(306d) Island-in-the-Sea Meltblown Nanofiber Nonwovens with Diverse Surface Properties for Filtration Applications

Melt-blowing is the most usual technique to directly produce nonwovens from polymeric resins. The relatively low thickness of meltblown fibers, 1-2 µm, makes them superior to the competing melt-processing technique, spun-bonding, regarding separation performance. To further improve this feature of meltblowing technique, by decreasing the fibers diameters, the island-in-the-sea approach was investigated in this study. Therefore, initially, immiscible blends were made of polymers with different dissolution, rheological, and surface properties. The successive meltblowing process resulted in microfiber nonwovens with internal island-in-the-sea structures. Finally, upon dissolution of the polymeric matrix with appropriate solvents, nanofiber nonwovens remained. It was noticed that, while meltblown microfiber diameter decreases with reducing their blends components viscosities, thinner extracted nanofibers are processed with decreasing both relative viscosity and interfacial tension of blends. In addition, by using a water-soluble polymer, sulfonated polyethylene terephthalate, existing concerns about cost and environmental problems related to chemical solvents are alleviated. Despite a significant increase in the droplet size in the blend, upon increasing the minor phase fraction, the nanofiber diameter increases almost slightly. Thus, it can be conjectured that nanofiber diameter is mainly controlled by the fiber pinch-off, induced by quick stretching during the melt blowing process, rather than being affected by the initial blend droplet size. Nanofibers resulted from the blends with high relative shear viscosity, η_minor/η_matrix>3, showed a higher level of regularities, particularly when the polymer flow rate decreases. Moreover, with an increase in the dispersed phase content irregularities like bundling of nanofibers increases, which may be a result of their coalescence, while being extruded and meltblown. Also, in the case of fibers from polyvinylidene fluoride (PVDF), due to its lower surface energy, compared with polybutylene terephthalate (PBT), bundling decreases to result in its more significant attenuation of droplets into nanofibers upon meltblowing. In summary, nonwoven mats of hydrophilic PBT and hydrophobic PVDF nanofibers of 100-200 nanometer diameters were made, by applying island-in-the-sea approach through meltblowing process, to provide the opportunity of engineering them towards desired filtration applications.