Synthesis of carboxymethyl starch

Carboxymethyl starch (CMS) was obtained under heterogeneous conditions as a product of the reaction of starch and monochloroacetic acid (MCA) in the p resence of sodium hydroxide. The influence of the composition of the reacti on mixture, the reaction time and temperature and the type of starch being carboxymethylated on the degree of substitution, DS, and limiting viscosity number, [eta], was studied. The reaction temperature influenced the DS val ues, the highest values of the DS being obtained when the carboxymethylatio n was performed at 58 degreesC. Increase of the molar ratio of NaOH to anhy droglycose units leads to an increase in DS, but only to certain extent. Th e values of the DS and [eta] of CMS increased almost linearly with increasi ng MCA amount in the reaction mixture. The reaction mixture changes caused by adding water to ethanol influenced the DS values of the obtained CMS sam ples, the maximum DS value being obtained for CMS sample synthesized in eth anol with 25% (v/v) water.