Effect of the distribution of substitution of the sodium salt of carboxymethylcellulose on its absorbency toward aqueous liquid

Abstract

An attempt was made to correlate the capacity of the aqueous liquid absorption of sodium salt of carboxymethylcellulose with its chemical structure, in particular with the total degree of substitution ‹‹F›› and distribution of substitution ‹‹fk›› Here, ‹‹fk›› is the average degree of substitution of hydroxyl group attached to Ck carbon (k=2, 3, and 6) in an anhydroglucopyranose unit. For this purpose, 26 samples of NaCMC having ‹‹fk›› less than 0.64 were synthesized by reacting cellulose having crystal form of cellulose I or II with a mixture of sodium hydroxide, monochloroacetic acid and 2-propanol. Their absorbency was determined at 37°C toward water, 0.9wt% aq. sodium chloride, calcium chloride and aluminium chloride solutions. ‹‹fk››+‹‹fk››, and ‹‹fk›› and ‹‹fk›› were determined for these polymers by 13C NMR in 10wt% sodium hydroxide–90 wt% D2O mixture. On using the cellulose with the crystal form cellulose II, carboxymethylation occurred almost preferentially at the hydroxyl group attached to the C6 carbon. This was not observed for the cellulose having the crystal form of cellulose I. Absorbency was found to be definitely governed by ‹‹fk››, which can be explained in consideration of the solid structure of cellulose and NaCMC. © 1985 The Society of Polymer Science, Japan.