Development of a polyvinylidene difluoride membrane for nanofiltration

Integrally skinned asymmetric nanofiltration (NF) membranes are widely used for treating a variety of aqueous and solvent streams. Polyvinylidene difluoride (PVDF), is an excellent film forming polymer with outstanding chemical, thermal and mechanical stability. However, additive-free PVDF membranes with pores small enough to apply them in NF do not currently exist. By accurately tuning the phase inversion parameters (i.e. polymer concentration, co-solvent concentration and evaporation time), a membrane was obtained that retains for 80% a 327 Da solute from an aqueous solution at a permeance of 1.8 LMH/bar when operated at 10 bar. The membranes were characterised by XRD and SEM, while the membrane formation process was characterised using viscosity measurements and cloud point determinations.