A study of the enzymic degradation of CMC and other cellulose ethers

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Abstract
Accelerated enzymic degradation of a series of six sodium carboxymethylcelluloses (CMC) varying in degree of substitution (DS) from 0.41 to 2.45 demonstrated that stability improves with increasing substitution, the DS 2.45 sample being essentially refactory to enzyme attack. The concentration of completely unsubstituted anhydroglucose (AHG) units in these samples, determined by acid hydrolysis followed by a glucose assay, is less at all substitution levels than would be expected from the relative etherification rates of the C2, C3, and C6 hydroxyls reported in the literature. Assuming random distribution of the unsubstituted AHG units, the frequency of single (IU) and multiple adjacent (xU) sequences can be predicted. Consideration of the extent of enzymic degradation, expressed in terms of the decrease in average molecular chain length deduced from [η] measurements, indicated that in CMC chain scission occurs only at xU sites. A limited comparison of the performance of methyl‐, hydroxyethyl‐, and hydroxypropylcelluloses under identical conditions revealed that, by contrast, in these ethers enzyme‐induced chain scission is possible not only at xU but also adjacent to 1U. The hydroxyalkyl and methyl groups appear to offer approximately equivalent protection against enzyme attack.
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