4.3 Nanocellulose from carboxylic acids and their stability

To date, many different types of nanocelluloses are known with a range of dimensions and surface functionalities affecting the properties of the material and which applications they can be used for. One type of nanocellulose can be made through simultaneous esterification and hydrolysis of cellulose with oxalic acid. The reaction of cellulose with oxalic acid results in a cellulose ester (cellulose oxalate), that has a carboxylic acid attached through an ester bond. The stability of the cellulose oxalate ester towards base-catalysed hydrolysis was investigated through immersion in buffer solutions with pH ranging from 6 to 10. The results show that the ester is rapidly hydrolysed already within 24 h at pH above 8. It could also be concluded that the carboxylic acid functionality of the cellulose oxalate is relatively acidic (pKa of 3.8) and that for carboxylic group content determination through conductometric titration, the equivalence point and not the plateau should be used. The results from this study show that stability of the ester needs to be carefully considered when working with cellulose oxalate