Phase diagram of novel recycling aqueous two-phase systems composed of two pH-response polymers: Experiment and modeling

• The phase diagram of ATPS composed of two pH-response polymers was constructed.
• The effect of pH on binodal curves and tie lines of the ATPS were investigated.
• Polymer concentration to form ATPS at high pH was higher than low pH.
• Two models were used to correlate the equilibrium data of PADB/PADBA ATPS.
• Flory–Huggins model had better results in correlating PADB/PADBA ATPS than NRTL model.

To solve recyclable problem of aqueous two-phase systems (ATPS), novel recycling ATPS were constructed by two novel pH-response copolymers (PADB and PADBA) in our lab. In this study, the phase diagram of PADB/PADBA aqueous two-phase systems was prepared. The effect of pH on the tie lines and binodal curves with 4.87, 5.45, and 6.05 at 25 °C were investigated. Two models including Flory–Huggins model and NRTL model were used to correlate the equilibrium data of PADB/PADBA aqueous two-phase systems. The interaction parameters between two polymers in the two models were determined by fitting experimental data to the objective function. The minimal RMSD of Flory–Huggins model is 0.8777 at pH 6.05 and in NRTL model is 1.0092 at pH 6.05. Flory–Huggins model shows better correlation than NRTL model for PADB/PADBA aqueous two-phase systems.