Effects of calcium carbonate nano-particles on the properties of PVDF/nonwoven fabric flat-sheet composite membranes for direct contact membrane distillation

• PVDF flat-sheet composite membranes were prepared for membrane distillation.
• Influence of nano-particles on membrane properties was investigated.
• The calcium carbonate nano-particles narrowed membrane pore size distribution.
• The calcium carbonate nano-particles enhanced membrane roughness and contact angle.
• The composite membrane presented excellent permeability and performance stability.

The polyvinylidene fluoride (PVDF) flat-sheet composite membranes were prepared for membrane distillation using hydrophilic polyester nonwoven fabric as a support and the mixture of LiCl and PEG as non-solvent additive through coating and wet phase inversion process. The effects of hydrophobic calcium carbonate nano-particles on membrane morphology, porosity, pore size, pore size distribution, hydrophobicity, thermal properties and permeability were investigated. The nano-particles optimized membrane structure, enlarged pore diameter, narrowed pore size distribution and improved membrane porosity to some extent. In addition, the nano-particles could also enhance membrane surface roughness and contact angle while increasing the crystallinity degree of the prepared membranes. Nonetheless, the excess nano-particles addition would deteriorate membrane structure, reduce membrane porosity and decrease pore size. During the desalination process of 35 g/L sodium chloride solution, the maximum transmembrane permeate flux about 49.37 kg/m2h was obtained with the feed solution at 83 ºC and the cold distillate water at 20.0 ºC. Furthermore, the flat-sheet composite membrane exhibited satisfying performance stability compared with the membrane without nano-particles addition in the 300 h continuous desalination experiments, indicating that the prepared PVDF/nonwoven fabric flat-sheet composite membrane may be of great potential to be utilized in membrane distillation process for desalination.