A GUIDE TO NYLON

What is Nylon?

The term nylon refers to a family of plastics.  The two most common grades of nylon are Nylon 6 and Nylon 6/6.  The number refers to the number of methyl groups (See "A Guide to Polycarbonate in General" for an example of a methyl group) which occur on each side of the nitrogen atoms (amide groups).  The term polyamide, another name for nylon, reflects the presence of these amide groups on the polymer chain.  The difference in number of methyl groups influences the properties of the nylon.

Unlike polycarbonate, nylon is crystalline in nature; so the molecular chains do not have large substituent groups (such as the phenyl ring in polycarbonate).  The crystalline nature of the material is responsible for its wear resistance, chemical resistance, thermal resistance, and higher mold shrinkage.

What are the properties of nylon?

• very good physical properties
• moisture has significant effect on properties
• very good heat resistance
• excellent chemical resistance
• excellent wear resistance
• moderate to high price
• fair to easy processing

What is the difference between two different kinds of nylon?

As the separation of the amide groups increases (by adding more methyl groups) and the polarity of the amide groups is reduced, moisture absorbance is decreased.  Resistance to thermal deformation is lowered due to more flexibility and mobility in the methyl unit sections of the chain.  In the case of Nylon 6 and Nylon 6/6, the properties are not that different, but one can clearly see this relationship when comparing Nylon 6/6 to Nylon 6/12.  Nylon 6/12 has a lower modulus, higher elongation, lower strength, lower thermal distortion temperature, lower hardness, and lower melting point than Nylon 6/6.  However, Nylon 6/12 absorbs half as much water on Nylon 6/6.  Thus, even though the properties may not be as good as Nylon 6/6 in dry conditions; the properties of Nylon 6/12 will be much more consistent when it is used in applications in which water may be present.  The absorption of water has a significant effect on the properties of nylon.

What can be done about the absorption of moisture by water?

The absorption of moisture by nylon is a completely reversible reaction.  Drying before processing will drive off all but a small portion of water molecules.  The rate at which the nylon can be dried and at which it absorbs moisture varies with each grade of nylon.  Reinforcement of nylon helps to reduce these effects.  Heating to molding temperatures while wet will result in hydrolytic degradation, a reaction in which the molecular bonds are severed.

What are some common applications of nylon?

• electrical connectors
• gear, slide, cams, and bearings
• cable ties and film packaging
• fluid reservoirs
• fishing line, brush bristles
• automotive oil pans
• fabric, carpeting, sportswear
• sports and recreational equipment