Influence of rheology and surface properties on morphology of nanofibers derived from islands-in-the-sea meltblown nonwovens

• Published in: Polymer (Guilford) Vol. 145; pp. 21 - 30
• Main Authors: Soltani, Iman, Macosko, Christopher W.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 06.06.2018; Elsevier BV
• Subjects: Attenuation; Blowing; Bundling; Chemical bonds; Coalescence; Coalescing; Drop size; Ethylene; Fiber diameter distribution; Fiber in fiber; Fiber morphology; Fibers; Flow rates; Flow velocity; Fluorides; Hydrophilic; Hydrophobic; Hydrophobicity; Interfacial tension; Island-in-the-sea morphology; Islands; Mats; Meltblown; Morphology; Nanofiber; Nanofibers; Organic chemistry; Polybutylene terephthalate; Polybutylene terephthalates; Polyethylene terephthalate; Polymer blends; Polymer melt processing; Polymers; Polyvinylidene fluorides; Resins; Rheological properties; Rheology; Shear viscosity; Surface energy; Surface free energy; Surface properties; Viscosity; Viscosity ratio; Water chemistry; Water soluble polymers; Hydrophilic; Nanofiber; Meltblown; Island-in-the-sea morphology; Viscosity ratio; Surface free energy; Fiber morphology; Fiber in fiber; Interfacial tension; Attenuation; Coalescence; Fiber diameter distribution; Rheological properties; Hydrophobic
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2018.04.051

Melt blowing is the most common technique to directly produce nonwovens from polymeric resins without any demand for extra bonding steps. The relatively low diameter of meltblown fibers, 1–2 μm, makes them superior in separations performance to the competing melt processing technique, spun-bonding. To further decrease meltblown fiber diameter, the islands-in-the-sea approach was investigated in this study. Immiscible blends of a water-soluble polymer, sulfonated poly(ethylene terephthalate) (SP), and hydrophilic polybutylene terephthalate (PBT) and hydrophobic polyvinylidene fluoride (PVDF) were meltblown and the SP washed away to produce nanofibers of less than 200 nm diameter. Despite a significant increase in blend drop size upon increasing the minor phase fraction, ϕ, the nanofiber diameter increased only slightly. Thus, we conjecture that nanofiber diameter is mainly controlled by fiber pinch-off, induced by quick stretching during the melt blowing process, rather than being affected by initial drop size. At a high shear viscosity ratio, ηminor/ηmatrix > 3, nanofibers showed a higher level of irregularities, particularly when the polymer flow rate decreased. At ϕ ≥ 0.2 fiber bundling was observed but with nanofibers from PVDF, due to its lower surface energy, compared with PBT, bundling decreased. Our work shows that using polymers with relatively low surface energy, and thus low tendency for coalescence, coupled with low viscosity can result in nonwoven mats of fibers with very low average diameter, low bundling, and an acceptable fiber regularity. With PVDF we achieved a record low average diameter of 36 nm. By using a water-soluble polymer matrix, such as sulfonated poly(ethylene terephthalate), concerns about cost and environmental problems related to chemical solvents are alleviated. [Display omitted] •Nanofibers by melt blowing polymer blends.•Wash away the water soluble matrix polymer.•36 nm PVDF fibers.