Effect Of Coagulation Conditions Research Articles

Effect of coagulation conditions on fine structure of regenerated cellulosic films made from cellulose/N-methylmorpholine-N-oxide/H2O systems

The important properties of cellulosic fibers in the conditioned state are mainly influenced by fine structure. In particular, the development of new methods of spinning regenerated cellulosic fibers made from a cellulose/N-methylmorpholine-N-oxide (NMMO)/H2O system require a better understanding of their fine structures in order to explain their special physical properties. The regenerated cellulosic films were made from cellulose/NMMO/H2O according to the degree of polymerization and solution concentration (wt %) of cellulose and the concentration (wt %) of NMMO in the coagulation bath. The quantification of crystal content was carried out by the resolution of the wide angle X-ray diffraction intensity distribution on the assumption that all diffracted intensities take the form of a symmetrical Gaussian distribution centering at its Bragg angle. The X-ray diffraction patterns resolved into individual integral intensities showed that the polymorphic structure mixed with part cellulose III and II was obtained for only coagulated cellulose films. The degree of crystallinity and apparent crystalline size of regenerated cellulosic films depended on the degree of polymerization, the solution concentration of cellulose, and the concentration of NMMO. The diameter of the microfibril decreased with an increase in the concentration of NMMO. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2681–2690, 1999

Effect of coagulation conditions on structure and properties of membranes from aliphatic polyamides

Polyamide membranes were cast by phase inversion from a protic solvent into coagulation baths varying in composition. The coagulants were classified by a 'coagulation value', obtained in separate titration experiments. The morphology of the top layer (skin) and cross-section (sublayer) of each membrane was determined by scanning electron microscopy. It was found that the coagulation value could be used as a prediction of membrane structure, which could also be correlated to performance. By increasing ammonia in the coagulation bath the membranes produced changed from sponge-structured microfilters to finger-structured ultrafilters. The movement of the coagulation front during membrane formation was measured by a video-microscopic technique, where thin sandwiched layers of dope were exposed to a coagulant environment, and the kinetics were found to follow Fickian diffusion behaviour.

Effect of coagulation conditions on crystal modification of poly(p‐phenylene terephthalamide)

AbstractPoly(p‐phenylene terephthalamide)(PTTA) films were prepared from sulfuric acid solution with various coagulants. X‐ray diffraction and infrared absorption measurements revealed that the crystal structure of the film coagulated with water showed a new crystal modification II, which was different from the one previously reported by Northolt and Tadokoro et al. The latter structure is called here modification I. