Electrospinning of poly(vinyl alcohol) and poly(vinyl alcohol)/tannin solutions: A critical viewpoint about crosslinking

Abstract

Poly(vinyl alcohol) (PVA) is a hydrophilic and cytocompatible polymer used in biomedical, pharmaceutical, food, and environmental applications. However, the PVA aqueous solubility restricts its direct application. To overcome this disadvantage, PVA chains can be chemically crosslinked to impart stability and durability to the engineered materials. This work presents PVA/Tanfloc (PVA/TN) electrospun fibers for the first time. TN is an amino-functionalized polyphenolic tannin derivative. PVA/TN materials were created from PVA/TN blends in water (W)/acetic acid (HAc) (99/1 v/v) and W/formic acid (FA) (50/50 v/v) mixtures. FA and glutaraldehyde (GA) were evaluated as crosslinkers for the electrospun fibers. GA vapor was also tested as a crosslinker. PVA and PVA/TN materials (before and after crosslinking) were characterized by infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The as-prepared PVA/TN fibers quickly dissolved in ethanol and water but not in acetone. Fiber durability increased in acetone when the TN content was at least 20 wt%. PVA/TN fibers were crosslinked in acetone containing GA (1.0 wt%) and HAc (1.0 % v/v). However, GA-crosslinked fibers had no stability in water after washing. The stability of PVA-based electrospun fibers after GA crosslinking has not been previously reported in the literature. PVA/TN fibers were also crosslinked by thermal treatment. This strategy maintained the fiber structure after water immersion over 15 days. This study presents a critical viewpoint concerning strategies to crosslink PVA-based fibers, focusing on fiber durability and stability after crosslinking. The thermal treatment is by far the best method to crosslink PVA-based fibers because it can maintain fiber morphology, promoting aqueous durability.