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Polycaproamide granules were obtained by anionic polymerization of caprolactam in ethylbenzene, using the sodium bis(2‐methoxyethoxy) aluminium hydride/isophorone diisocyanate catalytic system. Under these conditions, polymerization occurs heterogeneously and the nature of the particle growth seems to be essentially a microbulk one. The most suitable reaction conditions were established. The morphology of the granules was investigated by scanning electron microscopy. These granules result from the coalescence of a great number of small, spherical particles. the coalescence occurs during solidification of the separated polymer. Numerous globular formations were observed at the surface of the particles. The particles were individualized through mechanical dispersion and measured, and the average number of particles composing the aggregates was calculated. Using wide‐angle X‐ray scattering and differential scanning calormetry technics, the crystalline structure of the granular polycaproamide was studied. It contains almost entirely the α phase. The heat of fusion decreases slightly as compared with that corresponding to the anionic bulk polycaproamide. A schematic mechanism containing the stages involved in the obtaining of the granular polycaproamide is proposed. © 1996 John Wiley & Sons, Inc.

This article reports on the reaction of urease immobilization through its covalent bonding on carboxymethylcellulose. The reaction is activated by dicyclohexylcarbodiimide. The coupling reaction is influenced by the enzyme-support and activator-support ratios, as well as by duration. Starting from a rotating, composed experimental program of the second order, the function correlating the activity of the immobilized enzyme with the reaction parameters is established. Immobilized urease exhibits thermal stability higher than that of free enzyme, regarding both pH and the inhibiting action of some metal ions or organic substances. The stability over time of the immobilized urease is high, its enzymatic activity being maintained at over 85% of the initial value three months after synthesis.

Polyamide (PA) fine powders or granules, obtained by anionic solution/suspension polymerization of lactams, were used for the sorption of reactive dye Brilliant Red HE-3B from aqueous solutions. They provided a relatively large surface area and porosity that allowed an increased sorption rate. The visible molecular absorption spectroscopy was used to evaluate the performance of the investigated systems. Under the same conditions, the sorption capacity of polyamide particles decreases in the following manner: PA6-powders > PA12-powders > PA4-granules. The effect of pH, initial dye concentration, temperature, and sorption duration on dye removal was studied for the PA6-powder/reactive dye system. The equilibrium sorption isotherms have been analyzed by the linear, Freundlich, and Langmuir models. The data conform to a Langmuir isotherm and a pseudosecond order kinetic model, respectively. In addition, the apparent thermodynamic parameters were calculated and the obtained values support the conclusion that the reactive dye molecules are adsorbed onto PA-powders by an entropy-driven, endothermic process.

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SYNOPSISPolycaproamide granules were obtained by anionic polymerization of caprolactam in ethylbenzene, using the sodium bis( 2-methoxyethoxy)aluminium hydride/isophorone diisocyanate catalytic system. Under these conditions, polymerization occurs heterogeneously and the nature of the particle growth seems to be essentially a microbulk one. The most suitable reaction conditions were established. The morphology of the granules was investigated by scanning electron microscopy. These granules result from the coalescence of a great number of small, spherical particles. The coalescence occurs during solidification of the separated polymer. Numerous globular formations were observed at the surface of the particles. The particles were individualized through mechanical dispersion and measured, and the average number of particles composing the aggregates was calculated. Using wide-angle X-ray scattering and differential scanning calorimetry technics, the crystalline structure of the granular polycaproamide was studied. It contains almost entirely the a phase. The heat of fusion decreases slightly as compared with that corresponding to the anionic bulk polycaproamide.A schematic mechanism containing the stages involved in the obtaining of the granular polycaproamide is proposed.