Polyamides or nylons are an engineered thermoplastics with high performance and efficiency. Polyamides contain amide bonds (CO-NH) that form their repeating units. Polyamides or nylons are produced by the condensation reaction of a diacid with a diamine. This reaction is carried out by open ring polymerization of 6, 11, or 12 carbon atoms. types of polyamides, due to their hard production process and high properties, have a higher price than most polymers. In this PETROPROVIDERS article, we explain in detail the polyamides (nylon) and their types, properties, and characteristics of each polyamide, applications, and process conditions of polyamides.

Types of polyamide (nylon), features, and differences

Types of nylon

Types of nylon

Polyamide monomers can be aliphatic, semi-aromatic, or aromatic. They can also be amorphous, semi-crystalline, or with varying degrees of crystallinity. The monomers that make up the various polyamides will be described in detail in the next section.

There are several types of polyamides in this large polymer family. Two important types of polyamides that are more widely used than others are polyamide 6 and polyamide 66, which are used in industries such as fibers (textiles) and packaging. In the following, we will introduce the types of polyamides.

Polyamide 6 and polyamide 66:

Polyamide 6 or nylon 6, also known as polycaprolactam, is one of the most widely used types of polyamide. It is synthesized from a caprolactam monomer and has a melting point of about 223 ° C. The following figure shows the structure of polyamide 6.

PA 6,66 structure

PA 6,66 structure

Polyamide 66 is one of the most popular thermoplastics in the metal replacement industry. Polyamide 66 is made from the polymerization of hexamethylenediamine and adipic acid (two monomers containing 6 carbons) and has a melting point of about 255 ° C.

Main properties of polyamides 6 and 66 (PA6, PA66)

  • High strength and hardness at high temperatures
  • Good impact resistance even at low temperatures
  • Very good flowability for the process
  • Good abrasion resistance
  • Good weather resistance
  • Good fatigue resistance
  • Excellent oil and fuel resistance
  • Good electrical insulation properties
  • High water absorption
  • Low dimensional stability
  • Weak against mineral acids and polar solvents
  • Needs drying before the process

Polyamide 6 has a lower viscosity than PA66; For this reason, it has better processability and its surface molding is better. Both PA6 and PA66 polymers have many applications in the industry. Although they have almost the same properties, there is a slight difference in their structure. PA6 has lower temperature resistance and is also cheaper.

PA66 compared to PA6:

  1. It absorbs less moisture
  2. It has a higher modulus
  3. It has a better short-term thermal resistance
  4. It has a higher melting point

Applications of different types of polyamides (PA6 and PA66):

  • Automotive: Metal substitutes, applications in areas where thermal and chemical resistance are important, weight loss
  • Electronics industry: in the manufacture of meters
  • Consumer products: due to moldability, good processability, paintability, and excellent mechanical properties
  • Packaging: High perforation resistance, resistance to oxygen penetration, carbon dioxide, transparency, etc. Application in single and multi-layer packaging
  • Furniture industry, sports, etc…

Conditions of PA6 and PA66 polyamide forming process:

Injection molding:

  • Before injection, PA6 and PA66 need to be dried and the humidity reduced to below 0.2%. The injection temperature of polyamide is 80 to 100 degrees.
  • Recommended L / D 18 to 22
  • Melt temperature 270-240 degrees Celsius
  • Mold temperature 80-55 degrees Celsius

Extrusion molding:

  • Use only high viscosity grades
  • Need to dry and reduce humidity below 0.2%. Temperatures of 80 to 100 degrees are recommended.
  • A three-zone extruder with a 20 to 30 degree L / D is recommended
  • Extruder temperature for PA6: 240-270 degrees Celsius
  • Extruder temperature for PA66: 270-290 ° C

Types of polyamides; Polyamide 11 (PA11 and PA12)

Nylon 11 or PA11 is an engineered, bio-based plastic made from renewable sources (castor plant) and produced by the polymerization of amino decanoic acid. Polyamide 11 is one of the first bio-based polymers with a melting point of about 190 degrees Celsius.

