Date of Award

1-2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Materials Science and Engineering

Advisor

Brown, Philip J

Committee Member

Cole , Christine

Committee Member

Lickfied , Deborah

Committee Member

Cox , Christopher

Committee Member

Mefford , Olin

Abstract

HEPA and ULPA filtration systems have proven to be an advantageous instrument in removing common contaminants from the air. However, an increased pressure drop due to the build-up of particulates on the filters results in its inevitable decrease in performance. Improving current filtration systems would include increasing collection efficiency all the while either maintaining or reducing the differential pressure drop in order to extend the life of the filter. One method of improving collection efficiency would be viable by increasing the amount of surface area within the filter media by glass fibers because of their inherent quality of being smaller in diameter offering more surface area than melt spun fibers. This research examined alternate methods of producing fibers comparable or smaller in size than glass fibers. As well, a unique geometry fiber know as a Capillary Channel Polymer (CCPTM) was examined for its contribution towards filtration since it offers at least twice the surface area as a round fiber of equal denier.
Nonwoven filter media were manufactured with CCPTM fibers and tested for collection efficiency and pressure drop. Although SEM images showed salt particles collecting within the grooves of the shaped fibers, they did not exhibit HEPA quality efficiencies. The pressure drop of these filters was low as compared to currently used M98 HEPA filters. This was potentially due to the CCPTM fibers being unable to pack as closely together as round glass fibers allowing for high air permeability which may have contributed to the lower collection efficiency and pressure drop. Modified melt blown round fibers were also examined since their fiber diameters measured within nano range and offered benefits in terms of ease of manufacturing. The nonwovens demonstrated HEPA quality collection efficiency but at a higher pressure drop than M98 media. The melt blown nonwovens, in addition to being thicker than the M98 media, lacked structural integrity which would allow them to be used alone as a filter. The effect of slip flow on fibers measuring less than 0.50 µm in diameter was analyzed for M98 and meltblown media. The meltblown sample which contained a higher amount of fibers within the slip flow regime and contained no scrim demonstrated HEPA quality collection efficiency when compared to the M98 media with comparable basis weight.
Dissolvable bi-component fibers were also examined for their potential to produce nano-size sea fibers separated by a wet-laid process. Bi-component fibers can be manufactured via traditional melt-spun lines and offer not only nano-size islands in round but also unique geometry cross-sections such as CCPTM. Difficulties in effectively dissolving off the polymer sea leaving behind individual islands prevented an in-depth examination of their contribution towards filtration. Composite media composed of CCPTM and meltblown layers proved unsuccessful in terms of collection efficiency as well as thickness but demonstrated low pressure drop. Further investigation into layering techniques and adding additional meltblowns may prove fruitful for filtration media.

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