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
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