Interaction and phase separation in the system HPMC/NaCMC/SDS

In this work, the interaction in the ternary system composed of two cellulose derivatives, anionic—sodium carboxymethylcellulose (NaCMC) and nonionic-hydroxyprophylmethylcellulose (HPMC), and anionic surfactant—sodium laurylsulfate (SDS) has been investigated by rheological measurements. Rheological measurements were performed at 20 °C using a rotational viscometer and by applying a continuous loop hysteresis method. The mass ratios of the HPMC/NaCMC in 1.0% solution were: 0.3/0.7; 0.5/0.5; 0.7/0.3, while SDS concentration increases from 0 to 2.0%. In such a system, depending on the mass ratios of the components, various interactions between HPMC–NaCMC, HPMC–SDS and NaCMC–(HPMC–SDS) takes place. The phase separation in solution was followed by turbidity and height of coacervate layer measurements.The investigations show that HPMC and NaCMC molecules interact with each other and synergistic effect on viscosity was observed. This synergistic effect disappears with SDS addition. As a result of the interactions in ternary system HPMC/NaCMC/SDS, the phase separation, i.e. coacervation occurs at particular mass ratios of the components. The coacervate formation depends on the HPMC–SDS interaction and influences turbidity and viscosity of the system.