Electrospun poly(vinyl alcohol) (PVA) nanofiber membranes were functionalized by incorporating either poly(methyl vinyl ether-alt-maleic anhydride) (PMA) to create negative charges, or poly(hexadimethrine bromide) (PB) and chitosan (CS) to create positive charges on the fiber surface. The functionalized PVA nanofiber membranes were heat-treated at elevated temperatures to impart cross-linking and improve the water-resistance. The optimum heat-treatment temperatures for both PVA/PMA and PVA/PB/CS systems were screened by Fourier transformed infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Formation of cross-linked structure and increased crystallinity were triggered by the heat-treatment. A cationic dye, methylene blue (MB), and an anionic dye, acid red 1 (AR1), were used to represent charged moieties in solution. The surface-charged PVA nanofiber membranes were able to selectively capture counter-charged dye molecules from aqueous solutions. The capture processes obey the pseudo-second-order kinetic model. The capture equilibrium can be well-described by the Langmuir model. Chemically cross-linked PVA/PMA nanofiber membranes exhibited higher strength in capturing counter-charged dyes than physically cross-linked PVA/PB/CS nanofiber membranes. Selective chemical capture studies indicated that, by tailoring the surface, functionalized PVA nanofiber membranes were able to selectively remove charged chemicals with potential applications for purifying mixed liquids and delivering a pure sample for detection in small-scale testing systems.
In this work, electrospun poly(vinyl alcohol) (PVA) nanofiber membranes were functionalized by incorporating poly(methyl vinyl ether-alt-maleic anhydride) (poly(MVE/MA), PMA) for the selective adsorption of proteins. The capture performance was regulated by an optimizing buffer pH, PMA content, and protein concentration. Lysozyme was used as the model protein and a high adsorption capacity of 476.53 ± 19.48 was obtained at pH 6, owing to the electrostatic attraction between the negatively charged nanofibers and positively charged proteins. The large specific surface area, highly open porous structure, and abundant available carboxyl groups contributed to such high adsorption performance. Moreover, the nanofiber membranes exhibited good reusability and good selectivity for positively charged proteins. The obtained results can provide a promising method for the purification of proteins in small analytic devices.
A non-acid-based, di-functional epoxide, neopentyl glycol diglycidyl ether (NPGDGE), was used to modify cotton fabrics. Direct characterization of the modified cotton was conducted by Nuclear Magnetic Resonance (NMR) without grinding the fabric into a fine powder. NaOH and MgBr were compared in catalyzing the reaction between the epoxide groups of NPGDGE and the hydroxyl groups of cellulose. Possible reaction routes were discussed. Scanning electron microscopy (SEM) images showed that while the MgBr-catalyzed reaction resulted in self-polymerization of NPGDGE, the NaOH-catalyzed reaction did not. Fourier transform infrared spectroscopy (FTIR) showed that at high NaOH concentration cellulose restructures from allomorph I to II. NMR studies verified the incorporation of NPGDGE into cotton fabrics with a clear NMR signal, and confirmed that at higher NaOH concentration the efficiency of grafting of NPGDGE was increased. This demonstrates that use of solid state NMR directly on woven fabric samples can simultaneously characterize chemical modification and crystalline polymorph of cotton. No loss of tensile strength was observed for cotton fabrics modified with NPGDGE.
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