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Nylon 6 vs Nylon 66

 

Nylon 6 vs Nylon 66

By Kevin Chen - ENERGETIC Plastics
 
Polyamide or nylon is a semi-crystalline polymer and has been commercialised since the mid-1930s. This material offers an excellent combination of mechanical and electrical properties coupled with good resistance to heat and chemicals. It has high lubricity and moderate strength. It is tough, inexpensive, but has poor dimensional stability due to water absorption.
 


A number of different types of polyamide are available covering a wide range of properties.
 
The standard grades are PA6 and PA66. PA6 is made by hydrolytic polymerisation of caprolactam. PA66 is made by the polycondensation of hexamethylenediamine and adipic acid. Special copolyamide grades such as PA6/12 and PA6/66, partially aromatic grades and transparent grades are also produced. Polyamide 11 and polyamide 12 are high performance materials. Polyamide 11 is produced by polymerisation of amino-undecanoic acid from castor oil. PA12 is obtained from crude oil by polycondensation of lauryllactam.
 
There are mainly two ways to synthesis Polyamide. Dual numbers of the polyamide (PAxx) arise from the first, a condensation reaction between diamines and dibasic acids produces a polyamide salt. The first number of the polyamide type represents for the number of carbon atoms in the diamine, the second means the quantity in the acid (e.g., polyamide 612 or polyamide 66).
 
The second method involves opening up a monomer with both amine and acid groups (known as a lactam ring). The identity of the polyamide is based on the number of atoms in the lactam monomer (e.g., polyamide 6 or polyamide 12, etc.).
 
The key performance properties of PA6 and PA66 are summarized below.
 
•      Good rigidity and hardness
•      Very high strength and toughness
•      Good low-temperature impact strength
•      High dynamic strength
•      Abrasion and wear resistance
•      High heat resistance (PA6 short-term to 200 °C, long-term from 80 to 150 °C, PA66 short-term to 250 °C, long-term from 80 to 150 °C)
•      Resistant to many chemicals
•      Excellent processing properties
•      Tensile modulus: 450 to 15,000 MPa for PA6 and 900 to 15,000 MPa for PA66
•      Good mechanical and electrical properties
•      Very good abrasion and wear resistance
 


The main advantage of polyamide 6 over 66 is that it is easier to process and produces lower mould shrinkage. The main disadvantage of polyamide 6 is that it has lower strength, stiffness and abrasion resistance than polyamide 66 and higher water absorption.
 
The main advantages of polyamide 66 are its better low temperature toughness than acetal, PBT and polyamide 6, and its good fatigue resistance. It should however be noted that the choice between polyamide 6 and 66 is often made for reasons of availability, price or familiarity, rather than for technical reasons. The exception to this is ease of moulding, where polyamide 6 dominates.