Polyamide Fibers:

Polyamide substance composed of long, multiple-unit molecules in which the

repeating units in the molecular chain are linked together by amide groups.

Amide groups have the general chemical formula CO-NH. They may be produced

by the interaction of an amine (NH2) group and a carboxyl (COOH) group.

NH2+COOH CONH+H20

When 85% or more of the amide groups are linked directly to phenyl rings, the polyamide is classified as an aramid. When the rate is lower than 85%, the polymer is classified as a nylon.

Amide Linkage

Commonly Used Polyamide:

Large number of polyamide materials available to produce nylon fibers. The two most common versions are

Nylon 66 (polyhexamethylene diamide) Nylon 6 (Polycaprolactam)

(C 6H 11

NO)n

Chemical Composition of Nylon 6:

Nylon6 is made from Caprolactum which is made by a series of reactions using products obtained from coal tar.

Coal Tar--> Benzene--Chlorine--> Chlorobenzene--> Sodium Phenate--HCL--> Phenol--H2 (Nickel)-->Cyclohexanol--Oxidation Air Fe, Zn Catalyst--> Cyclohexanone-

-> Cyclohexanone Oxime--H2SO4--> Caprolactam

I am including it to show that it is possible to get a polyamide from a single monomer. called caprolactam.

Caprolectum is a white flaky solid, melting at 68 degree and is soluble in water. the polymerization is carried out in stainless steel cylinders.

Caprolactam has 6 carbon Hence “Nylon 6”. When Caprolactam is heated at 533k(500oC) in presence of nitrogen for 4-5 hours . The ring breaks and under goes polymerization.

Amide Bond within each Caprolactam molecule broken .The ring opens, and the molecules join up in a continuous chain

Polymerization of Nylon 6:

Step Growth

6 Carbons

Melt Spinning of Nylon 6:

Chemical Properties of Nylon 6:

Acids - concentrated Poor

Acids - dilute Poor

Alcohols Good

Alkalis Good-Fair

Aromatic hydrocarbons Good

Greases and Oils Good

Halogenated Hydrocarbons Good-Poor

Halogens Poor

Ketones Good

Physical Properties of Nylon 6:

Density ( g cm-3 ) 1.13Flammability HB

Limiting oxygen index ( % ) 25

Radiation resistance Fair

Refractive index 1.53

Resistance to Ultra-violet Poor

Water absorption - equilibrium ( % ) >8

Water absorption - over 24 hours ( % ) 2.7

Nylon 6,6 is made of hexamethylenediamine and adipic acid, which give nylon 6,6 a total of 12 carbon atoms, and its name Nylon 66

Hexamethylene diamine and adipic acid are combined with water in a reactor. This produces nylon salt. The nylon salt is then sent to an evaporator where excess water is removed. The nylon salt goes into a reaction vessel where a continuous polymerization process takes place.

Chemical Composition of Nylon 66:

One of the monomers is a 6 carbon acid with a -COOH group at each end - hexanedioic acid.

The other monomer is a 6 carbon chain with an amino group, -NH2, at each end. This is 1,6-diaminohexane.

When these two compounds polymerise, the amine and acid groups combine, each time with the loss of a molecule of water. This is known as condensation polymerisation.

Condensation polymerisation is the formation of a polymer involving the loss of a small molecule. In this case, the molecule is water,

keeps on happening, and so you get a chain which looks like this:

Polymerization of Nylon 66:

Melt Spinning of Nylon 66:

Chemical Properties of Nylon 66:

Property Value

Material Medium High tenacity

Density g cm-3 1.14 1.14

Extension to break % 37 14-22

Shrinkage @100C % 9 9-11

Specific Tenacity cN/tex 43 60-80

Uses of Nylons:

Synthetic replacement for silk

It replaced silk in military applications such as parachutes and flak vests, and was used in many types of vehicle tires.

Used in many applications, including fabrics, bridal veils, carpets, musical strings, and rope.

Carpets

Ropes Zip ties

Hoses

conveyor belts

Tyres

Air bags