A study on the interaction of water and cellulose ethers using differential scanning calorimetry

Differential scanning calorimetry (DSC) has been used to examine the distribution of water within hydroxypropylmethylcellulose 2208 (HPMC K15M) gels. Thermal events were apparent in the DSC scans of HPMC K15M gels which were dependent on their storage time, the concentration of the polymer and the cooling and heating rates utilised during DSC. Two or more thermal events were present on the low temperature side of the melting endotherm for gels (20-35% w/w HPMC K15M) in the -15 to 0 degrees C range. These may indicate the presence of different types of water in the gels. The number of moles of non-freezing water per polymer repeating unit HPMC K15M was estimated for gels as similar to 8 mol after 24 h and similar to 3.8 mol after 96 h storage. It is suggested that hydrating water is released from the polymer during equilibration between 24 and 96 h storage. (C) 1997 Elsevier Science B.V.