Preparation of PVDF/PTFE hollow fiber membranes for direct contact membrane distillation via thermally induced phase separation method

Development of polyvinylidene fluoride (PVDF) hollow fiber membranes by novel thermally induced phase separation

“…Firstly, with the addition of TEP, smaller spherulites in a higher density were formed due to enhanced polymer-diluent interaction during the TIPS process, which can reduce the pore size. Similar reductions in the pore size due to a higher density of spherulites were reported in our previous study (Zhao et al 2018). Secondly, the pores were opened up in a large amount as a result of solvent-nonsolvent (TEP/water) exchange, which can be supported by the increase in the pore size and porosity as shown in Figure 5.5(b).…”

“…This simple method is expected to allow us to tune the surface pore structure of membranes effectively without forming mechanically weak macrovoids, and to scale up membrane fabrication easily. Specifically, the water immiscible plasticizer, DMP, was used as the main diluent for PVDF since the hollow fiber membranes prepared from the PVDF/DMP dope mixtures exhibited an outstanding mechanical strength in our previous work (Zhao et al 2018). TEP was used at a low concentration together with DMP for PVDF fabrication in an effort to control the solvent-nonsolvent concentration gradient and to avoid the occurrence of gelation.…”

“…In this study, we selected 30 wt% as the polymer concentration to ensure that there was adequate viscosity for continuous processing based on our previous study (Zhao et al 2018). At the selected polymer concentration, the TIPS process is more likely to develop along the route of solid-liquid (S-L) phase separation instead of the liquidliquid (L-L) phase separation (Lloyd et al 1990, Zhao et al 2018. In addition, it also shows that 200 °C is high enough to guarantee the homogeneity of dope solutions at all polymer concentrations.…”

Fabrication and characterization of poly(vinylidene fluoride)–polytetrafluoroethylene composite membrane for CO2 absorption in gas–liquid contacting process

“…The amount of PTFE nanoparticles on the membrane outer surface increased proportionately with the increase employment of PTFE, which was favorable to the improvement of the surface hydrophobicity of the composite membrane. The membrane morphology obtained in this study is somewhat different from other PVDF–PTFE composite membranes fabricated previously in the field of membrane distillation . However, for the gas–liquid membrane contact process, a large number of finger‐like pores with PTFE nanoparticles on the surface are advantageous for reducing mass transfer resistance and wetting degree, so the current composite membranes are expected to achieve high absorption fluxes.…”

“…Therefore, combining advantages of both membrane materials to fabricate PVDF–PTFE composite hollow fiber membranes might be a promising approach to the improvement of resistance to wetting and chemical corrosion. Several researchers have tried to obtain PVDF–PTFE composite membranes by dispersing PTFE into PVDF solution and apply them in the field of membrane distillation . PTFE was proven to be a hydrophobicity enhancement agent; meanwhile, its addition has an effect on the change of membrane microstructure.…”