Nylon, which belongs to the polyamide family, is one of the most versatile and widely used engineering thermoplastics in the industrial sector. In particular, the variants polyamide 6 (PA6) and polyamide 66 (PA66) are extensively used in injection moulding of plastic components due to their excellent combination of mechanical strength, low weight, dimensional stability, and good processability.
Although their names are similar, PA6 and PA66 present significant structural and performance differences, which influence the choice of material depending on the specific application.
In this article, we will analyse in detail their chemical composition, mechanical, thermal, and chemical properties, moisture behaviour, the use of reinforcements such as glass fibre, the optimal injection moulding parameters, and the main fields of application — with a particular focus on our manufacturing processes, developed through the experience gained by Corti Srl in technical moulding.
Nylon PA6 and PA66: structural differences and performance in industrial moulding
From a chemical standpoint, nylon PA6 is obtained through the ring-opening polymerisation of caprolactam, a cyclic monomer. Nylon PA66, on the other hand, is produced through the polycondensation of two different monomers: hexamethylenediamine and adipic acid. This difference in synthesis gives PA66 a more regular and crystalline molecular structure, characterised by more compact and linear hydrogen bonds.
The higher crystallinity of PA66 results in:
- a higher melting point: 255–260 °C (compared to 217–223 °C for PA6),
- lower shrinkage during cooling,
- and increased stiffness and wear resistance.
For these reasons, PA66 is often the preferred choice in applications where the component must withstand high temperatures and mechanical stress while maintaining dimensional stability.
PA6, on the other hand, thanks to its slightly less ordered structure, offers greater toughness and ductility. It can absorb impacts without breaking and is easier to process, as it requires lower processing temperatures.
In addition, PA6 tends to show higher moisture absorption compared to PA66, which may limit its dimensional stability, but in some cases can improve the resilience of the material.
| Property | Nylon PA6 | Nylon PA66 |
|---|---|---|
| Molecular structure | Less crystalline, less ordered structure |
More crystalline, more regular and compact structure |
| Melting point | 217–223 °C | 255–260 °C |
| Stiffness | Lower | Higher |
| Wear resistance | Lower | Higher |
| Toughness and ductility | Higher | Lower |
| Moisture absorption | Higher | Lower |
Mechanical, thermal and chemical properties, and moisture behaviour
Mechanical properties
Both materials offer excellent mechanical performance, but nylon PA66 stands out for having a slightly higher elastic modulus and tensile strength. This means that, given the same dimensions and geometry, a component made of PA66 will be stiffer and less prone to deformation under static loads or long-term stress.
Nylon PA6, while having comparable tensile strength, excels in impact resistance, making it more suitable for components subjected to vibrations, shocks, or dynamic stresses.
For example, in the case of a gear designed to withstand sudden impacts without chipping, PA6 may provide better durability than PA66, unless the latter is modified with elastomeric additives.
Additionally, PA6 offers good self-lubricating properties, which makes it ideal for moving components without the need for external lubricants. This combination of features makes it a particularly suitable choice for dynamic applications exposed to wear.
| Property | Nylon PA6 | Nylon PA66 |
|---|---|---|
| Elastic modulus | Slightly lower | Slightly higher |
| Breaking load | Slightly lower | Slightly higher |
| Tensile strength | Comparable to PA66 | Comparable to PA6 |
| Impact resistance | Higher | Lower |
| Self-lubrication | Higher (often does not require external lubrication) |
Lower |
Our tradition in nylon processing
As early as the 1970s, Corti Srl was manufacturing nylon components from the Akulon® family using injection moulding technology. These included gears and bushings for manual mechanisms used in industrial applications such as gate lifting systems and sunshade mechanisms.
Akulon® is a registered trademark of Envalior, with historical roots in Enka Glanzstoff Plastics N.V., a world-leading company in the production of high-performance technical polyamides.
These components are produced with complex geometries and require no additional machining, thanks to the high precision achievable through injection moulding.
Thermal properties
Nylon PA66 can operate continuously at temperatures of 120–130 °C, while nylon PA6 is recommended for use up to approximately 100 °C. Above these thresholds, PA6 loses stiffness more rapidly, limiting its use in high-temperature environments.
The service temperatures listed refer to the materials in their standard grades. The addition of additives or reinforcements, such as glass fibre or thermal stabilisers, can increase — or in some cases slightly reduce — the recommended operating range.
Furthermore, PA6 offers slightly better processability at lower temperatures compared to PA66. This represents a significant advantage, especially in the presence of complex moulds or when aiming to reduce production cycle times.
| Property | Nylon PA6 | Nylon PA66 |
|---|---|---|
| Continuous service temperature | ~ 100 °C | 120–130 °C |
| Processing temperature | Lower | Higher |
Chemical resistance
Both PA6 and PA66 offer excellent chemical resistance to oils, greases, fuels, and many organic solvents, but they are vulnerable to strong acids and particularly aggressive oxidising agents. In addition, some concentrated alkalis can degrade the molecular structure of polyamides, especially at elevated temperatures.
In general, chemical resistance depends heavily on the concentration and temperature of the chemical agents: a diluted solution may have no harmful effect, whereas the same compound in concentrated form and at high temperatures can significantly accelerate material degradation.
Moisture behaviour
Both materials are hygroscopic, meaning they absorb moisture from the surrounding environment. However, nylon PA6 absorbs a greater amount of water compared to nylon PA66: approximately 1.3% vs. 0.8%, under standard conditions of 23 °C and 50% relative humidity.
