Introduction
Nylon is the most useful synthetic material globally. We depend on nylon every day for a variety of reasons. A stretchy clothing item like tights or stockings probably has nylon on the label.
You can find nylon in toothbrush bristles, umbrellas, knits, swimwear, activewear, underwear and hosiery. You could use a nylon parachute to land safely after jumping from an aeroplane! But you rarely know how nylon is made, even though you interact daily.
Discover the manufacturing process of nylon in this article.
Did You Know? In 1935, Wallace Hume Carothers synthesised nylon 66 at DuPont's Experimental Station, at DuPont's research facility.
An Overview of Nylon's History
The invention of nylon marked the beginning of the synthetic age as it was the first fabric made entirely in laboratories.
Around World War II, nylon became readily available to the general public. During wartime, nylon played two crucial roles.
Nylon's strength and durability made it an excellent material for military products such as parachutes, ropes, tents, and tyres.
Additionally, as silk imports from Asia faced severe shortages and price fluctuations, nylon replaced everything made from silk, including silk stockings.
What Is Nylon?
Polymers, such as nylon, are plastics made up of long, heavy molecules with short, ever-repeating sections of atoms, like heavy metal chains. Nylon refers to a whole family of similar materials called polyamides rather than a single substance.
The first synthetic fibre was nylon. Dupont established a fundamental research program in 1928. Any discovery would benefit the company - as a means of diversifying its business.
After removing a glass rod from a polyester still, a solid filament was observed adhering to the solution.
No matter how far you stretch the filament, it will never return to its initial length. As a result, the group decided to focus on textile fibres. It was called the miracle fibre for several years, and the term nylon was chosen to describe it.
The first nylon was called type 6,6. This type of nylon is made from two chemicals containing six carbon atoms. Types 6 and 10 of nylon were also developed simultaneously, with one chemical having six carbon atoms per molecule and the other having ten carbon atoms per molecule.
Apparel and home furnishings made from nylon 6 and 6 were considered desirable; nylon 10 is used to make brushes and other items. Polyamide is the name given to nylon in many countries.
Read More: How Is Rubber Manufactured for Industrial Use?
Properties of Nylon
Several commercial applications for nylon polymers include fabrics, fibres, shapes, and films.
Nylon's lustrousness, damage resistance, elasticity, strength, moisture resistance, and quick-drying properties are listed below.
Nylon’s Strength and Elasticity
The nylon polymer is generally a firm, tough, and durable thermoplastic (which melts and turns runny when heated to approximately 260°C or 500°F). It is elastic because it is an amorphous solid or viscous fluid at temperatures above its melting point.
Lustrousness of Nylon
Nylon has a lustrous finish, which means it shines. As a result of its various uses, plastic can be gleaming, semi-lustrous, or dull in appearance. Therefore, it is often used as a fabric.
Moisture Resistance
Despite being synthetic, it is highly immune to attacks from natural nasties like moulds, insects, and fungi. It is also reasonably resistant to wear and weathering.
Quick-Drying Polymer
The outer surface of this fabric cannot easily be penetrated by water molecules (unlike natural fabrics like cotton or wool), so it is waterproof and fast-drying. Due to its ability to absorb water, it is less prevalent in swimwear than synthetics that dry faster.
Damage Resistance
Besides phenols, acids, and other harsh chemicals, nylon is reasonably resistant to several everyday substances.
Nylon Manufacturing Process
Nylon fibre is produced by carefully and slowly mixing diamine and dicarboxylic acids. Listed below are the steps involved in the nylon manufacturing process.
Step 1: Diamine Acid Extraction
Nylon fabrics are polymers, making them from carbon-based molecules called monomers. Nylon is a material that comes in a variety of types. Still, most are formed from a polyamide monomer extracted from crude oil, also known as petroleum.
During nylon manufacture, a monomer called hexamethylenediamine is frequently used, sometimes called diamine acid. Using these oil remains for other purposes or discarding them is possible. Crude oil is used to extract this monomer.
Step 2: Combining and Heating
Adipic acid and diamine acid are forced to react to make nylon a polymer. Nylon fabric was first made from this type of polymer, called PA 6,6. PA 6,6 is transformed into a molten substance from its crystallised form when heated.
