Experimental and theoretical studies on the formation of pure β-phase polymorphs during fabrication of polyvinylidene fluoride membranes by cyclic carbonate solvents

The use of highly toxic solvents presents significant risks to both the environment and human health. Therefore, the adoption of green solvents will be crucial for achieving sustainable membrane production. This work reports the use of inexpensive environmentally friendly biobased and biodegradable cyclic carbonate solvents, namely ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), to fabricate polyvinylidene fluoride (PVDF) membranes. The solvent dependence of the phase inversion mechanisms, morphology, crystalline structures, and polymorphism of the prepared PVDF membranes were investigated. Polymorph analysis revealed that membrane fabrication in EC or PC yielded exclusively the beta-phase product, whereas PVDF membrane fabrication in BC yielded a mixture of alpha and beta phase material. The mechanism of beta-phase formation was investigated using molecular dynamics simulation and shown to depend on the extent of hydrogen bonding at the polymer-solvent interface. The PVDF membrane formed in EC exhibited the highest porosity and pure water permeability, and was therefore tested in direct contact membrane distillation (DCMD), exhibiting promising results in terms of permeate flux and salt rejection. These results suggest that large-scale production of piezoelectric PVDF membranes using green solvents should be practically feasible.

Automated summary

The use of green solvents for polyvinylidene fluoride (PVDF) membrane fabrication was investigated in this study. Membranes fabricated in ethylene carbonate (EC) or propylene carbonate (PC) yielded exclusively the beta-phase product, while butylene carbonate (BC) led to a mixture of alpha and beta phase material. The PVDF membrane formed in EC exhibited the highest porosity and pure water permeability, showing promising results in direct contact membrane distillation (DCMD) for permeate flux and salt rejection. These findings suggest that large-scale production of piezoelectric PVDF membranes using green solvents is feasible.