Preparation and characterization of PVDF membranes incorporated with different additives for dyeing solution treatment using membrane distillation

In this work, the properties of pristine polyvinylidene fluoride (PVDF) hollow fiber membranes were altered by incorporating different types of additives, that is, ethylene glycol (EG) and polyvinylpyrrolidone (PVP) into dope solution. Prior to the separation process, the resulting membranes were first characterized with respect to structural morphology, hydrophobicity, overall porosity, gas permeability, wetting pressure, mechanical, and thermal stability. It is found that PVP has major impact on the membrane structural properties due to the PVP residue in the membrane matrix. The PVP has transformed the PVDF membrane into hydrophilic ones, while EG did not negatively affect the hydrophobicity of the PVDF membrane. During direct contact membrane distillation process, it is reported that both membranes were able to achieve at least 99% rejection of reactive black 5 when tested under counter-current flow condition. Compared to the PVDF–PVP membrane, the experimental results showed that the PVDF–EG membrane demonstrated greater stabilities of flux and rejection during 5 h study period, mainly due to its greater hydrophobicity and higher wetting pressure which play a role in preventing the liquids from both sides penetrating through membrane pores and further minimizing membrane fouling.