Free radical degradation of hydroxyethyl cellulose

The degradation of hydroxyethyl cellulose (HEC) using sodium persulfate (NaPS) as free radical generator was studied at 60, 70 and 80 °C with different NaPS/HEC ratios. During the degradation reaction samples were withdrawn at regular intervals. The amount of persulfate remaining was analyzed by titration and the evolution of the HEC molecular weight distribution and viscosity was followed using size exclusion chromatography (SEC) and rheology, respectively. The results show how the molecular weight of HEC is decreased by varying the NaPS/HEC ratio, reaction time and temperature. It was found that the NaPS/HEC ratio must be kept low in order to maintain the control of the degradation process, since when the NaPS/HEC ratio was too high the degradation rate of HEC was too fast, and the molecular weight distribution became bimodal. Additionally, the decomposition rate of NaPS was found to be independent of pH in the range between pH 2 and 7.