Polyamide Fiber
The polyamide fibers include the nylons and the Aramid
fibers. Both fiber types are formed from polymers of long-chain polyamides.
Synthetic man-made account for the largest part of the raw
material used in manufacturing nonwoven bonded fabrics. In this group of
synthetic nonwoven bonded fabrics, polyamide fibers are the not only the oldest
ones used in production, they also increase the serviceability of the product.
This improved quality is of importance for various purposes, e.g.:
- where nonwoven bonded fabrics are subjected to frequent folding, as in the case of paper reinforced with synthetic fibers
- where exceptional resistance to abrasion is required, as is the case with needled floor coverings
The polyamide fibers include the nylons and the
aramid fibers. Both fiber types are formed from polymers of long-chain
polyamides. The nylons generally are tough, strong, durable fibers useful in a
wide range of textile applications.
The fully aromatic aramid fibers have
high-temperature resistance, exceptionally high strength, and dimensional
stability.
The number of carbon atoms in each monomer or
comonomer unit is commonly designated for the nylons. Therefore the nylon with
six carbon atoms in the repeating unit would be nylon 6 and the nylon with 6
carbons in each of the monomer units would be nylon 6,6.
A group of fully synthetic fiber materials, which
are manufactured in a melt spinning process. Characteristics: highly elastic,
tear and abrasion-free, low humidity absorption capability, fast drying, no
loss of solidity in a wet condition, crease-free, rot and seawater proof.
Application: fine stockings (for example nylon),
outer sporting and motorcycle garments (for example Tactel, Cordura), female
underclothes (for example Perlon), parachutes.
In the middle of the 1930s nylon, a polyamide was
brought to the market by the American chemical company DuPont. It was the first
material fully obtained from basic chemical elements. A sure sign for the
economic breakthrough of synthetic fine chemical fibers was the triumph of
nylon stockings at the beginning of the 1950s.
The textile industry concentrated above all on space
research and during the years of the Cold War on equipment for soldiers. At the
end of this, the industry had to look for new sales markets.
During the last ten years, a series of new synthetic
textiles and techniques for processing textiles have been developed, in which
war and space technology has been matched with innovative novelties from design
laboratories. A milestone: the active breathing microfibers (such as Gore-Tex).
The two main types of fiber are polyamide 6, usually known as Perlon, and polyamide 6.6, which is generally called Nylon to distinguish it from Perlon. The number or numbers after the word ‘polyamide’ indicate how many carbon atoms there are in each molecule making up the polyamide. The fact that there is only one number in one instance and two in the other shows that polyamide 6 contains only one basic module and polyamide 6.6 contains two, with six carbon atoms in each molecule.
Nylon 6 and 6.6
Polyamide 6 is made from caprolactam and polyamide 6.6 from hexamethylenediamine and adipic acid. For fiber production, the resulting polyamide has to have the capacity to be spun into filaments, i.e.
·
it must have the capacity to be melted without decomposing and
to be forced through a jet.
·
the molten mass must be such that the filaments that are still
ductile when formed do not break during cooling. Certain conditions must be
met, one of them being a minimum prescribed length for the macromolecule.
These nylon polymers
form strong, tough, and durable fibers useful in a wide variety of textile applications.
The major differences in the fibers are that nylon 6,6 dyes lighter, has a
higher melting point, and a slightly harsher hand than nylon 6
Aramid Fibers
The aramid polyamide fibers are formed from a long chain of
synthetic polyamides in which at least 85% of the amide linkages are attached
to aromatic rings. These essentially fully aromatic polyamides are
characteristically high melting and have excellent property retention at high temperatures
and excellent durability. They are unaffected by moisture and most chemicals
and are inherently flame retardant. The fibers have high strength and can be
used in a number of unique high-strength applications.
Common trade names for aramid fibers include Nomex and
Kevlar (DuPont). Aramid fibers are extremely strong and heat resistant. Fabrics
from the aramids have a high luster with a fair hand and adequate draping
properties.
The fibers are light yellow unless bleached and exhibit
moderate moisture absorption characteristics. The fibers recover readily from
stretching and bending deformation and are extremely abrasion resistant. They
do tend to pill due to the high strength of the fiber.
Other Polyamides
Several other polyamides have been introduced for use as
fibers in specialty applications where certain combinations of properties are
desired. The major specialty nylons include Qiana, nylon 4, nylon 11, nylon
6,10, and biconstituent nylon-polyester.
Manufacturing of
Polyamide Filaments
The molten mass is forced through the holes in the spinneret
by pressure pumps and metering pumps, after which it is pulled off in the form
of filaments. They cool rapidly in the (air) blasting chamber and are then
either baled or wound onto bobbins at a constant speed.
The macromolecules are still randomly distributed in the
filaments, which is why they are stretched so that molecules are more
longitudinally oriented.
Once they have this orientation, the filaments take on their
characteristic physical properties and can be cut to the lengths needed to make
the fibers. Then the filaments of staples are prepared to ensure that they
retain their processing properties.
