Polyamides (nylons) are a family of linear chain polymers.
The lower code number members (polyamide 6 and polyamide 6.6) have a higher concentration of amide link groups than the high code number members (polyamide 11 and polyamide 12).
Polyamides with a higher concentration of amide links are more polar than the high code number polyamides, which tend towards the properties of polyethylene.
Higher concentrations of amide links encourage cross-linking through hydrogen bonding. The lower the code number the higher the degree of crystallinity. The simple chain structure has reasonable flexibility and the glass transition temperature (Tg) will be 50°C and lower for the high code numbers
Identification
Polyamide is not highly flammable and typically exhibits a slow burn with a blue or yellow flame.
When extinguished, it may emit a distinctive odor, which can vary depending on the specific type and additives used.
Useful data
Density – 1.14 g/cm ³
Pre-Drying – 4 hours at 80°C in a dehumidifying hot air drier, unless taken directly from a hermetically sealed bag. PA is hygroscopic and so will absorb moisture if left in unsealed bags or containers.
Melt temperature – PA 6: 240-250 °C / PA 66: 270-290 °C
Mould Temperature – PA 6: 60-100 °C / PA 66: 60-100 °C
Shrinkage – PA 6: 0.7-2.0 %, if glass filled then 0.3-0.8 % / PA66: 0.7-2.0 %, if glass filled then 0.4-0.7 %
History
Wallace Carothers of DuPont discovered polyamide 6.6 in 1931. In October 1938 commercial production of nylon 6,6 began. The first commercial application were for the bristles for the Miracle Tuft toothbrush. The following year, nylon stockings became available and were a sensation at the World’s Fair in New York City
Nylon 6 was developed in the 1940’s (largely as a consequence of the patent that existed on Nylon 6,6). With the start of World War II, nylon was then commandeered for war purposes for example, to make canopies for parachutes. Nylon for injection moulding did not begin until the 1950’s.
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