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Access type: UnknownAuthor: search.filters.author.Gunasekaran, Sundaram

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    Enthalpy relaxation in sucrose-maltodextrin-sodium citrate bioglass
    (2017-10-01)
    Sritham, Eakasit
    ;
    Gunasekaran, Sundaram
    Glass transition characteristics of sucrose (SC)-maltodextrin (MD)-sodium citrate (NaCit) bioglass system were investigated using differential scanning calorimetry. Samples were formulated with different SC:MD (7:3, 5:5 and 3:7 by mass) and NaCit/SC (0, 0.1 and 0.2 by mole) ratios, and were equilibrated to residual moisture contents of 0.27–0.35 %wb. Isothermal aging experiments were conducted with the degree of undercooling from 12 to 57 °C and aging times of 8, 20, 47 and 71 h. In general, the Kohlrausch-Williams-Watts (KWW) decay function fit well with the experimental enthalpy relaxation data. The enthalpy relaxation time (τ<sup>KWW</sup>) and the time required for 50% completion of theoretical possible maximum enthalpy relaxation at constant temperature (t<inf>ϕ(t)=0.5</inf>) increased with increasing MD content; lowering the aging temperature had similar effects on τ<sup>KWW</sup> and t<inf>ϕ(t)=0.5</inf>. In the system with high SC and NaCit concentrations (SC:MD = 7:3 and NaCit/SC = 0.2), a substantial increase in τ<sup>KWW</sup> and t<inf>ϕ(t)=0.5</inf> were observed when aging temperature <inf>decreased slightly;</inf> these systems also exhibited the greatest apparent activation energy. The findings reveal that NaCit can enhance the stability of low-moisture bioglass by primarily interacting with SC and form large less-mobile clusters, which helps to improve glass transition temperature and restrict the matrix mobility.
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    FTIR spectroscopic evaluation of sucrose-maltodextrin-sodium citrate bioglass
    (2017-09-01)
    Sritham, Eakasit
    ;
    Gunasekaran, Sundaram
    A model bioglass system was composed with sucrose (SC), maltodextrin (MD), and sodium citrate (NaCit). Samples were prepared with different SC/MD ratios (7:3, 5:5 and 3:7, by mass) and NaCit/SC ratios (0, 0.1 and 0.2, by mole) at low (0.27–0.49 %wb) and high (2.83–4.4 %wb) levels of moisture content. The effects of system constituents were investigated using the Fourier transform infrared (FTIR) spectroscopy. Hydrogen bonding interactions analyzed by studying the OH-stretching absorption band in the FTIR spectra indicated that there was no noticeable effect of moisture on the bioglass. The matrix of the system with high concentration of MD was loosely packed. NaCit interacted with both SC and MD through carboxylic groups, as evidenced by the shifting of antisymmetric (ν<inf>as</inf>(COO<sup>−</sup>)) and symmetric (ν<inf>s</inf>(COO<sup>−</sup>)) stretching bands of carboxyl groups. However, NaCit tended to interact more strongly with SC rather than with MD as evidenced by the strongest hydrogen-bonded network observed in the system with highest concentrations of SC (i.e., SC/MD = 7:3) and NaCit (i.e., NaCit/SC = 0.2).
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    Rheological and microstructure evaluations of amorphous sucrose-maltodextrin-sodium citrate mixture
    (2017-01-01)
    Sritham, Eakasit
    ;
    Gunasekaran, Sundaram
    Rheological properties and the mechanical relaxation behavior of rubbery amorphous sucrose-maltodextrin-sodium citrate systems were studied at room temperature using the small amplitude oscillatory shear test in the frequency range of 0.1 - 150 Hz. The system with high sucrose concentration exhibited viscous-dominant relaxation, while the system with high maltodextrin concentration exhibited elastic-dominant relaxation. The addition of sodium citrate could retard molecular mobility presumably due to its molecular interaction with sucrose rather than with maltodextrin. The technique was capable to detect changes in molecular process even with a small variation in the matrix components. Evidences obtained with scanning electron micrographs suggested the possible effect of sodium citrate to interfere with molecular interactions in the system with high maltodextrin concentration, i.e. the system tended to be more brittle.