Making Polyamide 6
Caprolactam has typically been converted to PA 6 in a batch process,
heating it with water and ethanoic acid (to regulate the length
of polymer chain produced) for 12 hours at about 350°C.
Continuous production is always preferable, however, and this
is also possible. The reaction vessels used are designed to allow
more precise temperature control, with heat being removed and
recycled. This means the operating temperature does not exceed
280°C, but a higher percentage of caprolactam is polymerised
during the 16-20 hours spent in this stage of the process.
Unreacted caprolactam is extracted and re-fed into the reactor,
along with waste polymer from later processes. This constant recycling
helps keep waste to a minimum.