Development of polyelectrolyte multilayer-coated electrospun cellulose acetate fiber mat as composite membranes

Electrostatic multilayers of chitosan (CHI)/sodium alginate (SA) and CHI/poly(styrene sulfonate) sodium salt (PSS) were alternatively coated on electrospun cellulose acetate (CA) fiber mat. Morphologies of the composite membranes were characterized by scanning electron microscopy. The morphology of the CHI/SA-coated membrane was denser than the CHI/PSS-coated one. The top layers consisted of carboxyl and sulfonic functional groups for SA and PSS layers, respectively. Amino groups of CHI were only presented in slight quantity. X-ray photoelectron spectroscopy (XPS) confirmed the deposition of the amino groups of CHI on the multilayer membrane surface. These composite membranes were characterized for its water permeability where the water flux decreased with an increase in the number of the bilayers. The water flux was in the range of 60 and 40 L m⁻² h⁻¹ for 15 and 25 bilayered membranes, respectively. The sodium chloride (NaCl) solution flux was lower than the pure water flux due to the effect of osmotic pressure, and it decreased with an increase in the NaCl concentration. The rejection of NaCl increased substantially with the number of the bilayers of the polyelectrolytes multilayers. The level of NaCl rejection from this work was in the range of 6% and 15% for 15 and 25 bilayered membranes, respectively.     

Electrospun dextran fibrous membranes

Ultra-fine fiber mats of dextran (powder; M _w = 64,000–76,000 Da) were fabricated by electrospinning, using water as the solvent. The effects of solution concentration (i.e., 0.7–1.3 g mL⁻¹) and applied electric field (9–21 kV/15 cm) on morphological appearance and size of the obtained fibers were investigated. Under a fixed electric field of 15 kV/15 cm and a fixed solution flow rate of 0.25 mL h⁻¹, beaded fibers were observed up to a critical concentration of about 0.9 g mL⁻¹, beyond which only smooth fibers were obtained. The average diameter of these fibers increased monotonically with increasing the solution concentration (i.e., from ∼290 to ∼1950 nm). For the dextran solutions investigated, increasing the electric field generally caused the diameters of the obtained fibers to increase, with the average diameter of the obtained fibers ranging between 520 and 1760 nm. To improve the usefulness of the electrospun dextran fiber mats in an aqueous medium, cross-linking with glutaraldehyde was necessary. The effects of curing temperature (i.e., 70–90 °C), curing time (i.e., 3–48 h), and added MgCl₂ catalyst (i.e., 0.01–0.03 g) on physical integrity of the cross-linked dextran membranes in water were investigated. Both the swelling and the weight loss in water of the cross-linked membranes were generally found to decrease with increasing curing temperature, curing time, and MgCl₂ loading and the cross-linking did not affect the morphology of the obtained membranes.