Effect of salts and surfactant and their doses on the gelation of extremely dilute solutions of methyl cellulose

The effect of different salts and surfactant and their doses on the gel temperature of extremely dilute solutions (below 1%) of methyl cellulose (MC) has been studied. The gel temperature decreases non-linearly (concave downward) with increase in MC concentration. The addition of salts like NaCl, (NH4)(2)SO4 and (Na)(2)CO3 lowers the gel temperature of MC due to its dehydration. But increase in gel temperature is also observed on addition of 0.5 and 1% NaCl to 0.6 and 0.7% MC solutions, respectively. The addition of 1% sodium carbonate causes appearance of clouds only up to 0.2% MC, cloudy gel followed by dear gel up to 0.3% MC, thereafter phase separation occurs even at room temperature. The effect of addition of a surfactant, sodium lauryl sulphate (SLS) on the process of gelation of aqueous MC solutions has been studied in detail. The gelation process depends on I; the ratio of weight% of surfactant and that of MC present in the aqueous solution. Gels are formed For the limit 0.02 < r < 0.1 for all MC solutions, beyond which phase separation occurs. With increase in r (from the lower limit), gel temperature increases, reaches a maximum and then decreases. (C) 2000 Elsevier Science Ltd. All rights reserved.