How To Separate Oil From Water By Electrospinning Nanofiber Technology?
1. COMPOSITE POLYMERIC NANOFIBROUS MATS
Due to the relatively weak mechanical strength of PS fibers and the unstable networks of the mats, the practical application performance (e.g., retention over time, oil recovery rate) of pure electrospun PS fibrous absorbents was seriously limited. To overcome this challenging problem, mechanical enhancers with high strength were introduced into the PS fibrous mats to improve their mechanical property. Various criteria must be fulfilled by the reinforcing components: they should be mechanically robust to withstand the tensile or compressive stresses during adsorption and recovery processes of sorbents; and hydrophobic-oleophilic wettability is required to ensure the mats have selective wetting ability. Accordingly, a series of additives such as polyvinyl chloride (PVC), polyurethane (PU), polyvinylidene fluoride (PVDF), and carbon nanotubes (CNTs) were employed to modify the PS fibers via different methods based on electrospinning technology.
To incorporate the reinforcing component into PS fibrous mats, various approaches involving blend electrospinning, multinozzle electrospinning, and coaxial electrospinning have been developed. As shown in Fig. 13.4A-C, PVC/PS composite fibers was first fabricated via directly adding an appropriate amount of PVC to PS solutions, and then made by blend electrospinning. The obtained oil absorbents performed well for motor oil, peanut oil, diesel, and ethylene glycol, with high sorption capacities of 146, 119, 38, and 81 g/g, respectively; these capacities are about five to nine times that of commercial PP melt-blown nonwoven sorbent. The PVC/PS oil adsorbent also possessed excellent oil-water selectivity and good buoyancy, which are important in oil-slick cleanup. Multinozzle electrospinning, a powerful technology in fabricating composite nanofibrous materials, has also been used to make porous PU/PS fibrous mats for oil absorption (Fig. 13.4D-F). The robust elasticity of the PU fibers greatly improves the mechanical strength of the obtained PU/PS fibrous mats, even with low PU contents. As a result the oil absorption performance, especially the reusability of the PU/PS fibrous absorbents, was significantly enhanced. Moreover, core-shell structured fibers were considered as an effective approach to enhance the mechanical property of single fibers. The SEM and the corresponding Transmission Electron Microscopy (TEM) images shown in Fig. 13.4G show that the core-shell structured PU-PS fibers have been prepared with a coaxial electrospinning technique by taking PU and PS solutions as the core and shell, respectively. The obtained PU-PS fibrous sorbent has sorption capacities of 64.40 and 47.48 g/g for motor oil and sunflower seed oil, respectively, which are two to three times that of traditional nonwoven PP fibrous mats with the same template oils (Fig. 13.4H and I). Moreover, the oil adsorption capacity comparable with melt-blown nonwoven sorbent was maintained even after five sorption cycles, giving excellent reusability.