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Polyamide (PA) or Nylon: Complete Guide (PA6, PA66, PA11, PA12…)

Polyamide (PA) or Nylon: Complete Guide (PA6, PA66, PA11, PA12…)

Exhibiting high temperature and electrical resistances, polyamides (nylon) are considered as high performance plastics and are widely used in automotive & transportation markets, consumer goods and electrical and electronics applications among others. Learn more about this interesting class of plastics along with the main applications and benefits of some common polyamides: PA11, PA12, PA46, PA6, PA66 and PPA (polyphthalamides). Explore more about their key properties like mechanical, thermal, electrical, etc., conditions to process this polymer and understand what makes Polyamides an ideal choice in high-end engineering applications.

Overview

What is Polyamide (Nylon)?

What is Polyamide (Nylon)?

Polyamides or Nylon is a major high performance engineering thermoplastics class because of its good balance of properties. Polyamides contain repeating amide linkages i.e. –CO-NH–. It is formed by condensing identical units, copolymers with different units.

Nylon was discovered by Wallace Hume Carothers, a chemist hired in 1928 by DuPont de Nemours to lead an extensive research program on the design of original polymeric materials. In 1935, he developed the formula known as PA 66:

Polyamide 66
Polyamide 66

Polyamides exhibit high temperature and electrical resistance. Thanks to their crystalline structure, they also show excellent chemical resistance. They have very good mechanical and barrier properties. In addition, these materials can easily be flame retarded. Polyamides became the first truly synthetic fiber to be commercialized.

When reinforced with glass fibers (short or long), their stiffness can compete with metals, this is why Polyamides are often considered in metal replacement projects. All polyamides tend to absorb moisture due to the amide chemical group. Moisture acts as a plasticizer on Polyamides thus reducing tensile modulus and increasing impact resistance & flexibility. Moisture uptake also has a huge influence on dimensional variations; this must be taken into account when designing parts.

Polyamides are widely used in markets, such as automotive and transportations, electrical and electronics, consumer goods and many more.

Different Types of Polyamides

Different Types of Polyamides

Typically, polyamides (or Nylon) are made from polycondensation of diacid with a diamine or by ring-opening polymerization of lactams with 6, 11 or 12 carbon atoms.

  • The monomers may be aliphatic, semi-aromatic or aromatic (aramids)
  • They may be amorphous, semi-crystalline and of greater or lesser crystallinity

Polyamide Monomer(s)
Polyamide 6 Caprolactum
Polyamide 12 Laurolactam
Polyamide 66 Hexamethylene Diamine/ Adipic Acid
Polyamide 69 Hexamethylene Diamine/ Azelaic Acid
Polyamide 6-10 Hexamethylene Diamine/ 1,12-Dodecanedioic Acid
Polyamide 6-12 Hexamethylene Diamine/ Sebacic Acid
Polyamide 46 1,4-Diaminobutane/ Adipic Acid
Polyamide 1212 1,12-Dodecanediamine/ 1,12-Dodecanedioic Acid
Aliphtaic Polyamide Polymers and Their Monomers

Aromatic polyamides (or Aramids) are obtained from polycondensation of terephthalic acid with diamines. PA 6-3-T is one of the common examples of aromatic polyamide which is an amorphous transparent in nature. The materials can be processed at 280-300°C. Aramids are expensive, have better dimensional stability, flame and heat resistance and higher strength as compared to aliphatic polyamides.

Among this large polymer family, several types of polyamides are particularly suited for given applications. The best choice depends on the set of performances needed as well as the economical constraints.

  • The two most widely used PA are by far PA66 and PA6. They are often extruded to manufacture fibers (textile industry) or films (packaging), or injection molded.
  • The polyamides with the highest performances are PPA and PA46, which are good candidates for metal replacement developments or very specific applications exposed to extreme conditions.
  • Bio-based PA are also available. For instance, PA11 is based on castor-oil chemistry

We will discuss some of the polyamide chemistries below.

Polyamide 6 (PA6) and Polyamide 66 (PA66)

Polyamide 6 (PA6) and Polyamide 66 (PA66)

Polyamide 6 (PA6) is also known as Nylon 6 or polycaprolactam. It is one of the most extensively used polyamides globally. It is synthesized by ring-opening polymerization of caprolactam. Melting point of polyamide 6 is 223°C.

