Nanostructured Chitosan Membranes for Filtration

Chitosan is a non-toxic and biodegradable biopolymer derived from naturally occurring chitin. It has excellent metal binding and anti-microbial properties which could be beneficial in air and water filtration applications. Nanofibers have distinctly high surface area to volume ratio.

Electrospinning is a process by which nano-sized polymer fibers can be produced using an electrostatically driven jet of polymer solution. The fibers are collected as a non-woven mat and offer a high surface area to volume ratio.

Electrospinning of pure chitosan is hindered by its limited solubility in aqueous acids and high molecular weight with high degree of inter and intra chain hydrogen bonding. We have been able to form nanometer sized fibers without bead defects by electrospinning Chitosan blends with different polymers like poly (ethylene oxide) and poly (acrylamide) with up to 95% chitosan in blend fibers. The electrospinning apparatus was modified so at to be able heat solutions during electrospinning which helps in expanding the processing window. Fiber formation is controlled by polymer molecular weight, blend ratios, polymer concentration and spinning solution temperature.

Surface chemistry of these blend fibers was characterized using XPS. XPS data validated that chitosan content on fiber surface was a function of % chitosan in blend, degree of deacetylation of chitosan, and fiber diameter. A theoretical model was developed which predicted the binding properties of chitosan fibers with known fiber diameter, % chitosan in blend and degree of deacetylation. Surface properties of blend fibers showed a strong correlation with the structure and morphology of the fibers and higher chromium binding capacities compared to similar blend ratio chitosan films were observed. A nanofibrous filter media has been fabricated by electrospinning a layer of chitosan nanofibers onto a non-woven spun bonded poly propylene fabric. These coated filter media have been tested for their metal binding and anti-microbial properties and results showed applicability towards effectively filtering heavy metals and bacteria from waste media. The filtration performance of these nanofibrous filter media have been tested against latex polystyrene beads and aerosol particles and filtration efficiencies of these media were a function of pore size, fiber diameter and size of filtrate.