HYDRATION DEHYDRATION PROPERTIES OF METHYLCELLULOSE AND HYDROXYPROPYLMETHYLCELLULOSE

The degree and rates of hydration and dehydration of methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) play important roles in many commercial applications involving the use of these polymers. MC and HPMC are known to exhibit phase separation and associated gelation of aqueous solution which is caused by a decrease in stability in the hydrated polymer above the lower critical solution temperature. Hydration-dehydration phenomena of these solutions were studied using turbidimetric and microcalorimetric methods. The precipitation characteristics were observed by monitoring changes in percent light transmission with temperature. These measurements indicate a functional dependence of type and degree of substitution, molecular weight and uniformity of substitution. Scanning microcalorimetry experiments indicate that MC precipitates out of solution in a simple gelation process, while HPMC solutions exhibit broad peaks, which suggests molecular weight or branching effects. Heats of dehydration follow a linear relationship with total substitution. Hydration and rate of hydration can also be altered by controlled surface crosslinking and particle size. The importance of these hydration and rate of hydration phenomena in ceramic applications, as an example, will be illustrated.