Influence of different non-solvent additives to the casting solution on the structure and properties of PES membranes

The effect of the precipitation value (PV) of mixtures of strong and weak non-solvent additives (NSA) on the phase state and viscosity of polyethersulfone(PES)/dimethylacetamide(DMAc)/non-solvent solutions and on the structure and performance of PES membranes were studied. Polyethylene glycol 400 (PEG-400, PV > 1000), water (PV = 10.6), 85 % phosphoric acid (PV = 13.0), glycerol (Gly, PV = 27.8) and mixtures thereof were used as NSA for PES-DMAc solutions. Using Gly/PEG-400 mixtures it was established that the increase in PV of NSA leads to the increase of a miscibility gap on the phase diagram. At a constant concentration of Gly/PEG-400 mixture, the viscosity of the solutions decreases. For a constant ratio (0.94–0.95) of the NSA amount added to the polymer-solvent system to the NSA amount causes a phase separation of the casting solution (coagulation value) increase in PV of NSA Gly/PEG-400 leads to an increase of the membrane pure water flux (PWF) from 13 up to 150 l/m2 h at 1 bar. The most dramatic increase in PWF occurs in the range of PV 39.7–125 g/dL. The results of SEM study don’t show significant differences in the cross-section morphology of membranes for different PV of NSA. However, the thickness of the selective membrane layer increases from 1 up to 4.5 μm when PV increased from 39.7 up to 750 g/dL. Thus, these studies allow us to conclude that the structure and properties of ultrafiltration membranes depend not only on the coagulation value of the casting solution, but also on the precipitation value of NSA.

1. Liu Y., Koops G. H., Strathmann H. Characterization of morphology controlled polyethersulfone hollow fiber membranes by the addition of polyethylene glycol to the dope and bore liquid solution. Journal of Membrane Science, 2003, vol. 223, no. 1–2, pp. 187–199. https://doi.org/10.1016/s0376-7388(03)00322-3

2. Wang Z., Ma J. The role of nonsolvent in-diffusion velocity in determining polymeric membrane morphology. Desalination, 2012, vol. 286, pp. 69–79. https://doi.org/10.1016/j.desal.2011.11.006

3. Holda A. k., Vankelecom I. F. J. Understanding and guiding the phase inversion process for synthesis of solvent resistant nanofiltration membranes. Journal of Applied Polymer Science, 2015, vol. 132, no. 27, app. 42130. https://doi. org/10.1002/app.42130

4. Xu Z. l., Qusay F. A. Polyethersulfone (PES) hollow fiber ultrafiltration membranes prepared by PES/non-solvent/ NMP solution. Journal of Membrane Science, 2004, vol. 233, no. 1–2, pp. 101–111. https://doi.org/10.1016/j.memsci.2004.01.005

5. Idris A., Norashikin M. J., Noordin M. y. Synthesis, characterization and performance of asymmetric polyethersulfone (PES) ultrafiltration membranes with polyethylene glycol of different molecular weights as additives. Desalination, 2007, vol. 207, no. 1–3, pp. 324–339. https://doi.org/10.1016/j.desal.2006.08.008

6. Chakrabarty B., Ghoshal A. k., Purkait M. k. Effect of molecular weight of PEG on membrane morphology and transport properties. Journal of Membrane Science, 2008, vol. 309, no. 1–2, pp. 209–221. https://doi.org/10.1016/j.memsci. 2007.10.027

7. Shin S.-J., kim J.-P., kim H.-J., Jeon J.-H., Min B. Preparation and characterization of polyethersulfone microfiltration membranes by a 2-methoxyethanol additive. Desalination, 2005, vol. 186, no. 1–3, pp. 1–10. https://doi.org/10.1016/j. desal.2005.03.092

8. Torrestiana-Sanchez B., ortiz-Basurto R. I., Brito-De la Fuente E. Effect of nonsolvents on properties of spinning solutions and polyethersulfone hollow fiber ultrafiltration membranes. Journal of Membrane Science, 1999, vol. 152, no. 1, pp. 19–28. https://doi.org/10.1016/s0376-7388(98)00172-0

9. Wang D., li k., Sourirajan S., Teo W. k. Phase separation phenomena of polysulfone/solvent/organic nonsolvent and polyethersulfone/solvent/organic nonsolvent systems. Journal of Applied Polymer Science, 1993, vol. 50, no. 10, pp. 1693– 1700. https://doi.org/10.1002/app.1993.070501003

10. Wang D., li k., Teo W. k. Relationship between mass ratio of nonsolvent-additive to solvent in membrane casting solution and its coagulation value. Journal of Membrane Science, 1995, vol. 98, no. 3, pp. 233–240. https://doi.org/10.1016/0376-7388(94)00191-z

11. Pratsenko S. A., Bildyukevich A. V. Structure of casting solutions and its effect on the characteristics of polyamide membranes. Polymer science, Ser. А, 1994, vol. 36, no. 3, pp. 457–460 (in Russian).

12. Bildyukevich A. V., Pratsenko S. A., Plisko T. V. Influence of pore-generators on properties of polyethersulfone membranes. Khimicheskaya Tekhnologiya [Chemical Technology], 2012, vol. 13, no. 3, pp. 174–178 (in Russian).

13. Feng y., Han G., Chung T.-S., Weber M., Widjojo N., Maletzko C. Effects of polyethylene glycol on membrane formation and properties of hydrophilic sulfonated polyphenylenesulfone (sPPSU) membranes. Journal of Membrane Science, 2017, vol. 531, pp. 27–35. https://doi.org/10.1016/j.memsci.2017.02.040

14. lai J.-y., lin F.-C., Wang C.-C., Wang D.-M. Effect of nonsolvent additives on the porosity and morphology of asymmetric TPX membranes. Journal of Membrane Science, 1996, vol. 118, no. 1, pp. 49–61. https://doi.org/10.1016/0376-7388(96)00084-1

15. Chun k.-y., Jang S.-H., kim H.-S., kim y.-W., Han H.-S., Joe y. Effects of solvent on the pore formation in asymmetric 6FDA–4,4′oDA polyimide membrane: terms of thermodynamics, precipitation kinetics, and physical factors. Journal of Membrane Science, 2000, vol. 169, no. 2, pp. 197–204. https://doi.org/10.1016/s0376-7388(99)00336-1