Invented in 1935 by a DuPont chemist named Wallace Carothers, nylon is the generic designation for a family of polymers known as polyamides. They contain chains of monomers which are bonder together via amide bonds, hence the term polyamide. Nylon can be fabricated as a co-polymer, with two different types of monomer, or as a homoplymer using a single monomer. The type of nylon is designated by the number of carbon atoms in the base monomers. The most common types are nylon 6 and nylon 6/6, but there are also more specialized types including nylon 11, nylon 12, nylon 5/10, nylon 6/12, et al.
Nylon has some unique characteristics. First of all, it is a semi-crystalline material, and like most semi-crystalline materials has excellent chemical resistance. Second it has a relatively high melting point, so it is able to withstand high end-use temperatures. Third, it inherently has a great deal of lubricity, and excellent resistance to abrasion and wear.
Nylon also has good mechanical properties. It has good strength, and reasonable stiffness. It has good elongation, and a unique yield behavior under tension. Instead of undergoing brittle fracture, the material will continual to elongate and “neck down”, and the polymer chains will align in the direction of elongation, increasing its tensile strength. This phenomenon allows nylon to be drawn into fibers with very high strength. These fibers are used for fabric, carpet fibers, rope, and fishing lines.
Added together, polyamides offer an unparalleled combination of strength, stiffness, and elongation. One application that demonstrates this succinctly is a standard cable tie. The tail end of the tie provides the structure, and also has an angled gear rack molded-in. The head of the tie contains a flexible ratchet. This ratchet flexes to allow the tail to be inserted, and then flexes click-click-click over the gear rack as the tie is tightened. But if the tail is pulled backward, the ratchet locks in place, and the tail cannot be removed.
The chemistry also faciliates the use of specialty additives and modifiers. As a result, hundreds of different grades of nylon are available, including grades specially modified with lubricants, toughening agents, impact modifiers, processing aids, and structural reinforcement. Glass fibers are commonly used as for structural reinforcement. Glass reinforced nylon has become the material of choice for housings of high performance power tools due to its combination of strength, stiffness, durability, and chemical resistance.
Polyamides also have a unique chemical structure which allows for the use of dyes and colorants. Custom colors are easily achieved in the injection molding process through masterbatch concentrates, cube blending, or custom compounding.
Nylon is used in high performance applications in virtually every industry, including automotive, power tools, office furniture (chair bases and chair chells), and more. The grandfather of all plastics, nylon remains one of the world’s most widely used engineering materials.