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Abstract
Fully hydrolyzed polyvinyl alcohol (FH-PVA) electrospun fibers with uniform diameters of less than 200 nm were fabricated by reducing the viscosity of FH-PVA aqueous solutions. A novel viscosity-modifier (hydrazine monochloride [HMC]) gradually reduced the viscosity of FH-PVA aqueous solution over a period of several days. This phenomenon is counter to the effect of the usual salt addition. After being stored for several days, the viscosity decreased by up to 60% compared with that of an equivalent pure FH-PVA solution. From small angle X-ray scattering (SAXS) and proton nuclear magnetic resonance (^sup 1^H NMR) spectra observations it is evident that this effect results from the reconfiguration of hydrogen bonding. The viscosity control of FH-PVA solutions with HMC were used to electrospin highly uniform ultrafine fibers (diameter <200 nm).
Keywords
polyvinyl alcohol (PVA), electrospinning, ultrafine fibers, hydrogen bonding, viscosity-modifier
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Polyvinyl alcohol (PVA) is a water-soluble synthetic polymer produced industrially by the hydrolysis of polyvinyl acetate.1,2 Many different grades of PVA are commercially available, falling into two types, depending on the degree of hydrolysis (DH), fully hydrolyzed PVA (FH-PVA) and partially hydrolyzed PVA (PH-PVA).3-5 The higher chemical stability, water resistance, and excellent physical and mechanical properties of FH-PVA have led to its wide use, especially in the textile industry.1
Electrospinning is a relatively simple and inexpensive method to produce fibers with diameters in the nanometer range.6-10 PVA is one of the most popular polymers used for ultrafine electrospun fiber production. Nano-scale PVA fibers have several interesting characteristics, such as high surface area to mass ratio, significant possibilities for surface functionalization, and high mechanical performance due to an improvement in the molecular organization of the spun fiber. These properties make electrospun PVA fibers excellent candidates for many applications, such as filtration, reinforcing materials, wound dressings, tissue scaffolding, and drug-releasing carriers.11-16 FH-PVA is frequently described as a good material for producing nano-scale electrospun fibers;17,18 however, it is difficult to fabricate electrospun FH-PVA fibers with diameters below about 200nm due to the extremely high surface tension and viscosity of the solution. 19 It has been suggested that reducing the high surface tension of FH-PVA in solution will address this problem.20,21 However, although the surface tension can be demonstrably modified, controlled production of FH-PVA electrospun...