THE EFFECT OF COOPERATIVE CHARGING ON FILTRATION PROPERTIES OF ELECTRICALLY DISSIMILAR ELECTROSPUN NANOFIBERS OF POLYMERS 6.1 Chapter Summary Electrical charging and residual charge decay of electrospun nonwoven webs

6.1 Chapter Summary Electrical charging and residual charge decay of electrospun nonwoven webs comprised of two electrically dissimilar polymers were studied in an effort to investigate their filtration properties. Electrospinning of polystyrene (PS) and polyacrylonitrile (PAN) was performed by utilizing three different approaches to produce thin fibrous webs: PAN and PS were electrospun individually in a ‘single component’ fashion; in a ‘layer-by-layer’ configuration; and simultaneously in a side-by-side ‘bicomponent’ apparatus to yield bicomponent fibers. During electrospinning of the PS and PAN polymer solutions, the fibers were found to become positively charged when a positive voltage (+15kV) was applied to the solution-filled spinning nozzle and were found to become negatively charged when a negative voltage (-15kV) was applied to the spinning nozzle. This study allowed the examination of the effect of the electrospinning on inducing charges of different polarity on two electrically dissimilar polymers, viz. PAN and PS, and to determine the effect of the three types of web constructions (‘single component’, ‘layer-by-layer’ and ‘bicomponent’) on charge retention and filtration properties of the resulting nanofibers. It was found that single, multilayered, and bicomponent webs retained surface charges in the thousands of volts that diminished very little over a 20-hour period, but eventually bled off while in storage for three months. Filtration properties were found to be exceptionally high for some, but not all, electrospun samples; filtration was found to have a weak dependence on both surface charge and web geometrical factors, particularly the fiber diameter, that influence pressure drop of the aerosol.