Diffusion of water and caprolactam in nylon 6 melts

Abstract

SynopsisThe diffusions of both caprolactam and water from nylon 6 melts have been measured using a semiinfinite geometry. The process involving diffusion and chemical reaction was analyzed utilizing Higbie's penetration model and known kinetic data. The caprolactam and water diffusion coefficients are, respectively, 8 X lo-* and 2.5X cm2/sec. Using the data, molecular weight profiles were obtained for both semiinfinite and cylindrical geometries as a function of melt depth and time.

Mathematical Modeling of Nylon 6/6,6 Copolymerization: Beneficial Influence of Comonomers on Degree of Polymerization in Batch Reactor

“…The lumped mass‐transfer coefficient of water ( k w A s = 50 h ‐1 shown in Table ) used in this study was obtained from the range of values shown in Table of the article by Schaffer et al, taking into account the type of stirring and the reactor size. To our knowledge, the only mass‐transfer coefficient value for caprolactam during nylon 6 polymerization is provided by Reimschussel . Unfortunately, Reimschussel's value was obtained for a closed batch reactor, which is expected to have much lower mass‐transfer rates than the current reactor system.…”

“…Mass transfer of volatile species during nylon 6 and nylon 6,6 polymerization has been considered in previous modeling studies. [37,38,40,46,48,[53][54][55][56][59][60][61][62][63][64][65][66][67][68][69][70][71] A literature review by Schaffer et al [71] found that typical values of the lumped mass-transfer coefficient k w A s , where A s is the surface area, range from a low value of 8 h -1 for a labscale reactor system with no nitrogen bubbling or stirring to a high value of 324 h -1 obtained in a two-phase twinscrew extruder reactor. Appropriate values of k w A s for use in mathematical models depend on the type and size of reactor and agitator, the agitation speed, reactor geometry and physical properties of the liquid phase.…”

“…To our knowledge, the only mass-transfer coefficient value for caprolactam during nylon 6 poly merization is provided by Reimschussel. [62] Unfortunately, Reimschussel's value was obtained for a closed batch reactor, which is expected to have much lower mass-transfer rates than the current reactor system. The typical value of mass-transfer coefficient for HMD during nylon 6,6 polymerization has also not been published in the literature.…”

A Kinetic Model for Non‐Oxidative Thermal Degradation of Nylon 66

“…We selected twice the half‐width because Variziri's confidence intervals were obtained using linearization and might be overly conservative. The upper and lower bounds for ( k L a ) w were obtained based on values from the literature 38, 39. Upper bounds for the remaining parameters and initial guesses were selected based on our judgment about physically reasonable values.…”

Simulation of three‐stage nylon 6 reactors with intermediate mass transfer at finite rates

“…Both r l and r2, in general, would depend on the physical properties of the reaction mass as well as the shape of the sparger, but these have been treated as parameters in this study. A similar model for the mass transfer of condensation product has been studied earlier for ARB polycondensations characterized by unequal reactivity of functional gro~ps.3~, 33 For nylon 6 polymerization, the mass balance equations are given in Table 11, where D, is the diffusivity of water, W , through the polymeric reaction mass and In writing these equations, the following assumptions have been made: 36 has this approximation been relaxed where the diffusion of monomer along with W has been considered. It was shown that the diffusion of the former is small because of its low concentration and diffusivity.…”