This study aims to improve the understanding of the influence of metal oxide nanofillers on polyvinylidene difluoride (PVDF) ultrafiltration membranes. Zinc oxide nanoparticles were chosen as the model filler material. The membranes were prepared by non-solvent induced phase separation from PVDF solutions in N-methylpyrrolidone. The influences of the addition of polyvinylpyrrolidone (PVP), the nanoparticle dispersion quality, and a surface modification of the ZnO particles with PVP on the nanofiller integration into the polymer matrix and the resulting membrane separation performance, were evaluated. Unmodified and PVP-modified nanoparticles were characterized by evaluation of their Hansen solubility parameters. The membranes were characterized by ultrafiltration experiments, scanning electron microscopy (SEM) and with respect to mechanical properties, while the dope solutions were analyzed by rheology in order to judge about dispersion quality. Pure water permeability and solute rejection data revealed that the dominant effect of the addition of pristine ZnO nanoparticles was a major decrease in permeability caused by pore blocking. In SEM analyses, it was seen that the plain nanofiller did not integrate well into the polymer matrix. Importantly, it was found that the surface modification of the nanofiller, as well as a high dispersion quality, can be strategically used to enhance the integration of the nanofiller and thus suppress pore blocking, leading to membranes with high ultrafiltration rejection and permeability simultaneously. Overall, the study provides relevant insights into a new approach to integrating nanofillers into polymer nanocomposite membranes for improving their properties and performance.
Keywords: PVDF; ZnO; nanocomposite; nanofiller dispersion; phase separation; ultrafiltration membrane.