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Nonwovens in filtration - a worthy challenge.

Nonwovens In Filtration--A Worthy Challenge Take the word "filtration." What is it and what does it do?

Webster's Unabridged dictionary defines a "filter" as "a device for separating solid particles, impurities, etc. from a fluid by passing it through a porous substance. Any porous substance can be used for this purpose, such as sand, charcoal or felt. In physics, a, a device or substance that passes electric currents of certain frequencies or frequency ranges while preventing the passage of others; b, a device or substance that partially or completely absorbs light rays, as a color for a camera lens."

Another definition from the Macmillan Dictionary states that it is "a device for straining solids or impurities from a liquid or gas." To understand these definitions, you may want to define the words "separating" and "straining" as they would be applied in an actual situation. It is interesting that in this dictionary, filter was listed just before "filth," and it defines that word as "something that is foul or putrid, offensive dirt or refuse," then uses the following sentence as an example. "Industrial filth pollutes the air and water"--excellent opportunities for filters.

There are, of course, other definitions that are directed towards a specific application. Detailed specifications become a necessity when we find a word such as blood in front of the word filter, denoting where and how it is to be used and its performance requirements. However, there are those filters on the other end of the spectrum, such as those used in home window air conditioners or heating systems. The typical consumer that buys them only wants to know if it fits his unit. He assumes it will stop multi-engine aircraft and carnivorous mammals from entering his den...and it should be cheap.

Difficult, Complicated and Confusing

Some of the basic concepts of ow a filter performs a given function have changed and evidently will continue to change as the need to separate, collect and contain expands with our personal, business and environmental needs. As an example, we could see our industry begin to categorize filters into such groups as separation, collection and containing, with subcategories such as wet/dry, air, disposable, self fitting/moldable, rigid, size, pore/opening, chemical reactions, raw materials and numerous other identifying nomenclature.

Filtration is one of the most difficult product areas to define, complicated to categorize and confusing to one entering the field of attempting to market products to this vast and growing arena. The number of different raw materials used include fiber, wovens, knits, nonwovens, sand-clay-earth, rock, metal, ceramic, charcoal, electronic principles and apparatus, a host of chemicals/compounds and others.

There are other means and methods also used such as centrifuges, gravity and flotation, as well as human fingers. Today we find many of these used in a single operation. Such as operation may incorporate fire/burning and/or air currents in one state utilizing specific gravity and/or floatation, while another stage may use magnetic attraction, chemical dissolving or neutralizing and still another may have baghouse and other types of fibrous materials that may pulse, rotate or remain in a fixed position.

One of the current interest in the nonwovens industry that has incorporated numerous filtration principles is the recovery and reprocessing of polyester. Most of this has involved polyester (PET) soft drink bottles where those involved wanted to make textile grade fiber from it. Although several major fiber companies have been using their internal PET waste in a similar manner for years, this project involved numerous other factors. Removing metal caps, paper/plastic labels, olefin base portions and, of course, various consumer additives such as cigars and bobby pins inside the bottles are just a few of these factors.

The short version of this story is that this is an on-going business today. Bottles are being collected after being used by the consumer, processed into fiber and sold to the producers of nonwovens and other products. It is a very complicated and expensive operation, but it works. Will there be changes in their methods of separating and reprocessing these materials in the future? Can a fish swim?

A filter "protects" a patient during an operation or a microelectronic device during assembly, it "separates" the good or more desirable from the other allowing a more profitable situation, it "collects" and "contains" that which we wish to hold, further process or dispose of in a controlled manner and it will perform functions in the future that we have not conceived today.

Filtration will offer excellent opportunities for nonwovens in the future because we have vast process and raw material capabilities. Our processes can arrange various fibers or blends of fibers in numerous configurations, include chemical additives, materials can be made light/heavy/wide/narrow and in layers/laminates and composites. Our processes can make filtration materials that are rigid, flexible, moldable, stretchable, with the capability to stop bacteria or to allow a horse and carriage to drive through without being touched.

Most manufacturers of nonwovens are participating in this market today. Every type of nonwoven is presently being used in some type of filter application. Our industry can assist in developing and producting filtration products to make the world a better place in which to live while offering us a profitable business for our future.

For Your Information

In the December, 1990 Holliday Talk column, "the Process of Comparing Nonwovens," a legend for the chart on page 8 was inadvertently ommitted. The letters in Table 1 stand for: Y = Yes, N = No, L = Limited and P = Possible. In addition, the heading at the top of the left hand column should read Fabric Property Capabilities. We regret any problems this ommission may have caused. If any reader requires an updated copy of this chart, please contact the editor.

Tom Holliday is a well known consultant to the nonwovens and textile industries whose column on a wide range of nonwovens-related topics appears every month in Nonwovens Industry. Mr. Holliday operates his consultancy firm, Thomas M. Holliday & Associates out of his office at 25 Edgewood Road, Yardley, PA 19067; (215) 493-2501.
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Author:Holliday, Tom
Publication:Nonwovens Industry
Article Type:Cover Story
Date:Feb 1, 1991
Words:1018
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