Polyamides- Definition, Types, Properties and Applications

What are Polyamides? 

Polymers that have amide linkages are called polyamides. These are prepared by condensation polymerization of dibasic acids with diamines or their equivalents.

Polyamides occur both naturally and artificially like proteins, such as wool and silk are naturally occurring polyamides whereas nylons, aramids and sodium poly(aspartate) is artificially manufactured polyamides.

Following are some famous polyamides:

1. Nylon 6,6

Nylon 6,6 is a type of polyamide that is made of two monomers that is hexamethylenediamine and adipic acid each containing 6 carbon atoms. That's why it is called nylon 6,6.

Nylon-66-Structure

Nylon 6,6 has high mechanical strength, rigidity, and stability under heat and chemical attack. That's why it is used for making machine parts, airbags, ropes, conveyor belts, etc.

Preparation of Nylon 6,6 

It is prepared by the condensation polymerization of adipic acid and hexamethylenediamine. The acid and the amine first react to form a salt which when heated to 525 K under pressure, undergoes polymerization with the elimination of water as steam and the nylon is produced in the molten state.

Preparation-of-Nylon-66

Properties of Nylon 6, 6

1. It has a high melting point and high heat deflection temperature.

2. It offers better resistance to acids and has high stain cleanability.

3. It is more difficult to color due to dense structure with small and evenly spaced pores.

4. It exhibits greater mold shrinkage, lower expansion, and improved thermal and electrical conductivity.

Applications of Nylon 6,6

1. It is used for making swimwear, hoses, and machine parts due to its waterproof property.

2. It is also used for making glass-reinforced laminates, fasteners, and conveyor belts.

3. It is used in fibers for textiles, carpets, and molded parts.

4. It is also used for making surgical sutures and strings for musical instruments.

2. Nylon 6 or Perlon

Nylon 6 or Perlon is a polymer that was developed by Paul Schlack to reproduce the properties of Nylon 6,6. It is prepared by ring-opening polymerization of monomer caprolactam.

Nylon-6-Structure

Nylon 6 is tough, elastic, and lustrous possessing high tensile strength. That's why it is used for the manufacture of type cords, fabrics, and mountaineering ropes.

Preparation of Nylon 6

The monomer caprolactam on heating with water at high-temperature polymerization gives nylon 6. When caprolactam is heated with a trace of water, it hydrolyses to E-aminocaproic acid (6-aminohexanoic acid) which upon continued heating undergoes polymerization to give nylon-6.

Preparation-of-Nylon-6

Properties of Nylon 6

1. It has a lower melting point and lower heat deflection temperature.

2. It has a lustrous surface finish which makes it easy to color.

3. It has poor chemical resistance to acids and has a high water absorption rate.

4. It has low mold shrinkage and low stain cleanability.

Applications of Nylon 6

1. It is widely used for gears, fitting, and bearings in the automotive industry.

2. It is used as a thread in bristles of toothbrushes and strings for acoustic and classical musical instruments.

3. It is also used for manufacturing threads, ropes, filaments, and nets.

4. It is also used for the manufacturing of gun frames.

3. Kevlar

Kevlar is heat resistant and strong synthetic fiber which is an aromatic polyamide, also known as aramids. 

Kevlar-Structure

It is a polymer of 1,4-benzene-dicarboxylic acid and 1,4-diaminobenzene which have hydrogen-bonded chains, giving it a sheet-like structure.

Preparation of Kevlar

Kevlar is prepared in a solution from monomers 1,4-benzene-dicarboxylic acid and 1,4-diaminobenzene in a condensation reaction yielding HCl as a by-product.

Preparation-of-Kevlar

Properties of Kevlar

1. Kevlar is five times stronger than steel on an equal weight basis.

2. It has high heat stability and flexibility.

3. It has very high rigidity due to delocalized bonding which causes benzene rings to be inflexible.

4. There is a high electron chain density in Kevlar.

Applications of Kevlar

1. Army helmets are made of Kevlar. It is also used for lightweight bulletproof vests and high-performance skis.

2. It is used in the protective clothing worn by firefighters because it is stable at a very high temperature.

3. It is used as a protective outer shield for optical fiber cable.

4. It is widely used in the manufacturing of motorcycle helmets, car parks, brakes, clutch lining, etc.

Popular Posts

Conducting Polymers: Definition, Examples, Properties and Applications

Image
What are Conducting Polymers? As the name suggests organic polymers that conduct electricity are known as conducting polymers. They are also known as intrinsically conducting polymers (ICPs) and they have alternating single and double bonds along the polymer backbone (conjugated bonds) or that are composed of aromatic rings such as Phenylene, naphthalene, anthracene, pyrrole, and thiophene which are connected through carbon-carbon single bonds. Examples: Polyacetylene, Polypyrrole, Polyaniline, etc What is the reason behind conducting nature of these polymers? Conducting polymers comes in two forms that are doped conducting polymers and non-doped conducting polymers. The conductivity of non-doped conjugated polymers is due to the existence of a conductivity band similar to a metal. In a conjugated polymer, three of the four valence electrons form strong sigma bonds through sp² hybridization where electrons are strongly localized. The remaining unpaired electron of each carbon atom re
Read more

Crime Scene: Definition, Types and Characteristics

Image
What is a Crime Scene ? A place where the crime is committed or where the maximum physical evidence related to crime is found is known as a crime scene. A crime scene is a starting point of the investigation which provides information about the suspect and the victim. This helps to reconstruct the crime and fast resolution of the case. It is noted that the crime scene is not limited to a single place but may extend to a wider area depending upon the nature of the crime committed. For example, In a murder case where murder is done at one place and the body is disposed on another place. In this case, we have two crime scenes that give information about the crime. Types of Crime Scene Based on evidence found on the crime scene: 1. Primary Crime Scene The crime scene where the actual crime occurred or where more usable pieces of evidence were found is known as the primary crime scene. For example, A murder scene, theft, assault, etc. 2. Secondary Crime Scene The crime scene which is some
Read more

Raman Spectroscopy: Principle, Instrumentation and Applications

Image
What is Raman Spectroscopy? Raman spectroscopy was given by an Indian Physicist Sir C.V Raman , which is based on inelastic scattering of monochromatic light with the sample. The resulting light will have a different frequency than incident light due to this inelastic scattering.  This technique is widely used to analyze vibrational, rotational, and other low-frequency interactions in the molecule. This significantly helps in the elucidation of molecular structure, identifying functional groups, etc. Principle of Raman Spectroscopy Raman spectroscopy is based on the inelastic scattering of electromagnetic radiation with the molecule. We have two types of scattering that are elastic and inelastic scattering.  Elastic scattering obeys the Rayleigh law that states that there will be no loss of energy and momentum of the incidence radiation and scattered radiation. That's why this scattering is also known as Rayleigh scattering. Whereas, there will be some conditions (1 in million
Read more