Nylon 6/6, derived from the polymerization of hexamethylenediamine and adipic acid, displays superior characteristics compared to Nylon 6 due to its highly aligned and densely packed molecular structure. With enhanced crystallinity, higher melting point, slower permeability, and increased resistance to deformation, it offers exceptional toughness and wear resistance. This makes Nylon 6/6 an ideal choice for various industrial applications, particularly in bearings and wear-resistant components. Its advantages include high thermal resistance, dimensional stability, and lower stain permeability, ensuring durability and extended product lifetimes. These properties contribute to its suitability for a wide range of practical applications, emphasizing its environmental benefits and sustainability.
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Figure 1. Nylon 6/6
Nylon 6/6, derived from the polymerization of hexamethylenediamine and adipic acid, exhibits distinct characteristics due to its molecular structure. As a semi-crystalline polymer, Nylon 6/6 showcases a higher degree of atomic alignment compared to Nylon 6, leading to increased crystallinity. The hydrogen bonding in Nylon 6 occurs in two different arrangements, with approximately 50% exhibiting longer and weaker tilted hydrogen bonds. In contrast, Nylon 6/6 features a single hydrogen bonding arrangement where bonds align directly in a row, forming a robust and densely packed polymer structure. The unique molecular arrangement of Nylon 6/6 imparts superior properties compared to Nylon 6. Under similar processing conditions, Nylon 6/6 demonstrates enhanced crystallinity, greater order in alignment, a higher melting point (40°C higher than Nylon 6), slower permeability, and increased resistance to deformation. These characteristics highlight Nylon 6/6's structural superiority, emphasizing its suitability for various industrial applications where strength, durability, and thermal stability are paramount. 1
Nylon 6/6, a solid polymer of the nylon series, has been commercially available since , developed by DuPont. Renowned for its exceptional toughness, low friction coefficient, and excellent wear resistance, Nylon 6/6 serves as an ideal substitute for various materials, ranging from metals to rubber. Its application reduces the need for lubrication, eliminating wear and corrosion issues. The combination of cost-effectiveness and improved wear resistance makes Nylon 6/6 an excellent choice for numerous bearings and wear-resistant components. Manufacturing precision parts with Nylon 6/6 is straightforward using standard metal processing equipment, achieving tolerances of up to +/- .002 through experience. It is available in various shapes and sizes, often ground to size for easier turning. Both extrusion and casting grades of Nylon can be paired with various fillers to meet specific application requirements. Some manufacturers offer different grades and filled versions under names like Tecamid® and Nylatron®, catering to specific applications. Solid lubricants such as mineral oil, graphite, PTFE, and MoS2 provide low friction, while reinforcements like carbon fiber, Kevlar®, and glass offer increased strength and dimensional stability. 2
Nylon 6/6 stands out in practical applications due to its unique properties that offer significant advantages: Firstly, its high melting point and thermal resistance set it apart from materials like polypropylene, ensuring that Nylon 6/6 can withstand frictional heat without melting. With a higher melting point than Nylon 6, it provides enhanced safety and durability, making it ideal for various applications, including furniture moving scenarios. Secondly, Nylon 6/6 excels in dimensional stability, maintaining aesthetics over time. Compared to materials such as polypropylene and polyester, both Nylon 6 and Nylon 6/6 exhibit superior recovery characteristics in carpets. The more ordered and evenly bonded structure of Nylon 6/6 enhances its performance, ensuring that carpets retain their original appearance and texture for extended periods. Additionally, Nylon 6/6's tight and ordered polymer structure results in lower stain permeability compared to Nylon 6, acting as a barrier against stain penetration. This property allows for easier cleaning and prevents stubborn stains from setting in quickly. Moreover, products like Antron® Nylon, derived from Nylon 6/6, feature a hollow-core fiber structure that boosts stain resistance. Carpets made with Antron® Nylon demonstrate exceptional durability, with research indicating a 60% higher stain resistance compared to Nylon 6 carpets. Both Nylon 6 and Nylon 6/6 are recyclable, and manufacturers choose recycling methods based on environmental impact assessments, contributing to sustainability. Overall, Nylon 6/6's long-lasting aesthetic appeal and durability lead to extended product lifetimes, reducing waste and offering superior environmental benefits. 1
1. Lotz B. Rippled Sheets: The Early Polyglycine Days and Recent Developments in Nylons. Chembiochem. ;23(5):e.
2. Nylon® 6/6 (Polyamide). Ensinger.
Nylon (PA) 6 & 66 are both synthetic polymers called polyamides, with the numbers describing the type and quantity of polymer chains in their chemical structure. Most nylons, including 6 & 66, are semi-crystalline and possess good strength and durability for demanding applications.
Nylon Properties
As polyamides, Nylon 6 & 66, whilst having their own separate and distinct benefits, do share many of the same core properties:
Differences
So whilst Nylon 6 & 66 are very similar materials, they do provide slightly different characteristics. The reason for the differences is largely due to their differences in chemical structure. Nylon 6 is made from one monomer which has 6 carbon atoms whilst Nylon 66 is made from 2 monomers with each one having 6 carbon atoms, hence the Nylon 66 name.
NYLON 6
NYLON 66
Less crystalline
More crystalline
Lower mold shrinkage
Exhibits greater mold shrinkage
Lower melting point
Higher melting point
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Lower heat deflection temperature
Higher heat deflection temperature
Higher water absorption rate
Lower water absorption rate
Poor chemical resistance to acids
Better chemical resistance to acids
Withstands high impact and stress and better stands up to hydrocarbons
Better stiffness, tensile modulus and flexural modulus
Lustrous surface finish, easy to colour
More difficult to colour
An important difference between Nylon 6 & 66 is mold shrinkage. Nylon 6&#;s lower mold shrinkage adds reliability to final part dimensions which is beneficial whilst Nylon 66&#;s greater mold shrinkage, as it is exposed to cool air and solidifies, means the material&#;s shape changes more after processing, which must be accounted for.
Other key differences between the two nylons are water absorption rates and heat deflection temperatures. As Nylon 6 absorbs more water than Nylon 66 and has lower heat deflection temperatures, it is not suited to applications that are exposed to water at high temperatures. Nylon 66 would be a better choice between the two.
Typical Material Applications
Which One Should I Choose?
The needs of an application have to be considered in terms of processing, aesthetic appearance, and mechanical properties first, in order to decide whether Nylon 6 or 66 is more suitable.
Nylon 6 should be used if a lightweight engineering plastic is required to withstand high impact and stress. It has better aesthetic appearance than Nylon 66 due to its lustrous finish and is easier to dye. It is an ideal choice for applications in the automotive, industrial and military industries. Common applications include: gears, firearm components and automotive engine compartments. It is not ideal, however, for applications that are exposed to water at high temperatures due to its higher water absorption and lower heat deflection rate than Nylon 66, which would be a better choice.
Nylon 66 should be used if a high performing engineering plastic is required that will be exposed to higher temperatures. Additionally, its stiffness and good tensile and flexural modulus make it an ideal material for applications that need repeated long-term performance. Typical applications include: friction bearings, radiator caps and tire ropes.
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