Polyamides are one of the major engineering and high performance plastics because of their good balance of properties. They exhibit high temperature and electrical resistances. Thanks to their crystalline structure they also show excellent chemical resistance. Polyamides have very good mechanical and barrier properties. In addition, these materials can easily be flame retarded.
Polyamides are widely used in markets such as Automotive & Transportation, Electrical and Electronics, Consumer Goods to name a few. When reinforced with glass fibers (short or long), their stiffness can compete with metals, this is why Polyamides are often considered in metal replacement projects.
Some well-known Polyamides:
Among this large polymer family, several types of polyamides are particularly suited for given applications. The best choice depends on the set of performances needed as well as the economical constraints. The two most widely used PA are by far the PA6.6, also known as Nylon and the PA6. They are often extruded to manufacture fibers (textile industry) or films (packaging), or injected.
The Polyamides with the highest performances are PPA and PA4.6, which are good candidates for metal replacement developments or very specific applications exposed to extreme conditions.
Biobased PA are also available. For instance, PA11 is based on castor-oil chemistry.
However all Polyamides tend to absorb moisture due to the amide chemical group. Moisture acts as a plasticizer on Polyamides thus reducing tensile modulus and increasing impact resistance. This is why a particular care should be taken when reviewing polyamides technical data sheets (data split into "dry" and "at 50% RH" categories). Moisture uptake also has a huge influence on dimensional variations; this must be taken into account when designing parts.
Thanks to their crystalline structure Polyamides are easy to inject, showing high fluidity. This is particularly appreciated when injecting thin-walled parts.
Due to their moisture sensitivity, Polyamides require efficient drying process. Insufficient drying will lead to splays and unaesthetic marks on part surfaces, as well as lower mechanical properties due to material degradation (heat and water lead to oxidation).