Fibers created
through technology either from natural materials or from chemicals.
MOST MANUFACTURED
FIBERS ARE THERMOPLASTIC
which means they soften and melt in the presence of heat and reconstitute
when
the temperature
is lowered below the glass transition temperature.
The production and use of manufactured fibers has increased in the last 20 years. As you can see in the graph below, the production of cellulosics has decresed while the production of manufactured fibers, particularly polyester, nylon, and olefin has increased.
Fibers are formed
from liquid polymers. The liquid polymers are extruded through a
spinneret
(see Figures 6.1, on
page 127; 6.2, 6.3 on page 128). A spinneret
has a design similar a shower head with holes. Each hole produces
one
fiber.
Spinneret
Fibers being extruded
The fibers become
solid after being extruded by contact with air currents (called melt
spinning) or solvents (dry
spinning or wet spinning).
Most fibers are round but can be made into various shapes by varying the
shape of the hole in the spinneret.
Fiber size.
Fibers size is designated as denier. This designates the
size or fineness.The denier is related to the end use of the fiber.
One of the recent technological advances in fibers has been the development
of microfibers. Microfibers have a denier less than
1. These fibers have been used for lightweight, soft fabrics.
The following diagram is a comparison of microfibers with flax, wool,
cotton, and silk.
Newly formed filaments have amorphous
and crystalline areas. The filaments are often subjected to drawing
to
orient them into a more crystalline
arrangement (refer to your notes from Chapter 3).
General properties of manufactured fibers: (exceptions will be noted in individual fiber discussions).
1. stronger
than natural fibers
2. resilient
3. thermoplastic
(have a melting point)
4. most
burn; when they burn, they melt & drip and produce a dark, toxic smoke;
the residue is a hard bead
5. resistant
to insects, mold, mildew
6. bacteria
will grow on the surface but not damage the fibers
7. low
specific gravity
8. resistant
to most acids and alkalis
9. hydrophobic
10. build up
static electric charges
11. dimensionally
stable
12. good
abrasion resistance
13. oleophilic
Newly formed filaments have amorphous and crystalline regions. These amorphous regions reduce the strength of the fibers; therefore, the fibers are often drawn to orient the polymers into a more crystalline arrangement (see page 134).
Bicomponent Fibers
Often more than one fiber is extruded through a spinneret. These
are called bicomponent fibers. These may be two completely different
generic polymers (such as nylon and polyester) or variations of the same
polymer (such as Nylon 6 and Nylon 6,6). they may be side-by-side
or sheath-core (see page 136).
Manufactured
(man-made) fibers are classified according to whether they have a cellulose
base or a petroleum (synthetic) base.
Factors that affect cost of natural and manufactured fibers:
Natural Manufactured
Dependent on natural elements
Dependent on people and machines
Quality can be variable
Quality can be very consistent
Often labor intensive to harvest and process
Not as labor intensive
Chapter 6: Manufactured Cellulosic Fibers
Manufactured cellulosic fibers
Rayon Rayon
Acetate Acetate
Lyocell Lyocell
Link to American Fiber Manufacturers Association (click on underline)
Manufactured (man-made) fibers are classified
according to whether they
have a cellulose
base or a synthetic base.
Manufactured cellulosic fibers
Manufactured cellulosic fibers have a cellulosic base but are regenerated cellulose - the cellulose is broken down and made into a solution which is extruded as a fiber
Properties of manufactured cellulosic fibers
1.
Low tenacity
2. Weaker when wet than when dry
3. Low abrasion resistance
4. Drycleaning often recommended
5. Burn readily, similar to cellulosic fibers
6. Poor dimensional stability
RAYON
- Wood pulp is the major source of cellulose for rayon;cotton linters can
also be used. Wood pulp or cotton linters are dissolved in chemicals
and remade as a fiber solution. The earliest process was called cupramonnium.
2. Viscose - most commonly used rayon
3. High-wet modulus -physical structure more similar to natural cellulosic
fibers. Have greater strength when
wet than viscose rayon.
4. High tenacity rayon - final spinning step is modified to increase
strength; zinc compound is added while fibers are being drawn. More
oriented and crystalline.
=Rayon is a cellulose
fiber regenerated from wood pulp; its first name was “artificial silk”
=Rayon is valued
for its excellent hand and drape
=Characteristics
of rayon are similar to cotton except that its wet strength is lower than
its dry strength
= High wet modulus
(HWM) rayon has superior properties to viscose rayon
=Rayon is used
extensively in apparel, home furnishings fabrics and nonwoven fabrics
ACETATE - first thermoplastic fiber
Acetate - Acetate is a cellulose fiber regenerated
from wood pulp or cotton linters
Fiber characteristics
are similar to rayon except that acetate is thermoplastic (will melt in
presence of
heat).
