Fabrication of PVDF ultrafiltration membrane using modified thermally induced phase separation: The role of amphiphilic and hydrophilic non-solvents.

The use of amphiphilic pore formers and hydrophilic non-solvents has demonstrated its effectiveness in improving the surface porosity and permeability of polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes through the nonsolvent induced phase separation (NIPS) process in literatures. However, in the thermally induced phase separation (TIPS) process, few reports illustrated how the amphiphilic pore-former and water-soluble non-solvent interact with water-insoluble diluents. In this study, water-insoluble dimethyl phthalate (DMP) was used as the main diluent to rule out the effect of diluent outflow. The amphiphilic pore former polyethylene glycol 400 (PEG400) failed to open pores on the outer surface of the membranes because of its amphiphilic nature. On the contrary, UF membranes with a mean pore size of 55 nm could be obtained by adding hydrophilic triethylene glycol (TEG) to the dope with a satisfactory pure water permeability (PWP) of 262.6 L m−2 h−1 bar−1. Moreover, PEG400 can serve as a stabilizer for the TEG droplets during the phase separation if both were added to the polymer dope solution. The addition of both PEG400 and TEG could significantly increase the membrane's PWP to 645.4 L m−2 h−1 bar−1 with moderate enlargement of the mean pore size of the membrane to 84 nm. Additionally, the well-connected membrane structure resulted in the tensile strength of the membranes ranging from 3.07 to 6.65 MPa. This study expands the range of additives used in the TIPS process and demonstrates the different roles of amphiphilic and hydrophilic non-solvents in the TIPS process. [Display omitted] • The effects of hydrophilic and amphiphilic non-solvent in the TIPS process are analyzed. • Hydrophilic non-solvent TEG could tailor the surface morphologies of the PVDF membranes. • Amphiphilic PEG failed to open pores on the outer surface of the PVDF membrane. • Amphiphilic PEG served as the stabilizer of TEG in the PVDF dope, increasing the porosity and pore size of the membranes. • The resulting PVDF membranes sit within the UF range, presenting narrow pore distribution and high pure water permeability. [ABSTRACT FROM AUTHOR]