Development of degree of etherification methods in ASTM D -1439 for NaCMC

Sodium carboxymethyl cellulose (NaCMC), which is formed by alkalizing cellulose with sodium hydroxide and then etherifying it with monochloroacetic acid or sodium salt, is one of the most widely used cellulose derivatives. The product groups from which sodium chloride and sodium glycolate, which are formed as by-products as a result of the reaction, are removed are called pure-type NaCMC, while the group from which no purification process is performed is called technical-type NaCMC. The degree of substitution (SD), which indicates the number of groups displaced in the etherification reaction, is one of the most important parameters affecting the final properties of NaCMC. The internationally accepted standards for measuring the SD value are IS 3520:1992 (2019) and ASTM D-1439 (2022) Method-A and Method-B standards. Due to its low reproducibility rate, the IS method has recently lost its popularity internationally and has been replaced by ASTM D-1439 methods. According to ASTM D-1439 Standard, which is divided into two different methods, technical type and NaCMC types with SD value up to 0.85 can be analyzed with Method-A, while pure type and all types with SD value can be analyzed with Method-B. While a limited SD value can be measured with Method A, at the same time, low repeatability results are obtained due to manual back titration in the method. At this point, a new and highly repeatable method is needed for NaCMC types with SD value higher than 0.85, which has a wide commercial usage area. The aim of this study is to develop a method that will meet the specified needs and to analyze all SD values of technical and pure type NaCMCs with high accuracy and repeatability rate with this developed method. In this study, 375 SD analysis were performed.