Chemical pathways and kinetics of the later stages of nylon polymerization processes

Industrial production of nylon 66 by melt-phase polycondensation is hampered by thermal degradation reactions that proceed when temperature and polymer molecular weight are high. These reactions result in changes in end-group concentrations, evolution of low-molecular-weight products, branching and gelation. Accurate descriptions of these phenomena are required to formulate mathematical models of production processes, which in turn are used to design improved operating strategies and process equipment.; Experimental and modeling studies were performed to develop knowledge of polycondensation and thermal degradation of molten nylon 66 (and specifically, of the effects of temperature and water content). A custom stirred batch reactor system was designed and constructed. The system permits control of the water content via a steam/nitrogen sparge gas bubbled through the melt, and allows multiple samples of polymer, off-gas and condensate to be collected within each experimental run. As part of the reactor commissioning, glucose syrup was used as a room-temperature model fluid in a mixing study to verify the uniformity of the vessel contents.; In the first molten polymer experiments, nylon 612 was used as a more thermally stable alternative to nylon 66, so that polycondensation could be studied in the absence of thermal degradation. The experimental data were compared with the predictions of literature models, and a new kinetic and equilibrium model was developed that accounts for mass transfer and vapour-liquid equilibrium of water. Since the water content is a difficult-to-measure variable of key importance, a semi-empirical correlation based on Flory-Huggins theory was developed to predict water solubility in nylon melts.; Experiments involving thermal degradation of nylon 66 yielded end-group concentration changes, evolution rates of gaseous degradation products, and rates of formation of degradation products in the polymer. An improved model was developed to account for important reactions not included in the only model available in the literature.