tools may be complementary resulting in a synergism in the final results. In this review we present some of the strategies that may give that result. For example, the Chemical Modification of soluble enzymes may be used to improve their immobilization (reinforcing adsorption or improving multipoint covalent attachment), or just to improve enzyme stability and facilitate the selection of the immobilization conditions. Chemical Modification of previously immobilized enzymes benefits from solid-phase chemistry due to the nature of enzymes (e.g., prevention of inactivation, aggregation, etc.). The use of different targets for Chemical Modifications with small molecules or multifunctional polymers are also discussed: intramolecular or intersubunit cross-linking, one-point Modification, generation of artificial microenvironments, etc.