Browsing by Subject "nonwovens"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Producing Melt Blown Nano-/Micro-fibers with Unique Surface Wetting Properties(2015-09) Wang, ZaifeiMelt blowing is a one-step process producing microfibers with an average fiber diameter (dav) of 1 – 5 μm. One application of melt blown fibers is filter media of water-in-diesel engine fuel filtration. In order to meet the increasingly higher requirements on fuel cleanliness, enhancing the filter efficiency has been desired. One attractive strategy is applying nanofibers (dav < 1 μm). The other is modifying the fiber surface wetting properties, such as superhydrophobic. The goal of this work is to produce melt blown nano-/micro-fibers with superhydrophilic and/or superhydrophobic surfaces for water-in-diesel filtration. In this thesis, we advanced the new technique of producing nanofibers from melt blown fiber-in-fiber polymer blends by understanding the nanofiber formation and developing water-extractable nanofibers. Firstly, poly(styrene) (PS)/poly(butylene terephthalate) (PBT) and PS/poly(ethylene-co-chlorotrifluoroethylene) (ECTFE) binary blends were melt blown followed by tetrahydrofuran (THF) extraction. The control extrusions demonstrated that the core nanofibers were primarily generated during the fiber blowing process. We speculate that both aerodynamic and fiber-fiber drag influence the nanofiber formation. Varying the minor phase volume fraction revealed the nanofiber breakup. We proposed that both the single-droplet-elongation and dumbbell-formation contribute to the formation of nanofibers. In addition, we hypothesize that the coalescence leads to the formation of non-uniform nano-/micro-fibers. Following the discussion on nanofiber formation, we showed nanofiber fabrication from water-extractable melt blown fiber-in-fiber polymer blends containing a water-dispersible sulfopolyester (SP). This new method eliminates issues associated with organic solvents. Also, it provides another route to prepare multilayer nano-/micro-fiber composites. Surface wetting modifications of melt blown PBT fibers were achieved by alkaline hydrolysis and subsequent fluorination. Application of alkaline hydrolysis generates sponge-like PBT fibers decorated with hydroxyl and carboxyl functional groups, resulting in a superhydrophilic fiber mat surface. The subsequent fluorination creates a sticky-superhydrophobic surface. An alternative achieving enhanced or even superhydrophobic PBT fiber surfaces is incorporation of a random perfluorinated multiblock copolyester (PFCE). Adding only 5 wt% of PFCE into PBT leads to over 20 wt% of PFCE on PBT fiber surfaces. The blooming of fluorine and the overall mat roughness increased the water contact angle from about 128° to above 150° and lowered the fiber mat surface adhesion energy by 25%. Finally, the appendices show some preliminary works on: 1) synthesis and characterizations of poly(L-lactide) and perfluoropolyether block copolymer; 2) the effects of alkaline hydrolysis on surface topography and mechanical properties of melt blown PBT fiber mats; 3) compatibilized polyamide 6 and poly(ethene-co-tetrafluoroethene) (PETFE) blends, which, however, were not suitable for melt blowing due to high viscosity; 4) collection of individual melt blown nanofibers.Item Thermoset Films and Nonwovens via Thiol-Ene Photopolymerization(2021-12) Lau , ChristieThiol-ene photopolymerization is a simple, versatile method to form thermosets rapidly at high yields. This thesis focuses on studying the structure-property relationships of three thiol-ene photocured networks formed from biobased, dual-curable, and hybrid components. The photocurable resins were first developed through bulk studies and then applied in forming thermoset nonwovens via a simultaneous electrospinning and UV curing process. Unlike conventional fiber spinning methods, the reactive fiber spinning approach requires significantly less solvent and leads to the formation of thermoset fibers, which generally have better thermal and chemical stability compared to thermoplastic fibers. For the biobased networks, two carbohydrate-based monomers were reacted with tetra-thiols to form thermosets. The monomers had subtle chemical substituent differences yet led to unexpectedly large differences in mechanical properties that were attributed to their different molecular geometries. This study highlights an important reality when using bioderived feedstocks in that they can possess subtle chemical substituent differences that can translate to polymers with vastly different thermophysical properties. The bioderived monomers were subsequently used to form nonwovens, and the fibers readily degraded into small molecules in basic aqueous media. Dual-curable polyurethane-(meth)acrylate networks containing thermally labile urea linkages were also formed via photopolymerization. Subsequent heating triggers a network rearrangement process, facilitated in part by reactions between newly exposed isocyanates and diols, which also improves the material’s toughness. In processes that require fast reaction kinetics, such as reactive fiber spinning, monomers with high functionalities are often required and the resulting thermosets are tightly crosslinked and brittle. This dual-cure system overcomes such limitations by first setting the fiber morphology rapidly via photopolymerization and utilizing a second stimulus (heat) to transform the network, which defines the materials’ final thermophysical properties. Finally, hybrid networks containing tri-acrylates and tetra-thiols as the stiff components and polybutadiene as the elastomeric component were formed. Besides obtaining bulk hybrid thermosets with phase-separated structures, successful formation of fibers was demonstrated, which cannot be attained via conventional fiber spinning methods due to the liquid character of polybutadiene. This strategy to form fibers from materials with low Tg was also demonstrated for other elastomers, as evidenced by the successful formation of fibers containing polydimethylsiloxane.