While, Polyamide 66 (PA66) or Nylon 66 is one of the most popular engineering thermoplastics and is majorly used as a replacement to metal in various applications. Nylon 66 is synthesized by polycondensation of hexamethylenediamine and adipic acid (two monomers each containing 6 carbon atoms). Melting point of polyamide 66 is 255°C.

Polyamide 6
Polyamide 66
Molecular Structures of Polyamide 6 (top) and Polyamide 66 (bottom)


Main Properties of PA6 and PA 66


PA6 & PA66 are by far the most used polyamides globally. Both Polyamide 6 (PA6) and Polyamide 66 (PA66) are widely used in many different markets and applications due to their excellent performance/ cost ratios. Their key properties are listed below.

  • High strength and stiffness at high temperature
  • Good impact strength, even at low temperature
  • Very good flow for easy processing
  • Good abrasion and wear resistance
  • Excellent fuel and oil resistance
  • Good fatigue resistance
  • PA 6 has excellent surface appearance and better processability than PA66 (due to its very low viscosity)
  • Good electrical insulating properties
  • High water absorption and water equilibrium content limits the usage
  • Low dimensional stability
  • Attacked by strong mineral acids and absorbs polar solvents
  • Proper drying before processing is needed

Although, they exhibit similar properties, slight differences do remain. PA6 has a slightly lower temperature resistance versus PA66 and is also slightly less expansive.

Polyamide 6 vs. Polyamide 66 

While, as compared to PA6, the PA66 has:

  • Slightly less moisture absorption ability
  • Higher modulus
  • Better wear resistance
  • Better short term heat resistance


Injection Molding and Extrusion Processing Conditions


While processing PA6 and PA66 drying before is highly recommended. The moisture content should be a maximum of 0.2%. The maximum permissible drying temperatures lie in the range of about 80 to 110°C. Polyamide 6 and Polyamide 66 is thermally stable up to 310°C. At temperatures above this lead to decomposition, the initial products formed being mainly carbon monoxide and ammonia, and caprolactam. While processing PA6/ Polyamide 6 with an injection molding and extrusion techniques, the following conditions are recommended.

Injection Molding

  • L/D ratio of 18:22
  • The melt temperature should be between 240-270°C (PA6) & 270-300°C (PA 66)
  • The mold temperature should be in the range of 55-80°C

Extrusion

  • Only highly viscous grades can be processed by extrusion
  • A three-sections screw with a L/D ratio of 20-30 is recommended
  • The processing temperature during extrusion should lie between 240 and 270°C (PA6) & 270 to 290°C (PA 66)


Polyamide 11 (PA11)

Polyamide 11 (PA11)

Polyamide 11 (PA11) or Nylon 11 is a rare bio-based engineering plastic that is derived from renewable resources (castor plants) and produced by polymerization of 11-amino undecanoic acid.

Rilsan® is one of the first biosourced polyamide. Melting point of Polyamide 11 is 190°C.

Bio-based polyamide derived from renewable resources (castor plants)
Bio-based polyamide derived from renewable resources (castor plants)

Several properties of PA11 are similar to Polyamide 12 (PA12) but comparatively offers superior thermal and UV resistance, low water absorption and lower environmental impact. It displays good impact strength and dimensional stability.

Strengths Limitations
  • The lowest water absorption of all commercially available polyamides
  • Outstanding impact strength, even at temperatures well below the freezing point
  • Resistant to chemicals, particularly against greases, fuels, common solvents and salt solutions
  • Outstanding resistance to stress cracking, aging and abrasions
  • Low coefficient of friction
  • Noise and vibration damping properties
  • Fatigue resistant under high frequency cyclical loading condition
  • Ability to accept high loading of fillers
  • Highly resistant to ionization radiation
  • High cost relative to other polyamides
  • Lower stiffness and heat resistance than other polyamides
  • Poor resistance to boiling water and UV
  • Proper drying before processing is needed
  • Attacked by strong mineral acids and acetic acid, and are dissolved by phenols
  • Electrical properties highly depend on moisture content


Polyamide 12 (PA12)

Polyamide 12 (PA12)

Polyamide 12 (PA12) or Nylon 12 is a semi-crystalline thermoplastic which shows performance similar to Polyamide 11. It can be derived from both petroleum and renewable sources. It is an expensive polymer as compared to other polyamides.

