Polyamide: Definition, Composition, Types, Properties, and Applications

Polyamide is a high-performance synthetic plastic, composed of a long polymer chain bonded by amide groups. The specific composition and properties of polyamide vary depending on whether it is an aliphatic, aromatic, or semi-aromatic polyamide. Polyamides are all known for their high strength, durability, chemical resistance, and low cost. The high performance and low cost of polyamide lead to applications in the textile, engineering, automotive, electrical, and 3D printing industries.

This article will discuss polyamide’s definition, composition, types, properties, and applications. 

What Is Polyamide?

Polyamide is a term used to describe a synthetically produced polymer that uses an amide group to connect the repeating units within its molecular chain. Two popular types of polyamide are nylon and aramid (better known by its trade name Kevlar®).

What Is the History of Polyamide?

Polyamide is a synthetic material that was first produced in the 1930s. It was discovered by Wallace H. Carothers and his research team in 1931 while working for DuPont in America. However, it wasn't until 1938 that polyamide was commercially produced. By 1941, nylon (a specific form of polyamide) was used to produce stockings, an application which it still holds today. The plant used to produce nylon for various applications, including stockings, is located in Seaford, Delaware. 

What Is Polyamide Made Of?

Natural polyamides are formed of amino acids, but polyamides are also synthetically produced using petroleum, which is much cheaper. The definition of polyamide is plastic with long, repeating molecular chains which are bound together by the use of amide bonds. 

How Are Polyamides Made?

Although polyamides do occur naturally, they are produced synthetically with the use of crude oil. The monomer diamine (hexamethylenediamine) is mixed with adipic acid in the production of the most popular polyamide, nylon 6,6. When these two chemicals react, the diamine produces a repeating monomer chain referred to as a polymer. This newly formed polymer is produced in the form of salt, which is then heated to a molten state. The now molten polymer is extruded through a spinneret that cools the molten polymer as it passes through, producing a fiber. This fiber is then wound onto a bobbin prior to being woven into a fabric. 

What Are the Characteristics of Polyamide?

Polyamides are high-performing polymers that have great strength and wear resistance when compared to other polymers. Other notable characteristics of polyamides are:

1. Very good chemical resistance.
2. High tensile strength. 
3. Good flexibility.
4. Low creep.
5. High impact resistance. 
6. Prone to being hygroscopic.

What Is the Color of Polyamide?

Polyamides can come in various colors including: yellow, white, and light brown. However, polyamide fibers can be dyed to any color, and solid polyamides can be surface finished with a wide variety of paint colors. 

What Does a Polyamide Look Like?

Polyamide’s appearance will vary greatly depending on how it is dyed or painted and whether it comes in woven fabric or solid form. Figure 1 below is a photo of a 3D-printed polyamide part which is black and appears to be hard and rough:

The rough surface finish is a product of the 3D printing process. If a polyamide is extruded into a solid it will be a lot smoother and could be a different color. 

While nylon stockings are also black (as seen in Figure 2), the material may also appear a lot weaker and more flexible. This is due to its thickness even though the stockings may have the same material properties as the 3D-printed polyamide. 

What Are the Different Types of Polyamide?

The three main categories of polyamide are described below:

1. Aliphatic Polyamide

Aliphatic polyamides have no double or triple carbon-carbon bonds, as opposed to aromatic polyamides that do. Aliphatic polyamides have high strength, chemical resistance, high flexibility, low creep, and a low coefficient of friction due to self-lubricating properties. Aliphatic polyamides are moderately crystalline when injection molded and their crystallinity can be increased in fiber applications. Two forms of aliphatic polyamides are nylon 6, and PA 66. These polyamides are used in machine parts, bearings, gears, conveyor belts, and electrical insulating elements.

2. Aromatic Polyamide

Aromatic polyamides are also known as aramid or by the trade name Kevlar®. Aromatic polyamides have a much higher strength, chemical, and heat resistance, and better dimensional stability than aliphatic polyamides. The chemical composition of aromatic polyamides is much stronger. The most well-known aromatic polyamide is aramid (Kevlar®) which is used to make composite material for helmets, bulletproof vests, reinforced plastic piping, and jet engine inlets.

3. Semi-Aromathic Polyamide

Semi-aromatic polyamides are thermoplastics with a semi-crystalline structure. The combination of aliphatic and aromatic polyamides creates a polyamide that is much more water resistant and therefore much more stable. Semi-aromatic polyamides also have low creep and excellent chemical resistance. They have a mostly crystalline structure. Two examples of semi-aromatic polyamide are poly(hexamethylene terephthalamide) and poly(hexamethylene isophthalamide). Due to their chemical resistance, semi-aromatic polyamides are used in fuel lines, coolant pumps, aircraft engines, fuel cut-off valves, and headlight components. 

What Are the Properties of Polyamide?

There are many types of polyamide, and all of the aliphatic polyamides are denoted using two numbers. Each number represents the number of carbon atoms in the monomer of the diamine and dibasic acid used to create the polyamide respectively. Below is a table noting the properties and applications of different polyamides:

What Are the Physical Properties of Polyamide?