Acetate is a weak fiber; usually it should
not be laundered
Acrylic fume fades - changes color in the
environment (not necessarily related to light)
LYOCELL
Lyocell - Lyocell
is a cellulose fiber regenerated from wood pulp
Characteristics are similar to cotton and superior to rayon
Tencel by Courtaulds (now Acordis)is the most common trademark name
Lenzing also makes Tencel by Lenzing
Tencel
Manufacturing process is much more environmentally friendly than for rayon;
solvent to dissolve wood pulp is non-toxic and almost completely recycled.
Properties of manufactured synthetic fibers:
1.
Thermoplastic (heat sensitive); have a melting point
2.
Resilient
3.
Strong
4.
Burn readily unless treated, melt and drip
5.
Resistant to insects, microorganisms
6.
Resistant to mild acids and alkalis
7.
Hydrophobic
8.
Develop static electricity
9.
Oleophilic
Fiber Size
The size of fibers is expressed as denier per filament (dpf). Depending on the end use, the denier can vary greatly. Denier is the weight in grams of 9000 meters of fiber.
Microfibers are fibers less than 1 dpf and are used in applications
where lightweight fabrics are needed. Microfibers can be packed very
tightly in yarns and, therefore, make compact fabrics that resist water,
wind, and soil.
Comparison of natural fibers with microfibers.
Most manufactured fibers for general use are from 3-9 dpf.
Fiber shape:
Most manufactured fibers are round after extruded. However,
cross-sections may be varied to give the fiber unique properties.
Nylon (strong)
-As of 1997,
nylon has 61.6% of the US market share for carpet and rugs.
-Nylon is strong;
the crystalline structure and close hydrogen bonding in the fibers
provide strength.
-Nylon has excellent
compression resilience.
-Nylon has a
low specific gravity, making it possible to have a lightweight, sheer material.
-The sunlight resistance
of nylon is good but not excellent.
-For carpet applications,
the cross section of nylon is often modified to provide for soil-hiding,
reduce light reflection
Modified cross sections Trilobal
cross sections
Polyester(easy care)
-Polyester
claims approximately 42% of the U.S. apparel market and is used for home
furnishings
and industrial fabrics as well as consumer products such as sleeping bags.
In
1997, polyester
accounted for 5.9% of the U.S. carpet and rug industry.
-Easy care is
the claim to fame for polyester; most fabrics can be machine washed and
dried
- Polyester
is often blended with other fibers to offer its properties of resiliency,
easy
care,
strength, and
dimensional stability
-Polyester is
very oleophilic
-The aromatic
ring structure of polyester makes it hydrophobic (see notes taken in class)
-Polyester has
a higher specific gravity than nylon and provides less cover for the weight.
Major end uses include apparel, carpet, upholster
Olefin (low specific gravity, non-absorbent)
two types of olefin,
polypropylene and polyethylene.
-As of 1997,
olefin had 32.1% of the U.S. carpet and rug market
-Olefin is used
for carpet face as well as carpet backing.
-Olefin has
the lowest specific gravity of the fibers.
-Olefin has
a low melting point
-Olefin is non-absorbent
and usually solution dyed for color.
-Olefin has
wicking properties that make it comfortable for some apparel
Major end uses include carpet face and backing,
upholstery (usually sold under the trade name Herculon) and thermal
underwear
Acrylic(excellent
sunlight resistance)
- Acrylic has properties similar to wool including
the helical shape
-Acrylic has a much lower specific gravity
than wool; therefore, it is much lighter in weight than wool
-Acrylic can be laundered but should not be
dried in the dryer, it often gains in dimension
-Acrylic has excellent sunlight resistance
-Acrylic burns readily
Major end uses include apparel: outdoor materials
such as furniture coverings, canopies, tents, marine upholstery
Modacrylic
inherently flame
retardant;<>
Modacrylic has a low melting point
Rubber and Spandex (elasticity
and recovery)
Rubber and spandex are ELASTOMERIC fibers.
rubber can be natural or synthetic.
Natural rubber fibers are weak and have low melting
points; synthetic rubber was developed
in the 1930s and has better properties.
Spandex can be stretched up to 5 times its
length and return almost completely to its original
shape. Lycra by DuPont is a common
tradename. The spandex fiber is very amorphous in
the relaxed state; when stretched the amorphous
polymers straighten and bond with each
other thus preventing breaking under the
stress of being stretched. When the stress is
removed, the fiber returns to its original
internal structure.
Spandex has good resistance to sunlight,
body oils, chlorine water, salt water
High Performance Fibers (click here for more information)
Aramids ( NomexHigh resistance to
heat and fire
(Kevlar)High
resistance to heat and fire; strong; do not melt
PBI - (does not burn in air)
Sulfar - excellent chemical and flame resistance