Polyamide12
Molecular Structure of Polyamide 12

Key Properties of PA12


  • It possesses lower impact resistance but shows good resistance to abrasions and UV
  • It has a low water absorbency than PA 6, PA66 and all other types of polyamides
  • The PA12 grade displays good dimensional stability and reasonable electrical properties
  • PA12 is ideal for applications where safety, durability or reliability over time is critical.
  • PA12's transparent grades are also available, allowing high flexibility in terms of design and creation

Strengths Limitations
  • Lowest water absorption of all commercially available polyamides
  • Outstanding impact strength, even at very low temperatures
  • Good chemical resistance, in particularly against greases, fuels, common solvents and salt solutions
  • Outstanding resistance to stress cracking
  • Excellent abrasion resistance
  • Low coefficient of friction
  • Noise and vibration damping properties
  • Good fatigue resistance under high frequency cyclical loading condition
  • Expensive than other polyamides
  • Lower stiffness and heat resistance than other polyamides
  • Low UV resistance
  • Proper drying before processing is needed
  • Electrical properties highly depend on moisture content

In contrast to traditional bio-based polymers, PA11 and bio-sourced PA12 demonstrate the features shown in the image below.

PA11 PA12 Features


  • Even if they do not over-perform in terms of temperature resistance (HDT, peak temperature...), they exhibit outstanding retention of performance over time
  • Their remarkable long lasting performance allows for their use in a wide range of conditions (temperature, pressure, chemical...)
  • PA11 and PA12 are particularly suitable when reliability over time is needed


PA 11 & PA 12 Processing Conditions


Drying before processing is highly recommended : 6-12 h at 80-90°C. Target moisture content should be a maximum of 0.1%.

Injection Molding

  • For the plasticating unit, a three zone screw with a L/D ratio between 18 and 22 is recommended
  • Melt temperature: 180 - 230°C 
  • Mold temperature: 30 - 100°C
  • Decrease of mold temperature very often eases de-molding but a decrease of crystallinity then occurs

Extrusion

  • General temperature setting depends very much on resins to be processed and type of extrudate, thus a general recommendation can not be given
  • Temperature in first heating zone: ~ 200°C
  • Conventional three zone screw with a L/D ratio of at least 24 is recommended
  • Mixing and shear elements may be useful to increase the melt homogeneity
  • Cooling of the feeding section is mostly required


Polyamide 6-10 (PA 6-10)

Polyamide 6-10 (PA 6-10)

Polyamide 6-10 (PA 6-10) is a semi-crystalline polyamide. PA 6-10 is produced by the polymerization of hexamethylene diamine with a dibasic acid i.e sebacic acid this this case. Melting point of polyamide 6-10 is 223°C. Main properties of Polyamide 6-10 are listed below.

  • Exhibits lower water absorption when compared to PA6 or PA66
  • Has lower brittle temperature than PA6 or PA 66
  • Has good abrasion resistance and chemical resistance
  • Possesses lower strength and stiffness unlike PA 66
  • Drying before processing of PA 6-10 is highly recommended
  • PA 6-10 is much stronger than PA 11, PA 12 or PA 6-12
  • Low coefficient of friction
  • Good electrical insulating properties
  • High resistance against high energy radiation (gamma and X-rays)

Few limitations of PA 6-10 include: high mold shrinkage, high cost compared to other low water absorption polyamides and it is attacked by strong mineral acids and absorbs polar solvents.

Thanks to its good insulating properties, heat resistance and flame retardancy, Polyamide 6-10 is used to manufacture insulators for the electrical market.


Polyamide 46 (PA46)

Polyamide 46 (PA46)

Polyamide 46 (PA46) or Nylon 46 is manufactured by polycondensation of adipic acid and 1,4-diaminobutane. Diaminobutane is synthesized from acrylonitrile and HCN. Melting point of polyamide 46 is 295°C.

Polyamide 46 (PA46) is a high temperature polyamide providing unmatched performances across a broad range of applications.

  • Automotive - It is used to manufacture several automotive/ transportation parts like chain tensioners, engine covers, oil filter parts, signaling lamp bases, thrust washers, gear-shift forks, speedometer gear wheels, fuel distributors, etc.
  • E&E, - It is used to manufacture surface-mount devices, connectors, end laminates in electric motors, brush holders in electric motors, etc. for the electronics market
  • Industrial goods, , consumer goods, safety controls in appliances such as kettles and ovens
  • And many more

PA46 is the polyamide exhibiting the highest temperature resistance. Its HDT at 1.8MPA is 160°C, and 285°C when filled with 30% of glass fibers. PA 46's mechanical resistance is superior to PA66's. Its fatigue resistance is 50 times that of PA66.