This higher moisture absorption may lead to more pronounced dimensional changes and loss of stiffness over time — a critical factor for applications requiring high dimensional precision and mechanical stability.
However, once saturated with moisture, PA6 can become tougher and less brittle, which can be beneficial in dynamic applications where resilience is more important than dimensional accuracy.
These characteristics make both materials suitable for a wide range of industrial environments, including conditions with high humidity or exposure to low-aggressiveness chemicals, such as marine applications, where corrosion resistance and moisture tolerance are essential.
| Property | Nylon PA6 | Nylon PA66 |
|---|---|---|
| Moisture absorption | ~1.3% (at 23 °C, 50% RH) | ~0.8% (at 23 °C, 50% RH) |
| Effect of moisture | Increased toughness and reduced brittleness in saturation conditions |
Minor impact on mechanical properties |
Glass fibre reinforced Nylon PA6 and PA66: advantages and limitations
Glass fibre reinforcement is one of the most common solutions used to improve the performance of polyamides. The addition of short fibres dispersed in the polymer matrix increases stiffness, elastic modulus, and dimensional stability, while also helping reduce both mould shrinkage and moisture absorption. Furthermore, it raises the continuous service temperature and improves wear resistance.
A typical example is PA66 GF30, which contains 30% glass fibre: this material combines the rigidity and thermal stability of PA66 with significantly lower shrinkage, making it ideal for structural components such as pump impellers or mechanical supports subjected to constant loads.
Reinforced PA6 is also widely used, especially when maintaining impact resistance is a priority, while still improving stiffness and wear resistance.
However, the use of glass fibre increases mould abrasion and can negatively affect the surface finish of the final part, making it less smooth. Additionally, reinforced materials tend to be less tough than their unfilled versions.
Injection moulding of Nylon PA6 and PA66: process parameters and quality
Injection moulding is the main technique used to manufacture nylon components. To ensure optimal results, every phase of the production process must be carefully monitored.
Nylon must be properly dried before processing, as residual moisture can cause surface defects, internal voids, and polymer degradation through hydrolysis. Recommended drying times:
- PA6: 12–16 hours at 80–90 °C
- PA66: 4–8 hours at the same temperature
These values may vary depending on environmental conditions, material grade, and initial moisture content.
Processing temperatures range from 230–260 °C for PA6 and 260–290 °C for PA66. Moulds are typically kept at 80–90 °C to promote polymer crystallisation during cooling, improving the mechanical properties of the moulded part.
Injection pressure usually ranges between 80 and 120 MPa, ensuring complete filling even in complex geometries.
As previously mentioned, PA6 may allow slightly faster cycle times than PA66, due to its lower processing temperature. However, its higher shrinkage requires tight control of cooling and accurate mould design to prevent warping or deformation.
The processing parameters provided should be treated as general guidelines and adapted based on component geometry, wall thickness, and the type of mould used.
Common injection moulding defects include:
- Silver streaks: caused by residual moisture
- Shrinkage and warping: due to uneven cooling
- Flash: from excessive pressure or improperly closed moulds
Careful parameter optimisation and mould maintenance are essential to prevent these issues.
Applications of Nylon PA6 and PA66 in the industries served by Corti Srl
Thanks to their outstanding properties, nylon PA6 and PA66 offer reliable and versatile polymer solutions across numerous industrial sectors. They can be used in both unfilled and glass fibre reinforced forms, expanding their application range and allowing them to replace metal components in many technical parts — reducing weight, cost, and improving corrosion resistance.
Below are some of the main application areas for the PA6 and PA66 solutions we develop for our clients, tailored to the specific technical requirements of each sector.
Marine industry
We manufacture boat accessories, structural parts, and fasteners that offer excellent resistance to marine corrosion and harsh environments.
Mechanical industry
We produce gears, pulleys, cams, bearings, and guides, using glass fibre reinforced grades to deliver lightweight, durable components that can replace metals and reduce the need for lubrication.
Hydraulics
We use PA66 GF30 for pump impellers and fittings, taking advantage of its excellent pressure resistance, thermal stability, and chemical resistance.
Furniture industry
We manufacture swivel castors for office chairs, joints, supports, and adjustable feet, leveraging the strength and smoothness of nylon. We also produce structural elements for the frames of beds, armchairs, and sofas.
Textile industry
We produce thread guides, toothed wheels, and wear-resistant parts, ensuring durability and resistance to mechanical stress.
Nylon PA6 or PA66: how to choose for industrial injection moulding
The choice between nylon PA6 and PA66 depends on several factors related to the specific requirements of the application.
- If the component must operate at temperatures above 100 °C, PA66 is generally preferred due to its higher thermal stability.
- For applications exposed to dynamic mechanical stress such as shocks or vibrations, PA6 offers superior resilience.
- When dimensional precision in humid environments is required, PA66 is more stable due to lower moisture absorption.
- If cost reduction is the goal, PA6 is more economical — not only because of its lower raw material cost, but also due to its lower processing temperatures and slightly faster cycle times.
In addition to standard grades, there are specialised variants designed for specific needs. For example:
- PA66 modified with elastomers (e.g. super-tough grades) improves impact resistance.
- PA6/66 copolymers combine the strengths of both materials, achieving a balanced profile of stiffness, toughness, and moisture absorption.
Conclusion
Nylon PA6 and PA66 are fundamental materials in industrial injection moulding. A deep understanding of their properties enables manufacturers to maximise performance across a wide range of applications.
With over sixty years of experience, Corti Srl is the ideal partner to advise, design, and manufacture custom nylon components, delivering precision, quality, and reliability.
Contact us for more information.
