Electrospun Polymer Nanofibers Reinforced by Tannic Acid/Fe Complexes.

We report the successful preparation of reinforced electrospun nanofibers and fibrous mats of polyvinyl alcohol (PVA) via a simple and inexpensive method using stable tannic acid (TA) and ferric ion (Fe) assemblies formed by solution mixing and pH adjustment. Changes in solution pH change the number of TA galloyl groups attached to the Fe from one (pH < 2) to two (3 < pH < 6) to three (pH < 7.4) and affect the interactions between PVA and TA. At pH ~ 5.5, the morphology and fiber diameter size (FDS) examined by SEM are determinant for the mechanical properties of the fibrous mats and depend on the PVA content. At an optimal 8 wt % concentration, PVA becomes fully entangled and forms uniform nanofibers with smaller FDS ( < 0.05) and improved mechanical properties when compared to mats of PVA alone and of PVA with TA ( < 0.05). Changes in solution pH lead to beads formation, more irregular FDS and poorer mechanical properties ( < 0.05). The Fe inclusion does not alter the oxidation activity of TA ( > 0.05) suggesting the potential of TA-Fe assemblies to reinforce polymer nanofibers with high functionality for use in diverse applications including food, biomedical and pharmaceutical.