Page 177 - Carrahers_Polymer_Chemistry,_Eighth_Edition

140 Carraher’s Polymer Chemistry

Assemblies similar to the above have been employed to create images in clocks and watches and
other similar LCD image-containing products.

4.19 MICROFIBERS

Microfibers are not a new chemically distinct fiber, but rather the term refers to fibers that have

smaller diameters. DuPont first introduced microfibers in 1989. Microfibers have diameters that are

less than typical fi bers. Microfibers are half the diameter of fi ne silk fiber, one-quarter the diameter

of fi ne wool, and one hundred times fi ner than human hair. Denier, the weight in grams of 9,000-

meter length of a fiber, is the term used to define the diameter or fineness of a fiber. While the defi -

nition for the thickness of microfibers is varied, a typical definition is that microfibers have a denier

that is 0.9 denier or less. For comparison, the nylon stocking is knit from 10 to 15 denier fi ber.

Microfibers allow a fabric to be woven that is lightweight and strong. Microfibers can be tightly
woven so that wind, rain, and cold do not easily penetrate. Rainwear manufacturers use microfi bers
for this reason. They also have the ability to allow perspiration to pass through them. Thus, so-
called microfiber athletic-wear is becoming more common place. Microfibers are also very fl exible

because the small fi bers can easily slide back and forth on one another. The first fabric made from
TM

microfiber was Ultrasuede where short polyester microfibers were imbedded into a PU base.
Today microfibers are made mainly from polyesters, nylon, acrylic, and rayon fi bers.

The use of the term microfibers is now extended to glass and Teflon-related materials. Here we

will restrict ourselves to only fabric applications.
In 1970, Toray Industries scientist Miyoshi Okamoto created the fi rst microfi ber. A few months
later his colleague Toyohiko Hikota developed a process that allowed the production of fabric that
TM
was later trademarked as Ultrasuede . Ultrasuede was produced from PET polyester fibers so thin

that a pound of them laid end-to-end would reach from the earth to the moon and back. Ultrasuede
is soft and supple, resistant to stains and discoloration, and machine washable and dry cleanable.
Because of progress made in spinning and fiber processing, smaller fibers can be routinely made

with varying configurations, coatings, and so on. Microfiber production is mainly achieved using

three techniques. The first technique will be illustrated using the processing technique employed to

manufacture Ultrasuede.

The processing to form Ultrasuede is complex. First, ultramicrofibers are spun that are so light
and fine that a single 50-miles long strand would weight less than one gram. These ultramicrofi -

bers are then extruded through spinnerets creating a configuration that is similar to that present

in tendons and hair bundles. These strands are then transformed by ironing, curling, cutting, and
needle-punching into a felt-like material that is then impregnated with a special adhesive binder.
The material is then formed into the desired contours and the protective coating is dissolved with a
solvent and the material undergoes further processing creating the nonwoven fabric.

Microfibers are also made by simple extrusion through a spinneret with a smaller hole than

normally employed for fiber production. The third method involves spinning a bicomponent fi ber

and using a solution to split the fiber into smaller pieces. Initially, bicomponent fibers in the range

of 2–4 denier are spun after which the fibers are split into microfibers. If a 32-segment pie of nylon/

polyester fiber is used, the final denier is in the range of 0.1 denier. Brushing and other techniques

can be used to enhance the effects. Splittable, hollow fibers are also being used to achieve fi ber

splitting. For instance, for polyester/polypropylene fiber combinations, “natural” splitting occurs

after passage through the spinneret. After mechanical drawing, the yarn has a denier of about 0.2
well within that described for microfibers. More recently, tipped fibers are being studied. Here, a

bicomponent fi ber is made except the second polymer is placed on the tip of the fi ber. After spin-

ning, the fibers are twisted and then wet heat is applied resulting in the tips of the fi bers breaking

apart into microfibers with a denier of about 0.2 because the two different polymers have different
heats of elongation, and so on the physical changes cause the two polymer components to break
apart.
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