Inhaltszusammenfassung

The hydration of cellulose, chitosan, schizophyllan, hyaluronan, and carboxymethyl cellulose was studied using differential scanning calorimetry (DSC). In the first part, the classical freezing/thawing approach was used to determine the amount of non-freezing water. The inconsistency in enthalpies obtained during crystallization and melting of freezable water was discussed with respect to the DSC experimental conditions. Our interpretation questions the recent conclusions about competitive pr...The hydration of cellulose, chitosan, schizophyllan, hyaluronan, and carboxymethyl cellulose was studied using differential scanning calorimetry (DSC). In the first part, the classical freezing/thawing approach was used to determine the amount of non-freezing water. The inconsistency in enthalpies obtained during crystallization and melting of freezable water was discussed with respect to the DSC experimental conditions. Our interpretation questions the recent conclusions about competitive processes occurring during melting which are hypothesized to influence the determined melting enthalpy. In the second part, the hydration and drying were studied using the evaporation enthalpy of water. The dry mass normalized dependency of vaporization enthalpy on water content confirmed an abrupt break at low water content in hyaluronan sample which was attributed to the sudden appearance of a parallel process taking part during the drying. The rest of polysaccharide samples showed only a linear decrease in evaporation enthalpy. The renormalization of enthalpies by the water content revealed the increase in evaporation enthalpy with decreasing water content in most samples which was ascribed to the strong interaction between polysaccharide and water. The exceptions were carboxymethyl cellulose which showed a decrease in evaporation enthalpy. This indicates the existence of a simultaneous process occurring during drying, but unlike in hyaluronan, the processes do not appear abruptly but accompany the evaporation in the wide concentration range. Comparison of determined hydration numbers showed that part of non-freezing water in hyaluronan is not bound to sorption sites but occurs presumably in small temporary pores. In contrast, water-soluble schizophyllan forms temporary pores as well but presumably with higher dimension and the non-freezing water is formed mostly by water molecules interacting with sorption sites. » weiterlesen» einklappen

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