Several properties of PA11 are similar to PA12 but it performs better in thermal and UV resistance. It also has less water absorption. PA11 shows good dimensional stability and impact resistance.

Polyamide 12 is a semi-crystalline thermoplastic that has a function similar to PA11. This polymer is also expensive compared to other types of polyamides. You can see the structure of PA12 in the figure below.

PA 12 structure

PA 12 structure

Key properties of PA12

  • Lower impact resistance
  • High UV resistance and abrasion
  • It has less water absorption than PA6, PA66, and other types of polyamides.
  • Appropriate dimensional stability
  • It has transparent and flexible grades
  • This polymer is used in various industries. For example automobiles, sports equipment, protective layers of some pipes, pneumatic hoses, and hammers.

PA11 and PA12 forming process

Injection molding:

  • Need to dry before the process, 6-12 hours at a temperature of 80-90 degrees Celsius (humidity reduction below 0.1%)
  • Three-zone extruder with L / D 18-22
  • Melt temperature 180 to 230 degrees Celsius
  • Mold temperature 30 to 100 degrees Celsius

Extrusion:

  1. Need to dry before the process, 6-12 hours at a temperature of 80-90 degrees Celsius (humidity reduction below 0.1%)
  2. The temperature of the first area of ​​the extruder is approximately 200 degrees Celsius
  3. Three-zone extruder with L / D at least 24
  4. Cooling of the feeding area is needed
  5. Shear elements are recommended

Polyamide 610 (PA610)

PA610 polymer is a semi-crystalline polyamide that is produced by polymerizing the monomers mentioned in the table at the beginning of the article. The approximate melting point of this polymer is 223 degrees Celsius.

Key properties of PA610:

  • Less water absorption than PA6 and PA66
  • Lower brittleness temperature than PA66 and PA6
  • Good abrasion and chemical resistance
  • It needs a lot of drying before the process
  • It is stronger than PA11, PA12, PA612 in terms of mechanical properties.
  • It has a low coefficient of friction
  • Suitable electrical insulation properties
  • It has high shrinkage
  • It has a high price
  • It has a weak resistance to strong mineral acids

PA610 polymer is widely used in the manufacture of insulation in the electronic industry due to its insulating properties, thermal resistance, and flame retardancy.

A summary of the study of different types of polyamides and their applications

In this article, we saw the types of polyamides and their applications and properties. In general, polyamide is a type of polymer that has suitable properties for the production of plastics and various materials in the industry.

The degree of crystallinity has a significant effect on the melting range of crystals and moisture absorption by polyamides. Increasing the percentage of crystallinity increases the chemical resistance to acid and base, strength and abrasion resistance, the amount of yield point stress.

In addition, it increases the melting temperature and the application temperature range and reduces the insulation properties, elongation, dielectric coefficient, transparency (opacity), and the tendency to absorb moisture (due to the reduction of voids between the amide chains).

The main focus of the global polyamide trade, which began 80 years ago, was mainly on PA6 and PA66. Due to the many applications, these two polyamides account for about 90% of polyamide production.

Global trade in the two polymers was $ 24.4 billion in 2014, and forecasts and forecasts suggest an increase of $ 31.2 billion by 2022. In 2013, the global demand for polyamides was about 7 million tons, which increased by approximately 4.3% in 2016 to 7.3 million tons.


Are Polyamides Good to Use?

Yes! These materials have high strength and are resistant to pressure and impact. In addition, they can be used to produce durable plastics in the industry.

Is polyamide better or linen?

These two substances have almost the same raw materials, But polyamide is much cheaper.

Is polyamide plastic?

Yes! Polyamides are one of the most important plastics in the global industry.

Are all types of polyamides harmful to human health?

This substance is used in various industries and recent years, studies have shown that it does not pose a serious risk to human health.