Thermally stimulated current of solid pullulan

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Abstract
Thermally stimulated current (TSC) experiments have been performed on pullulan films in order to clarify the relation between the chemical structure and dielectric properties. These complex modes have been experimentally resolved into “elementary” processes characterized by relaxation times obeying Arrhenius equations: The corresponding activation energies, Ei have been measured. For the peak at +50°C: 0.63 < Ei < 1.1 eV. This mode has been attributed to motions of water molecules introduced during the hydration of the sample. For the peak at −50°C: 0.45 < Ei < 0.51 eV. This mode, which is also strongly dependent upon the water content of the sample, may be related to bound water. In slightly hydrated samples, the magnitude of the peak observed at −130°C is not affected by moisture. Regarding the values of activation energies—0.16 eV to 0.35 eV—the rotation of methylol groups at C5 is considered to be responsible for this process. A comparison with global spectra for amylose and dextran is made also, and the assumption is confirmed.

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