COMPOSITION OF WATER-SOLUBLE SUBSTANCES IN POLYAMIDE-6 PRODUCED ON A CASCADE POLYAMIDE PRODUCTION LINE

摘要

Long-term observations of the composition of unextracted granulate and extraction water generated during the industrial process for producing PA-6 on a Polymer Engineering cascade polyamide production line have shown that despite fluctuations in the process parameters for synthesis of PA-6, on this line the amount of cyclic oligomers exceeds the equilibrium value by a factor of 1.6-1.7 and remains practically constant. The amount of residual caprolactam, on the other hand, depends considerably on fluctuation in these parameters, in a number of cases turning out to be less than the equilibrium values as a result of entrainment of its vapor from the polycondensation reactors by the stream of inert gas. From the data obtained, it follows that during the cyclic oligomer extraction process under commercial conditions, cyclic oligomers with n e" 5 are not completely removed. Concentrations of cyclic oligomers in the polymer granulate that are systematically higher than the equilibrium values should be considered as evidence that they are formed in excess in the "oligomer splitting" stage, preceding the actual hydrolytic polymerization of caprolactam, and that they slowly disappear during the latter stage.