Characterisation of water behaviour in cellulose ether polymers using low frequency dielectric spectroscopy.

Abstract

The behaviour of water in hydroxypropylmethylcellulose (HPMC) K100LV, K4M, K15M, K100M, E4M, F4M and HPC polymers was characterised using low frequency dielectric spectroscopy (LFDS). Dielectric responses of 25% (w/w) HPMC K15M gels and deionised water were found to be similar at +22 and 0 degrees C. However, at -30 degrees C, a dielectric response typical of a solid was apparent. The melting of frozen water within gels was detected as increases in the magnitude of the dielectric response with increase in temperature. More than one phase transition was visible in the majority of gels studied which may be related to the presence of different states of water melting at different temperatures. In addition to polymer concentration, both polymer molecular weight and substitution level influenced the nature of the transitions. The magnitude of the dielectric response was increased in all HPMC gel systems in comparison to the response seen in deionised water. Drug addition affected the transitions occurring during the melting of ice in the gels. This may be related to the presence of ionic species in the systems. LFDS studies on cellulose ether gels have provided some interesting evidence for the existence of more than one state of water within such gel systems. The results are in good agreement with thermal analysis findings in similar gel systems.