Electrospun poly(vinyl alcohol) nanofibers: effects of degree of hydrolysis and enhanced water stability

INTRODUCTION Poly(vinyl alcohol) (PVA) is a highly hydrophilic, nontoxic and biocompatible semicrystalline polymer with excellent properties such as strength, water solubility, gas permeability and thermal characteristics. PVA is available in a variety of degrees of hydrolysis (DH) because it is derived from the hydrolysis (or alcoholysis) of poly(vinyl acetate) (PVAc).1–3 The properties of PVA are therefore affected by DH. A PVA with DH between 87 and 89% has lower mechanical and water resistance than a PVA with DH between 98 and 99.9%. Consequently, the potential to interact with other polar polymers would be expected to vary as a function of DH. In recent years, electrospinning has become of great interest, not only because it can produce polymer fibers with diameters in the range of nanoto a few micrometers using polymer solutions or melts but also because it has the advantage of being a simple, conventional method with which a wide range of porous structures can be produced, as well as being inexpensive as compared with conventional methods.4–8 The electrospinning of the PVA solution has been extensively studied for the preparation of ultrafine separation filters, biodegradable mats and inorganic fibers. The dissolution of PVA depends on the nature of the solvent, the temperature and the extent of hydrolysis in the polymer. Depending on the rheological characteristics of the solution, electrospinning of a polymer solution can produce a variety of structures, mostly including beads, beaded fibers and fibers.9,10 Various solution parameters affecting the morphology and diameter of electrospun PVA fibers, such as the solution concentration, molecular weight,11 pH,12 salt,13 surfactant molecules14 and so on, have been investigated. However, the effect of DH on the morphology and diameter of electrospun PVA fibers has been less studied. In addition, PVA forms excellent nanofibers through electrospinning, but its applications are limited by its high hydrophilicity, through which it dissolves immediately on contact with water. Therefore, PVA fibers have been modified by either chemical15 or physical16 crosslinking to improve their mechanical properties and water resistance. In this study, we report the effects of DH on the morphology and diameter of electrospun PVA fibers and also explore the water resistance of electrospun PVA/poly(acrylic acid) (PAA) composite fibers through heat treatment.