Key Properties of PA46


Excellent thermal performance with Polyamide46
PA46 mechanical properties
Excellent wear resistance with PA46
Chemical resistance with PA46
Excellent electrical resistance with PA46
Good Thermal
Performances
Good Mechanical
Properties

Particularly at high
temperatures
Excellent Wear
Resistance
Excellent Chemical
Resistance
Excellent Electrical
Resistance

  • PA46 is often used to replace metal in demanding, high temperature applications.
  • Due to PA46's excellent mar and wear resistance, it is used in gear applications where it offers a combination of mechanical and constant performances at high temperature, excellent tribological behavior and high fatigue resistance.
  • PA46 can be metallized. It is also possible to color a part made of PA46, however the color resistance will depend on the behavior of the pigments at high temperature.
  • Due to its high fluidity, PA46 is a good solution for complex shapes and parts with thin walls.

Strengths Limitations
  • Outstanding stiffness, fatigue and creep resistance, up to 220°C
  • Excellent abrasion and friction behavior
  • Very good flow for easy processing
  • Very low injection cycle time, due to its high crystallization rate
  • Excellent fuel and oil resistance
  • Good impact strength
  • Very low flash
  • Good electrical insulating properties
  • High resistance against high energy radiation (gamma and X-rays)
  • High water absorption and water equilibrium content
  • High temperature processing, due to its high melting point
  • Low dimensional stability
  • Attacked by strong mineral acids and absorbs polar solvents
  • Proper drying before processing is needed
  • Darkens with exposure to high heat

Polyamide 46 Processing Conditions


Polyamides are hygroscopic in nature and hence tend to absorb moisture when left in open. It is therefore highly recommended to dry Polyamide 46 for 2-8 h at 80°C before processing. This ensures that hydrolytic degradation does not occur. Target moisture content should be a maximum of 0.1%. For critical applications, the recommended moisture content is 0.05% or less. In this case, it is recommended to pre-dry pellets 24-100 h at 80-105°C.

  • Polyamide 46/PA46/Nylon 46 can be processed on standard reciprocating screw injection molding machines.
  • An L/D ratio of at least 20 is recommended.
  • Melt temperature should lie between 300-330°C
  • Mold temperature  should be in the range of 60-120°C.
  • Polyamide 46 does not stick to the mold surface and has good ejection properties.


Polyphthalamide (PPA)

Polyphthalamide (PPA)

Polyphthalamides are formed by reaction of aromatic acids with aliphatic diamines and produced using a combination of terephthalic acid and isophthalic acids.

Polyphthalamide also known as PPA is a high heat resistance semi-aromatic polyamide.

With its low moisture pick up, PPA demonstrates excellent retention of performances in a wide range of conditions, such as harsh chemical environment and extreme temperature conditions. They also demonstrate excellent stiffness and creep resistance.

Thanks to their aromatic structure, Polyphthalamides (PPA) offer several superior performances compared to other polyamides, Some of its properties are listed below.

  • Improved dimensional stability
  • Improved solvent and hydrolysis resistance
  • Better high temperature mechanical property retention

Polyphthalamide are stronger, less moisture sensitive and possess better thermal properties compared to the aliphatic polyamides such as PA66. However, they are less ductile in comparison although impact grades are available.

Polyphthalamide resin features an excellent stiffness-to-cost ratio and a high strength-to-weight ratio, both of which are superior relative to PBT, PPS, PEI, PET and PA 66. And, its thermal performance is exceeded only by polyetheretherketone (PEEK) and some Liquid Crystal Polymers.

Strengths Limitations
  • Very high stiffness and strength, compared to PA66
  • Good heat, chemical and fatigue resistance
  • Low water absorption
  • Very low creep tendency
  • Good dimensional stability
  • Requires high processing temperatures (up to 350°C)
  • Requires good drying equipment
  • Not inherently flame retardant
  • Attacked by powerful oxidants, mineral acids, acetic acid and formic acid


Polyphthalamide Injection Molding Processing Conditions

  • Drying is recommended : 2 h at 120°C or at least 8h at 80°C
  • Holding the melt at temperatures above 350°C may result in polymer degradation and should be avoided.
  • A melt temperature of 320-345°C is recommended.
  • A mold temperature of 80-140°C is recommended.
  • A screw with a L/D ratio of 18-22 should be used during plasticizing phase.


