What is Polyamide (Nylon)?
Polyamides or nylon are an important class of high-performance engineering thermoplastics due to their balanced properties. Polyamides contain repeating amide bonds, i.e. -CO-NH-. Nylon was discovered by Wallace Hume Carothers, a chemist hired by DuPont de Nemours in 1928 to lead an extensive research program to develop new polymeric materials. In 1935, he developed the formula known as PA 66:
Polyamides are characterized by high temperature and electrical resistance. They also exhibit excellent chemical resistance thanks to their crystalline structure. They have excellent mechanical and barrier properties. In addition, these materials are highly flame retardant. When reinforced with glass fibers (short or long), the strength of their structure can compete with that of metals, which is why polyamides are often used as metal substitutes.
All polyamides tend to absorb moisture because of the amide chemical group. Moisture acts as a plasticizer in polyamides, reducing tensile modulus and increasing impact strength and flexibility. Moisture absorption also has a major effect on dimensional variations; this must be taken into account when designing parts.Polyamides are used in many applications, including automotive and transportation, electrical and electronics, consumer products, and many others.
Polyamide 6 (PA6) and Polyamide 66 (PA66)
Polyamide 6 (PA6) is also known as nylon 6 or polycaprolactam. It is one of the most widely used polyamides in the world. It is synthesized by ring-opening polymerization of caprolactam. The melting point of polyamide 6 is 223°C.
Polyamide 66 (PA66) or Nylon 66 is one of the most popular engineering thermoplastics and is mainly used as a replacement for metal in various applications. Nylon 66 is produced by polycondensation of hexamethylene diamine and adipic acid (two monomers with 6 carbon atoms each). The melting point of polyamide 66 is 255°C.
Molecular Structures of Polyamide 6 (top) and Polyamide 66 (bottom)
Main Properties of PA6 and PA 66
PA6 and PA66 are by far the most widely used polyamides in the world. Both polyamide 6 (PA6) and polyamide 66 (PA66) are used in many different markets and applications due to their excellent performance/cost ratio. Their key properties are listed below.
- Excellent strength and stiffness at high temperatures
- Good impact strength, also at low temperatures
- Very good flowability for easier processing
- Good abrasion and wear resistance
- Good fuel and oil resistance
- Good fatigue resistance
- PA 6 has an excellent surface appearance and better processability than PA66 (due to its very low viscosity)
- Good electrical insulation properties
- High water absorption and water equilibrium content limit its use
- Low dimensional stability
- Attacked by strong mineral acids and absorbs polar solvents
- Proper drying before processing is required
Although they have a similar set of properties, there are still slight differences. PA6 has slightly lower temperature resistance than PA66 and is also slightly less ductile. Compared to PA6, PA66 has the following characteristics:
- A slightly lower moisture absorption capacity
- Higher modulus
- Better wear resistance
- Better short-term heat resistance
PA6 and PA66 have similar properties and are indistinguishable to the naked eye. NIRLAB Polymers supports the accurate differentiation between polyamide 6 (PA6) and polyamide 6.6 (PA66).