Formation of a bicontinuous structure membrane of polyvinylidene fluoride in diphenyl carbonate diluent via thermally induced phase separation

Abstract

Diphenyl carbonate was used as a diluent to prepare microporous polyvinylidene fluoride (PVDF) membrane via thermally induced phase-separation method. The liquid-liquid phase-separation phenomenon was found in PVDF/diphenyl carbonate system during the thermally induced phase-separation process. The monotectic point of this system appeared at a high polymer concentration approximately 56 wt %. This suggested that PVDF membrane with a bicontinuous or cellular structure could be obtained when the PVDF concentration was less than this point value. The effects of polymer concentration and quenching temperature on the membrane structure, porosity, and tensile strength were also investigated. The results showed that low polymer concentration and high quenching temperature led to a large pore size membrane. The tensile strength of the membrane increased with increase in the polymer concentration, but the porosity of the membrane decreased. On condition that the PVDF concentration was higher than 60 wt %, only polymer crystallization occurred and a typical compact spherulitic structure was obtained.

Understanding the non-solvent induced phase separation (NIPS) effect during the fabrication of microporous PVDF membranes via thermally induced phase separation (TIPS)

“…Therefore, an interesting conclusion can be deduced in which the spherulitic morphology results in mechanically fragile membranes, possibly worse than membranes with macrovoids. Hence, much of the recent TIPS research has focused on inducing a bicontinuous structure while minimizing spherulite formation [48,49].…”

Fabrication of a dual-layer (CA/PVDF) hollow fiber membrane for RO concentrate treatment

“…The membranes were then rinsed in an ethanol bath for 24 h to remove the residual solvent. The hollow fiber membranes were dried in air at ambient temperature and then divided into fibers for further posttreatments [9]. The fabricated PVDF membranes in the first step were immersed in DMSO for 10 s as an intermediate-treatment, to avoid the severe blocking of the inner layer pores by the CA polymers of outer layer, during the dip-coating of CA dope solution.…”

“…The inner layer was fabricated with the PVDF hollow fiber membrane via the TIPS process [9]. Briefly, three hollow fiber membranes were fabricated by the PVDF solution and quenched into tap water at 25°C.…”

“…A two-step interfacial polymerization (IP)/NIPS process was proposed to fabricate a thin film composite (PA/PES/PVDF) hollow fiber NF membrane [9]. In contrast, the NIPS process showed a simpler approach to fabricate the outer layer of dual-layer hollow fiber membrane, while the pure water permeability (PWP) was inferior to that of the single-layer asymmetric membranes, due to the poor porosity of inner layer by the interfacial blocking [10].…”

An improved process for polyvinylidene fluoride membrane preparation by using a water soluble diluent via thermally induced phase separation technique

“…Nowadays, the diluents such as diethyl phthalate (DEP) [10], sulfolane [11], dimethyl phthalate (DMP) [12], dibutyl phthalate (DBP) [13], diphenyl carbonate (DPC) [14], diphenyl ketone (DPK) [15] and acetyl tributyl citrate(ATBC) [16,17], are commonly used in PVDF membrane preparation. Obviously, these diluents are insoluble in water and alcohols must be used to wash final membranes to remove the diluents in the membranes.…”