Nylon Versus Polyester: Main Differences

Nylon Versus Polyester: Main Differences

Both nylon and polyester are thermoplastic materials but polyester compounds can be thermosets as well. They both are majorly synthetic in nature. Their main differences are listed in the table below.

Nylon Polyester
Type Thermoplastic Polymers commonly known as Polyamides Thermoplastic or Thermoset
History First Nylon was produced by Wallace Carothers in 1935 First polyester fiber called Terylene created in 1941
Production Nylon is formed by the condensation of copolymers. Equal parts of dicarboxylic acid and diamine are used for the process. There are peptide bonds on the ends of the monomers Synthetic polyesters are made up of dimethyl ester dimethyl terephthalate (DMT) or the purified terephthalic acid (PTA).
Uses Used in apparel, flooring, molded parts for cars, electrical equipment, etc., packaging films Used to manufacture a variety of products, including textiles, belts, furniture, insulation, padding, tarps and glossy finishes for hardwoods
Touch A silky, smooth touch Fiber feeling
Durability Exceptionally strong, abrasion resistant, resistant to damage from oil and many chemicals Strong, resistant to stretching and shrinking, resistant to most chemicals, crisp and resilient wet or dry, abrasion resistant
Stretchability Low moisture absorbency allows fabric to stretch No water absorbance, faster drying, wrinkle resistant


How to Process Polyamide?

How to Process Polyamide?

Polyamides can be processed by all common melt processing techniques. Though low melt viscosity polyamides needs particular attention. Sure to their semi-crystalline nature processing must be controlled to optimize the physical properties of the end component.

Thanks to their crystalline structure Polyamides are easy to inject, showing high fluidity. This is particularly appreciated when injecting thin-walled parts.

Due to their moisture sensitivity, Polyamides require efficient drying process. Insufficient drying will lead to splays and unaesthetic marks on part surfaces, as well as lower mechanical properties due to material degradation (heat and water lead to oxidation).

Injection Molding


All polyamide materials can be processed by injection molding.
  • If the moisture content is >0.2%, drying in a hot air oven at 80°C (176°F) for 16 hours is recommended. If the material has been exposed to air for more than 8 hours, vacuum drying at 105°C (221°F) for more than 8 hours is recommended. 
  • Mold Temperature: 60-80°C
  • Melt Temperature: 230 - 280°C; 250 - 300°C for reinforced grades
  • Material Injection Pressure: 75 - 125 MPa (depends on material and product design)



Extrusion


  • Maximum allowable moisture content 0.1%
  • Melt Temperature: 230-290°C
  • The compression ratio: <4.0
  • The L/D Ratio: 25-30 (Barrier Screw or Polyolefin Screw with equal feed, transition and metering section)

3D Printing


Polyamides are also widely used to produce 3D parts printed by selective laser sintering (SLS). 3D printing technique used to produce plastic prototypes offer several benefits such as production of complex parts, individual designs, cost-effective in small scale production.



Watch Today! An Interesting Video on Tips and Tricks for Nylon 3D Printing

Polyamide Recycling and Toxicity

Polyamide Recycling and Toxicity

The key use of polyamide 6 is in carpets and a recycling process for this was initially devised by DuPont in 1944 although recycling a dirty carpet is still a challenge.

Polyamide polymer can be chemically recycled or de-polymerized

De-polymerization method involves breaking down the long polymer chains into monomers which can be then re-polymerized which possibly converts the waste into products having a quality equivalent to that of the “virgin” polymer.

Polyamide 6 can be depolymerized to its monomer – caprolactam, byacidolysis, hydrolysis, aminolysis or catalyzed-de-polymerization in vacuum. Companies recycling polyamide 6 and 6.6 by depolymerization includes: DuPont, AlliedSignal, BASF and Novalis Fibers.

Other recycling method include recovery of polymer components without reaching the monomer level. Includes multiples extraction and separation steps, Mechanical recycling and Thermal recycling or Energy generator.

Polyamide Recycling from Carpets
(Source: AlliedSignal/NCSU)


Key Applications

Key Properties

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