Browsing by Author "Parker, IH"

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    Hydration of paper studied with solid-state magnetisation-exchange H-1 NMR spectroscopy
    (Walter de Gruyter, 2006-07) Garvey, CJ; Parker, IH; Simon, GP; Whittaker, AK
    The wide-line H-1 nuclear magnetic resonance (NMR) spectrum of paper in equilibrium with ambient humidity consists of super-imposed relatively broad and narrow lines. The narrower line is of the order of 2 kHz wide at half the maximum height, while the broader line is of the order of 40 kHz in width at half height. On the basis of these line widths, the narrow line is assigned to water sorbed to the paper, and the broad line to the polymeric constituents of the paper. It was not possible to distinguish between the various polymeric components of paper contributing to the H-1 NMR spectra. A modified Goldman-Shen pulse sequence was used to generate a spatial magnetisation gradient between the polymer and water phases. The exchange of magnetisation between protons associated with water and those associated with the macromolecules in paper was observed. The exchange of magnetisation is discussed within a heat transfer model for homonuclear dipolar coupling, with exchange being characterised by a spin-diffusion coefficient. Consideration of the magnitude of the initial rate of the exchange process and estimates of the spin-spin relaxation times based on H-1 line widths indicate that some water must exist in a sufficiently immobile state as to allow homonuclear dipolar interactions between adjacent polymer and water protons. Thus, water sorbed onto paper must exist in at least two states in mass exchange with each other. This observation allows certain conclusions to be drawn about the ratio of free/bound water as a function of moisture content and the dispersal of water within the polymer matrix. © 2006, Walter de Gruyter
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    On the interpretation of x-ray diffraction powder patterns in terms of the nanostructure of cellulose I fibres.
    (Wiley-VCH Verlag Berlin, 2005-08-05) Garvey, CJ; Parker, IH; Simon, GP
    The average lateral dimensions of cellulose microfibrils in paper sheets can be determined from the width of X-ray Bragg peaks at half the maximum height. The method assumes it is the finite size of the crystallite which is the main contributor to peak broadening in the directions orthogonal to the long axis of the crystallite. The assumption is examined in the context of samples from different botanical sources, of varying crystallinity and cellulose content and the various instrumental sources of broadening X-ray powder patterns. Excellent fits to the data from paper samples can be obtained by using five Voigt functions to the powder diffraction patterns, for the 01, 101, 021, 002 and 040 reflections. Of these reflections, the 020 is the clearest, and the best able to determine the lateral dimension of the crystallite. Results indicate that the size of microfibrils is dependent on the botanical source of the fibres. © 2005, Wiley-VCH Verlag Berlin
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    Polymer nanoscale morphology in Chara australis Brown cell walls studied by advanced solid state techniques
    (National Museum of Natural History, 2006-11) Garvey, CJ; Keckes, J; Parker, IH; Beilby, M; Lee, GSH
    The cell wall of the green algae Chara australis Brown (Charophyta, Algae) has been examined with solid state techniques (suitable for characterising the nanoscale arrangement of polymers) and solid state chemistry. The chemical composition of a bulk dried sample of Chara australis was examined using cross-polarisation magic angle spinning (CP-MAS) C-13 nuclear magnetic resonance (NMR). The presence of phenyl-propane subunits typical of the cross linked polymer, lignin, is not revealed. The arrangement of cellulose in the cell wall was probed by examining the wide angle diffraction pattern of a single fibre oriented with respect to an x-ray beam. The pattern produced was typical of a textured crystalline lattice embedded in an amorphous matrix. The x-ray reflections are much broader than most found in higher plants and it is difficult to resolve texture. Polarised Raman scattering from a similar sample provided clearer evidence of a textured cellulose matrix embedded in an amorphous matrix. It is found that the charophyte cell wall has many similarities in chemical composition and nanoscale arrangement of cell wall polymers to that of the higher plant, including the presence and arrangement, of cellulose and various polysaccharides. © 2006, Elsevier Ltd.
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    Small angle scattering in the Porod region from hydrated paper sheets at varying humidities
    (Walter de Gruyter, 2004-08) Garvey, CJ; Parker, IH; Knott, RB; Simon, GP
    The microscopic changes in the structure of paper at different equilibrium moisture contents were examined using the novel technique of contrast variation small angle neutron scattering (SANS). Contrast variation, by appropriate selection of the H2O:D2O ratio, was used to simplify the scattering from hydrated paper to a twophase approximation. The two phases were paper polymers (cellulose, lignin and hemicelluloses) and a phase consisting of water and voids. The twophase approximation is justified by consideration of the chemistry and density of each of the polymer species belonging to paper, and by matching the scattering length density of the sorbed moisture to air. The neutron intensity at the higher scattering angles examined was successfully fitted using the Porod law, which is applicable to scattering from a twophase system at the high scattering angle limit. This limit is related to the specific surface area between the two phases. The limiting scattered intensity of neutrons was found to increase with increasing moisture content for a range of paper materials. It is concluded that the sorption of water increased the limiting intensity because water disrupted polymerpolymer bonding. The Porod law also predicts the slope of the intensity/scattering angle curve at the high scattering angle limit. © 2004, Walter de Gruyter