Hydration Of Ethyl Hydroxyethyl Cellulose

The hydration of ethyl hydroxyethyl cellulose (EHEC) has been investigated, utilizing three different methods: proton nuclear magnetic resonance, differential scanning calorimetry and water self-diffusion measurements. The results differ somewhat, depending on the method used, but lie around 2 g of bound water per g EHEC, which corresponds to about 30 water molecules per monomer unit. This is considerably higher than the more hydrophobic methyl cellulose and the more hydrophilic cellulose sulphate. The importance of ethylene oxide groups for water binding to EHEC is also reflected in differences in hydration between EHEC samples with different amounts of ethylene oxide groups. Mechanisms behind the observed hydration numbers are discussed and it is suggested that there is an important influence of water interaction with the polymer backbone. This is favoured by an increasing repulsion between the polymers when ethylene oxide groups are introduced.