The most notable physical property of polyamide is its excellent wear resistance due to its low coefficient of friction created by its self-lubricating properties. Below is a list of other physical polyamide properties:

1. Low density.
2. Temperature resistance.
3. Good impact resistance.
4. High strength.
5. Flexibility. 

What Are the Chemical Properties of Polyamide?

The chemical property that makes polyamides stand out from other plastics is its excellent chemical resistance. Other chemical properties of polyamides are listed below:

1. Very susceptible to osmosis. 
2. Nontoxic. 
3. Chemically stable. 
4. Nonflammable. 

What Are the Applications of Polyamide?

The various applications of polyamides are discussed below:

1. Textiles and Fibers

Textiles and fibers are one of the first applications of polyamides. Fibers are long, thin extrusions of polyamide which can then be woven into a textile for clothing, bedding, upholstery, curtains, and carpets. The main benefits and reasons for using polyamides in textiles are they are cheap, wear-resistant, flexible, and strong. 

2. Engineering Plastics

Engineering plastics are broadly defined as plastics that have better-performing properties than more widely used plastics. In the case of polyamides, these properties are good wear resistance, high strength, chemical resistance, and impact resistance. These better properties mean polyamides are used for helmets, bearings, supports, piping, and protective equipment. 

3. Automotive Industry

Polyamides are used in the automotive industry for their light weight, low cost, and good mechanical properties. Specific automotive applications include engine air intakes, engine covers, pulley tensioners, fuel lines, fuel pumps, lights, and vehicle trim. 

4. Electrical and Electronics

For a long time, polyamides have been the material of choice for electrical connectors. This is because electrical connectors, as well as other non-conductive electrical parts, require high heat resistance which polyamide can offer. Polyamide is also chosen due to its low cost, easy formability, high strength, and electrical insulation properties. 

5. Filaments for 3D Printing

A polyamide 3D printing filament takes the form of a spooled wire which is fed into a 3D printer to be processed into a part. The polyamide filament then melts and turns into a liquid state which is then extruded out of the printhead and solidified on the print bed. As with other applications, polyamide is used as it is cost-effective and has mechanical properties that stand out compared to other polymers used in 3D printing. For more information, see our guide on Filaments for 3D Printing.

What Are the Benefits of Polyamide?

The main benefits of using polyamide are its low cost combined with its desirable mechanical and chemical properties. The beneficial properties are listed below:

1. Chemical resistance.
2. High strength.
3. Elasticity. 
4. Durability. 
5. Abrasion resistance.
6. Temperature resistance.

What Are the Limitations of Polyamide?

There are limitations to using polyamide for certain applications which are listed below:

1. Susceptible to water absorption.
2. Susceptible to UV degradation.
3. High shrinkage when cooling during manufacture. 
4. Electrically insulative.
5. Unsustainable. 

Why Use Polyamide?

The reason behind choosing polyamide over other materials will vary for different applications. When using polyamide for electrical cable protection, it offers better performance, flexibility, and impact resistance than PVC protection. In the automotive industry, it is used because it is cheaper and lighter than metal. In machines, it is used over other materials due to its high flexibility and durability. 

Is Polyamide a Good Fabric?

Yes, polyamide can be used to make good fabric for specific applications due to its high durability and flexibility. Polyamide fabrics also benefit from being waterproof and quick drying as the fibers don't hold water the same way natural fibers do. Finally, polyamide fabrics are easy to dye any color making them aesthetically pleasing.

Are Polyester and Polyamide the Same Thing?

No, polyester and polyamide are not the same things although they both share similarities and differences. For example, polyamides are only thermoplastic, whereas polyester can be thermoplastic or thermoset. Polyamide is a more durable material and is better at blocking UV rays. In the textile industry, polyamide is used for outer garments, whereas polyester is lighter, which leads to it being used for garments that need to be permeable. For more information, see our guide on the Description of Polyester.

Is Polyamide a Synthetic Polymer?

Yes, polyamide is a synthetic polymer. While polyamides do occur naturally, they are mostly produced using crude oil. The oil-derived materials are synthesized to mimic the chemical composition of the naturally occurring material. 

Is Polyamide Commonly Used in 3D Printing?

Yes, polyamide is commonly used in 3D printing as it has desirable mechanical properties for a relatively low cost. Additionally, a lot of 3D printing is still printed in polymers due to cost, which means that polyamide is even more desirable when the only other option is other plastics. For more information, see our guide on Everything About 3D Printing.

Is Polyamide Plastic?

Yes, polyamide is a plastic. Polyamide is synthesized from a monomer which is then chemically reacted to form a long polymer chain. It is this long molecular chain bonded together by amides that makes polyamide a plastic. 

What Is the Difference Between Polyamide and Nylon?

Nylon is a subcategory of polyamide which means all nylon is a polyamide but not all polyamide is nylon. Nylon comes under the aliphatic category of polyamide. When compared to aromatic and semi-aromatic polyamide, nylon is cheaper and easier to produce. However, aromatic polyamide has better strength and thermal resistance which lends itself to being made into fibers. For more information, see our guide on the Differences Between Polyamide and Nylon.

Summary

This article presented polyamide, explained it, and discussed its composition and types. To learn more about polyamide, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

Copyright and Trademark Notices

1. KEVLAR® is a trademark of E. I. DuPont de Nemours and Company

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