Development of Polysulfone Hollow Fiber Porous Supports for High Flux Composite Membranes: Air Plasma and Piranha Etching

Ilya Borisov,Rais Mozhchil,Alexandr Bildyukevich,Galina Bondarenko,Alexey Volkov,Rustem Gallyamov,Vladimir Volkov,Rustem Ibragimov,Anna Ovcharova,Danila Bakhtin,Stepan Bazhenov

doi:10.3390/fib5010006

Abstract

For the development of high efficiency porous supports for composite membrane preparation, polysulfone (PSf) hollow fiber membranes (outer diameter 1.57 mm, inner diameter 1.12 mm) were modified by air plasma using the low temperature plasma treatment pilot plant which is easily scalable to industrial level and the Piranha etch (H2O2 + H2SO4). Chemical and plasma modification affected only surface layers and did not cause PSf chemical structure change. The modifications led to surface roughness decrease, which is of great importance for further thin film composite (TFC) membranes fabrication by dense selective layer coating, and also reduced water and ethylene glycol contact angle values for modified hollow fibers surface. Furthermore, the membranes surface energy increased two-fold. The Piranha mixture chemical modification did not change the membranes average pore size and gas permeance values, while air plasma treatment increased pore size 1.5-fold and also 2 order enhanced membranes surface porosity. Since membranes surface porosity increased due to air plasma treatment the modified membranes were used as efficient supports for preparation of high permeance TFC membranes by using poly[1-(trimethylsilyl)-1-propyne] as an example for selective layer fabrication.

Highlights

Multilayer composite membranes for the membrane separation technologies on molecular level, e.g., gas separation, pervaporation, reverse osmosis, and organic solvent nanofiltration are increasingly attractive due to their advantages over integrally skinned asymmetric (Loeb-Sourirajan) membranes
Outer surface of the virgin HF membrane, as well as air plasma and piranha mixture treated membranes images are shown in Figure 5a–c, respectively
It is clear that air plasma modified fiber has macroscopic defects on the outer surface and it proves that plasma does affect the membrane

Summary

Introduction

Multilayer composite membranes for the membrane separation technologies on molecular level, e.g., gas separation, pervaporation, reverse osmosis, and organic solvent nanofiltration are increasingly attractive due to their advantages over integrally skinned asymmetric (Loeb-Sourirajan) membranes. The development of thin-film composite (TFC) hollow fiber membranes is one of the major breakthroughs of membrane technology for large-scale industrial applications because of two main reasons: (i) composite membranes contain less than 1 g of the custom-made, high cost selective polymers per square meter of the membrane; and (ii) hollow fiber modules provide the high membrane. To deposit thin-film defect-free selective layer, a high efficiency porous support for TFC membrane preparation is needed. The porous structure of PSf membrane, as well as the properties of the surface (surface free energy, the presence of functional groups, micro-roughness) can significantly affect the transport properties of composite membranes produced. Porous PSf hollow fiber supports can be used to growth thin layers of microporous materials (e.g., MOFs—metal-organic frameworks, see [7]) for gas separation application

Methods

Results

Conclusion