High-performance PVDF membranes prepared by the combined crystallisation and diffusion (CCD) method using a dual-casting technique: a breakthrough for water treatment applications

Abstract

One of the most commonly used membranes for water treatment applications is polyvinylidene fluoride (PVDF) membranes prepared using the non-solvent induced phase separation (NIPS) method. Unfortunately, these membranes suffer from low permeances. The newly discovered combined crystallisation and diffusion (CCD) method, based on a unidirectional freezing approach, is a promising alternative to the NIPS method to make high-performance PVDF membranes. This work applies a novel but simple dual-casting technique to the CCD membranes, to substantially breach the limits of permeation performance set by the industry-favourite NIPS membranes without sacrificing the membranes’ separation capabilities. Using this technique, one can tailor the specific properties of a CCD membranes’ separation and support layers, by merely changing the dope compositions of the two cast layers. This is the first time that a technique such as this is so simple yet effective in producing pristine PVDF membranes with pure water permeances as high as 2400 LMH bar⁻¹ and mean flow pore sizes as small as around 30 nm. The high permeances of these novel membranes will considerably improve the technological and economic feasibility of many ultrafiltration processes such as wastewater treatment and drinking water production.