The melt-phase kinetics and equilibrium of nylon polycondensation and the mass transfer of water under conditions of high temperature and low water concentration were investigated by experimental study and mathematical modeling. Nylon 612 was used as a more thermally stable alternative to nylon 66 in a novel reactor system. The water concentration in the melt was varied by altering the composition of a steam/nitrogen mixture bubbled through the stirred molten polymer. Experimental data for the time evolution of carboxylic acid and amine end-group concentrations, water concentration, and inherent viscosity of the polymer samples were collected and compared with the predictions of two mathematical models from the literature. A simplified mathematical model describes the experimental data as well as or better than the literature models and accounts for the solubility of water in the nylon melt, the mass transfer of water, the rate of reaction, and the variation of the apparent equilibrium constant with the water concentration.

An experimental investigation of nonoxidative thermal degradation kinetics of nylon 66 melt under high temperature (280–300 °C) and low water content (0.02–0.14 wt.‐%) conditions is presented. Experimental data for the time evolution of polymer end‐group concentrations and degradation‐product generation rates were compared with the predictions of the only published kinetic model. The omitted influence of water content is a plausible partial explanation for the considerable discrepancy between model predictions and some data. Several previously unreported or unquantified degradation products were identified and measured. Potential additional reactions to account for these results in future kinetic models are proposed.magnified image

The behavior of circular cylinders moving singly through water under the influence of gravity was studied with a motion picture camera over a range of particle. Reynolds number extending from 70 to 2400. The terminal velocity was determined for each particle and its drag coefficient was evaluated. At Re‐greater than 300, and in some cases as low as 80, the particle acquired a secondary motion, consisting of an angular oscillation about its mean orientation and a periodic lateral deviation from its mean path of fall. A resultant dependence of the drag coefficient on particle density was found to occur. A theoretical method of predicting the period of particle oscillation was developed from consideration of variations in the location of the front‐surface centre of pressure.

The effects of end-group balance and moisture level on melt-phase polycondensation reactions were investigated using nylon 612. The polycondensation reaction was determined to be firstorder in amine ends and first-order in carboxyl ends at the relatively high temperature (284°C) and low water concentration conditions (0-0.002 mass fraction) studied, which are encountered in the later stages of nylon polymerization processes. Using data from this study and the nonisothermal data of Schaffer et al. (Chemical Pathways and Kinetics of the Later Stages of Nylon Polymerization Processes. Ph.D. Thesis, Queen's University, Kingston, Ontario, Canada, 2003; Experimental Study and Modeling of Nylon Polycondensation in the Melt Phase. Ind. Eng. Chem. Res. 2003, 42, 2946), a mathematical model was developed that can accurately describe changes in both the polyamidation reaction rate and the apparent equilibrium constant, with changing water concentration and temperature.

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