Step 3: Extrusion and Loading
A spinneret, a device with dozens of tiny holes resembling a showerhead, is used to extrude this substance. Nylon extrusion through the spinneret immediately hardens, and the resulting fibres are ready for loading.
Read More: How Are Decorative Laminates Made?
Step 4: Stretching
"Drawing" is winding these fibres onto another spool to increase their strength and elasticity after stretching. After the parallel arrangement of polymer-structured molecules has been completed, the fibres are ready to be spun into clothing or other forms of fibre.
Step 5: Drawing and Spinning
Filaments are drawn four to five times their original length during the drawing process. As a result, macromolecules align themselves most efficiently. The orientation of the highest parallelism determines yarn tensile strength and tenacity.
Drawing of filaments happens between the different duos on heated rotating cylinders known as godets during the drawing process.
Continuous air jets mix the filaments (usually between 140 and 280) after drawing. When the filaments are intertwined, they tangle together, allowing the customer to work efficiently with the yarn.
Spools are wound directly with the finished yarn. Spools of thread of this size weigh approximately 9.0 kg. Winding speeds range from 2000 to 4000 metres per minute during spin-draw. A new bobbin can be wound in seconds from an empty tube to a full one using automatic winders.
Continuous spinning is the nylon-making process, and there are no interruptions in nylon production assembly.
Nylon 6 Manufacturing Process
There are six carbon atoms in Caprolactum, which is the main component of nylon 6. As well as having high tensile strength, nylon's six fibres have elasticity and lustre.
Besides being wrinkle-proof, they are also highly resistant to friction and chemicals such as alkalis and acids. The fibres can absorb as much as 2.4% of water, but their tensile strength is affected.
There is a 47 °C glass transition temperature in nylon 6. The Nylon 6 manufacturing process consists of the following steps:
1. Polymerisation
Caprolactam has six carbon atoms and is converted into nylon 6 by "ring-opening polymerisation.” After heating caprolactam to about 533 Kelvin for 4-5 hours, the ring begins to break in an inert nitrogen atmosphere.
Hydrolysis is the process by which the ring opens. The molecular chains continue to grow in a nitrogen atmosphere at low pressure. From a fluid to a honey-like viscosity, caprolactam changes. This results in a hot molten polymer.
2. Quenching in Water
As the polymer is pressed through a type of spinneret, it cools down and forms a solid shape, forming a strand. Granules of nylon 6 are manufactured by cutting polymer strands in a granule-making machine. Here is the chemical equation for the whole reaction:
3. Melt-spinning
Nylon 6 is spun using a "melt spinning" process. As part of this process, the polymer is melted under the exclusion of air at a temperature of 250°C-270°C ( 30°C-50°C above its melting point). An extruder melts polymer homogeneously.
Feeding pumps and extruders feed hot and molten polymer to spinnerets. A tiny hole in a spinneret transmits molten polymer. In this way, a nylon 6 filament is formed. The filaments are entered into the quench duct at the lower end of the spinneret.
Air is used to quench still-hot filaments for 2-4 metres. If you want to avoid the filaments sticking together, it is essential to maintain a gentle and stable airflow.
4. Drawing
Drawing involves drawing filaments four to five times their original length. During the drawing process, the filaments are drawn between different pairs of duos by rotating cylinders called godets which run at different speeds.
After the filaments are drawn, a continuous air jet is applied to them (generally between 140 and 280). Creating a tangle between the filaments allows the customer to handle the yarn easily due to the intermingling of the fibres.
Spools are wound directly with the finished yarn. Nylon 6 is spun continuously. Assemblies run without interruption.
Nylon 6 has certain advantages over nylon 6,6. Compared to Hexamethylene Diamine and Adipic Acid, caprolactam is easier to synthesise. Therefore, making nylon 6 is cheaper than making nylon 6,6. Moreover, nylon 6 is more tolerant of acid dyes than nylon 6,6.
Conclusion
Plastics derived from crude oil are called nylon. After an intensive chemical process, this plastic becomes the strong, stretchy fabric called nylon. The method includes the polymerisation of caprolactam and hydrolysis, water quenching through a type of spinneret, melting using an extruder, drawing the filaments and spinning it continuously to get nylon. It is then pressed into bales covered with polyethylene to produce nylon fibres.
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