Determination of acid substituents and unesterified hydroxyl groups in cellulose esters

The properties of mixed cellulose esters are strongly affected by the nature and ratio of acid substituents. Fast reliable methods are needed to determine the acid substituents of these products. For some applications it is necessary to also determine the unesterified hydroxyl content. A generally applicable method has been developed to determine acid substituents of mixed cellulose esters. The cellulose ester sample is rapidly hydrolyzed with a reagent consisting of a polar, aprotic solvent, for example dimethyl sulfoxide, with sodium hydroxide and methanol. The hydrolyzed acids are determined by reversed-phase liquid chromatography with UV detection. The results are sufficiently precise so that unesterified hydroxyl content can be calculated by difference.