Nylon 66 Polyamide Resin

Polyamides (nylon) are the oldest and largest volume engineering polymers. Nylon was introduced in 1938 by DuPont as the world's first synthetic fiber, and by 1941 the company had introduced the first injection moldable grades. There are many types of thermoplastic polyamide resins commercially available. Commonly used products are designated as nylon 6; 6,6; 6,9; 6,12; 11; and 12, with the nomenclature designating the number of carbon atoms that separate the repeating amide group.

Two basic reactions are used to synthesize polyamide engineering resins: (1) polycondensation of a dibasic acid and a diamine or (2) polymerization of an amino acid or lactam. The most widely used nylon polymers are semicrystalline products with molecular weights of 10,000-40,000 and chemical structures in which amide linkages connect aliphatic chain segments.

Nylon Polyamide resins provide a mix of properties. Generally, the polyamide analogs exhibit good chemical resistance and low moisture absorption at the expense of heat resistance, impact properties in wet environments, and stiffness. All polyamides are hygroscopic to some extent. Water acts as a plasticizer in polyamides, reducing most mechanical and electrical properties while improving toughness and elongation. This problem, perhaps the major shortcoming of the nylons, is a function of the concentration of the amide groups. Water actually replaces the amide-amide hydrogen bonds with an amide-water hydrogen bond.

Nylon 66 Polyamide Resins provide very good mechanical and thermal properties in their dry-as-molded state, but are most susceptible to deterioration due to moisture absorption. Nylon 66 Polyamide Resins also provide many desirable properties to fulfill end-use requirements and account for the major share of the polyamide resins sold. Although property differences do exist between the materials, they are similar enough that the selection of nylon 6 or 66 for an application is largely a matter of customer preference for either product.

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