Preparation of hollow fibre membranes from PVDF/PVP blends and their application in VMD

Microporous hydrophobic poly(vinylidene fluoride) (PVDF) hollow fibres were prepared by the dry-wet spinning technique. N,N-Dimethylformamide (DMF) was used as solvent, while water and poly(vinyl pyrrolidone) (PVP) were used as pore forming additives. Mixtures of DMF or ethanol in water were employed as bore fluids. The influence of different parameters on the fibres characteristics was explored. Particular attention was focused on the PVP concentration and on the composition of the bore fluid. The obtained fibres exhibit good structure, excellent mechanical properties, high porosity (up to 80%) and an average pore size ranging from 0.12 to 0.27m. Fibres were tested in vacuum membrane distillation (VMD) configuration, using distilled water as feed. The effect of membrane properties on the water vapor fluxes was investigated. For the prepared membranes, the measured fluxes ranged between 3.5 and 18 kg/m2 h at 50 oC and 20 mbar vacuum pressure. Some selected fibres were assessed for long term stability. Constant performances were observed up to 2 months. Furthermore, preliminary VMD tests on salty water were also performed, in order to verify fibres suitability for seawater desalination.