Nylon is probably the most useful and versatile synthetic materials. Nylon is not only used in making fiber, technology makes it more suitable for industrial purpose also.
In this article we’ll discuss everything about nylon. Also, you will get to know about the differences between nylon 6 and nylon 66 along with its type.
Let’s dive deep………..
Table of Contents
What is Nylon?
Nylon is a long chain polymer. This polyamide fiber was the first manufactured synthetic fiber. This polymer contains lots of monomers in it.
Brief History of Nylon
In USA, DU Pont company formed a team which was led by WALLACE CATOTHERS. They were investigated if polymers could use to make useful fibers.
They synthesize polyester but found them unsuitable. Then they tried polyamides. In April 1930s, a member of CATOTHER’s team named JULIAN HILL, withdrew a glass rod he poked into a reaction mixture to find several strands of substance adhering to it. Thus they got the breakthrough.
It could be stretched to several times its original length. Again it seemed stronger to them. Again, they need 5 years to carry on their development work to make this commercially viable.
In 1938, Dr. WEST first produced “Miracle Toothbrush” using Nylon. In 1939, Nylon stockings were seen for the first time.
Most of the Nylon produced then was used in place of silk for parachute material.
Properties of Nylon
We will discuss the properties under two different sections.
Mechanical properties of Nylon
High strength to width ratio
65-85% of nylon is crystalline
Specific gravity 1.14
High breaking elongation
Excellent recovery from deformation (100% recovery, 6-8% extension)
High abrasion resistance
High flexural resistance
Melting point of Nylon 6 is 215°C
Melting point of Nylon 66 is 250°C
Tg of nylon is around 50-60°C
Other properties of Nylon
Easy to dye in comparison with polyester
Best moisture regain among synthetics (4-4.5%)
Prone to static electricity
Prone to soiling
Low resistance to sunlight
Problems with comfort like it can form tight weaves that do not “breath”
Chemistry of Nylon
Carothers set about systematically trying to create new polymer. In one series of experiments he decided to try to make synthetic polymers in which the polymer molecules were built up in a similar way to the protein chains in silk and wool.
Carothers used di-ammine and di-carboxylic acids for make nylon polymer. Both of them contained reactive groups in two places in their molecules, so they could link to-gather to form a chain.
Amines are organic compounds containing –NH2 group. When it reacts with –COOH group in carboxylic acid, -CONH amide group is formed.
In this way, nylon polymer was formed in which monomer units were linked to-gather by amide groups. One molecule of water is eliminated in this process. This process is called condensation polymerization.
Types of Nylon
There are different types of nylon. They are-
Nylon 6 – More stable than Nylon 66
Nylon 6,6 – First developed synthetic fabric
Nylon1,6 – Formed from adiponitrile, formaldehyde and water. Not commonly used in apparel
Nylon 5,10 –Specially used for industrial and scientific purpose
Nylon 4,6 – Only produced by international corporation DSM
Chemistry of Nylon 6
Nylon 6 is manufactured from only one monomer named Caprolactam. As it contains 6 carbon atom in it, thus called Nylon 6. This is made from the type ………AAAAAA……… or (A)n, where n=200
Chemistry of Nylon 66
Dupont’s version of nylon is Nylon 66. This is formed from two monomers each containing 6 carbon atoms.
The polymer can be represented as ……….ABABAB………….. or (AB)n where A and B are the parts of the molecules originating from each of the monomer.
Degree of polymerization of nylon 66 is 60-80.
How to Manufacture Nylon?
Nylon is produced in the following four ways:
Formation of polymer chips
Nylon is a polymer that is formed from monomers. The monomers are manufactured from oil based compounds. Though it’s having different types, mainly they are derived from polyamide monomer.
To form nylon hexamethylene diammine is forced to react with adipic acid at 300°C in autocalve. Often this type of nylon is called nylon 66 which is first used to make fabric. This molten polymer is then cooled under water and cut into chips.
These nylon polymer chips are called nylon salt. This molten substance are then heated and extruded through spinneret. Spinneret contains lots of tiny holes and looks like shower head.
After the extrusion, they passes through cooling chamber. Upon extrusion through the spinneret, they immediately solidifies. After cooling, the nylon filaments are dried and are conditioned in steam before winding onto bobbins. As they become hard, they can be taken up and loaded onto the bobbins.
Stretching & drawing
For improving the elasticity and strength, the stretching and drawing process is carried out. It increases the molecular orientation and makes the filaments more parallel. It also reduces the cross-sectional area. Drawn fibers are stronger and stiffer.
After the drawing process, they are completely ready to spin into yarn. Once the spinning is completed, they are ready to make the end products.
Nylon 6 is also formed in the same way as Nylon 66 is formed. But nylon 6 is formed form one monomer, caprolactam by open ring polymerization. Here is a brief discussion on it:
Nylon 6 is manufactured similarly to nylon 6.6 by heating caprolactam with a little water, a chain stopper such as acetic acid, and an acid catalyst, gradually removing the water by distillation.
The water initially hydrolyses some caprolactam to 6- aminohexanoic acid. This then reacts with caprolactam, opening the ring and generating a new amino end group.
This amino group then undergoes the same addition reaction with more caprolactam so that the forming polymer chain always has amino and carboxylate end groups.
The polyamide obtained is in equilibrium with about 10% of unreacted monomer and low molecular weight oligomers. These are removed by water washing after extrusion.
The melting point of nylon 6 is about 215 °C. Molten nylon 6 is therefore more stable than molten nylon 6.6. The lower melting temperature of nylon 6 allows filament spinning directly from the polymerization reactor without undue decomposition or changes in properties.
Nylon 6 may also be extruded as a thick band, chipped and processed as for nylon 6.6. The chips are preferred for continuous filament spinning because the denier is more uniform.
Direct spinning from the reactor is satisfactory for staple fibers where denier variations are less important because the fibers will be well-blended.
As for nylon 6.6, the conditioned filaments have a sufficiently low Tg to be cold drawn to increase the molecular orientation and crystallinity to give improved mechanical properties.
Application Area of Nylon
For Industrial Use
Automotive air bag
Industrial sewing threads
Waterproof rain wear (anoraks, cagoules)
Difference between Nylon 6 and Nylon 66
There are some technical differences between nylon 6 and nylon 66.
Melting point 215°C
Melting point 250°C
Formed from only one monomer Caprolactam
Formed from two monomers Hexamethylene di-ammnie and adipic acid
Solid nylon is used for mechanical parts such as gears and other low-to-medium stress components previously cast in metal. Engineering grade nylon is processed by extrusion, casting and injection molding. Solid nylon is used in hair combs.
Nylon is also available in glass-filled variants, which increases structure and impact strength and rigidity. Nowadays, Dupont is manufactured high performance nylon that is used in auto motive engine covers, cable insulation, electrical plastics, electrical motor insulation, 3D printing, mobile phone housing and components, sporting goods, railway technology for the long haul, transformer insulation etc.
Salma Hasin Shila, the author of this site completed her BSc. in Textile Engineering (Wet Processing Engineering) from Bangladesh University of Textiles www.butex.edu.bd (BUTEX). She has a passion for textile technology and love to write about it. She wants to share her knowledge to help the students in their studies and businessman & entrepreneurs in their business in making wise decisions fast.