Poly(vinylidene fluoride) membranes have been extensively applied to scientific research and industrial processes, because of their outstanding properties such as high thermal stability, good chemical resistance, and membrane forming properties.
Here researchers at the Dalian Institute of Chemical Physics in China review recent progress on the application and modification of PVDF membranes. The applications include water treatment, membrane distillation, gas separation, pollutant removal, bioethanol recovery, separators for lithium-ion batteries, supports for preparing composite membranes etc.
Fouling and wetting
In particular, on the basis of two major problems with PVDF membranes in real-world applications, i.e. membrane fouling and membrane wetting, hydrophilic modification and hydrophobic modification methods are comprehensively reviewed.
Furthermore, the key issues associated with the modification of PVDF membranes for actual applications are discussed. This work may provide an insight for the future development of PVDF membranes.
One of the applications covered is the extensive use of PVDF membranes in water treatment for general separation or purification purposes, for example reuse of municipal wastewater, pre-treatment of brine water prior to reverse osmosis (RO), concentration of fermentation broths etc.
A variety of PVDF membranes for microfiltration (MF), ultrafiltration (UF), and membrane bioreactor (MBR) processes have been developed to remove bacteria, viruses, suspended solids, emulsified oils, metal hydroxides, colloids, proteins, and organic matter from water or other solutions.
The major problem of PVDF membranes in water treatment applications is the tendency to fouling due to hydrophobicity, which can be improved by suitable hydrophilic treatments.
Hydrophilic modification includes physical and chemical methods. Both are effective in tailoring the surface properties of PVDF membranes, offering a better antifouling performance.
However, the modification process usually causes a decline in water flux. It is very necessary to reduce the additional permeation resistance – for example, decreasing the coating layer, developing new hydrophilic materials with inherently high water permeability, avoiding the blocking of membrane pores – in order to maintain the membrane efficiency.