SIMILARITIES, DIFFERENCES & APPLICATIONS

Many customers ask about the differences between Nylon 6 and Nylon 6/6, and which resin may be best suited for an application. This document will provide some general similarities, differences, and applications for Nylon 6 and Nylon 6/6. While both Nylon 6 and Nylon 6/6 are made of the same elements, they are created from different monomers which leads to the differences in their physical properties.

Similarities

Nylon 6 and Nylon 6/6 are both semi-crystalline polymers and contain the same elements of carbon, hydrogen, oxygen, and nitrogen. The polyamide chains of both nylons are also held together with hydrogen bonds. Due to their similar structures, the polymers possess comparable mechanical qualities regarding tensile and impact strength, elasticity, density, and moisture absorption. As a result, they can be used in many of the same applications such as textiles, consumer goods and automotive parts.

Differences

While the chemical properties of Nylon 6 and 6/6 are similar, there are differences that may help make decisions on which resin to use. Nylon 6 is synthesized via ring–opening polymerization with caprolactam, whereas Nylon 6/6 is made through a polycondensation reaction between hexamethylenediamine and adipic acid. Since Nylon 6 is an open structure and its hydrogen bonds are further apart than Nylon 6/6, it results in a lower strength and temperature resistance with a melting temperature of around 220°C. Nylon 6’s density is also slightly lower than Nylon 6/6. However, Nylon 6 is better than Nylon 6/6 for toughness and surface appearance.

Nylon 6/6 has greater strength and higher temperature resistance, with a melting point near 260°C, due to a tighter crystal structure with less openings and closer hydrogen bond alignment. It has higher stiffness and lower moisture absorption than Nylon 6.

The chemical resistance of both Nylon 6 and Nylon 6/6 is similar with only strong acids being of major concern. Both Nylon 6 and Nylon 6/6 absorb moisture. This moisture absorption has a plasticizing effect on the products. The strength properties are reduced about 25%, while the impact performance is improved by about the same 25%. Nylon 6 has about 20% greater moisture absorption than Nylon 6/6. So Nylon 6 is on the higher end of the property change, while Nylon 6/6 is on the lower end of the property change.

See below for a comparison of properties for unfilled and 33% glass reinforced Nylon 6 and Nylon 6/6.

Applications

Nylon 6 possesses a more resin rich surface appearance than Nylon 6/6, which works well in products that require good surface aesthetics and do not require higher heat and wear resistance. This may include items such as automotive door handles and roof racks where the appearance of the part is critical. Nylon 6 is also well suited for applications such as office furniture and firearm parts because of its superior surface appearance and higher impact performance.

Nylon 6/6 is preferred for under-the-hood automotive parts such as cylinder head covers and cooling system components, where higher temperatures are of concern. Nylon 6/6 is often used in molding parts such as fasteners and cable ties; in this case, added strength is a benefit. Additionally, those applications are typically impact modified, and the Nylon 6/6 has a higher affinity. In cooling systems, Nylon 6/6 is preferred due to the lower moisture absorption and associated property change.

In the end, Nylon 6 and Nylon 6/6 can often be interchangeable in many applications. But when the application details are examined closely one of them will stand out as the better choice.