Crystallinity study of electrospun poly (vinyl alcohol) nanofibers: effect of electrospinning, filler incorporation, and heat treatment

This study aims to explore crystallinity variations of polyvinyl alcohol (PVA) as a result of electrospinning, filler addition, and heat treatment. Pure PVA and PVA nanocomposite fibers containing only nanohydroxy apatite (nHAp) and together with cellulose nanofibers (CNF) were electrospun. Electrospun nanofibers were heat treated at 180 °C for 8 h. The morphology of electrospun fibers was evaluated by scanning electron microscopy (SEM) while Fourier transform infrared spectroscopy, differential scanning calorimetry, and wide angle X-ray scattering were used to analyze nanofibers crystallinity. Un-treated electrospun nanofibers were shrank and lost their porous structure in water, while heat treatment of nanofibers caused stabilization of fibrous mats in boiling water. It was concluded that the crystallinity of electrospun PVA were considerably reduced compared to PVA powder due to formation of metastable—small and/or defective crystals. Adding small content (1 wt%) of nHAp led to increase in electrospun nanofibers crystallinity. However, incorporation of higher content of nHAp and CNF caused reduction of crystallinity most probably due to possible interactions among components which interrupt the orientation of macromolecules. All analyzing methods proved the crystallinity enhancement of nanofibers upon heat treatment which can be attributed mostly to water evaporation from electrospun fibers structure.