1978 Volume 35 Issue 12 Pages 771-778
After-polycondensation of polycaprolactam was investigated using a pilot plant consisted of a pressurized continuous reactor, an atmospheric equilibrium reactor, and a vacuum evaporator. The properties of the polymer obtained from the first reactor coincided with those estimated from equilibrium polymerization experiments in a closed system. After-polycondensation process in falling thin film and the evaporation of caprolactam in the evaporator were analyzed by treating the falling liquid as a hydrodynamic system. It was found in this analysis that the rate of polycondensation in the falling film system can be well explained using the rate constants deduced from static polymerization experiments. Meanwhile, at the bottom of the evaporator, the rate of polycondensation was lowered because of the difficulty in removing the water from the system. By adopting a modified equation for the bottom part, the polycondensation process in the evaporator could be completely explained. It was also deduced that there was a critical limiting depth of the reaction system to make the water evaporation from the polymer impossible. Analysis of the whole experimental data indicates that the reaction rate depends upon other factors such as contents of chain stabilizers and H3PO4, temperature, pressure of steam, and retention time.
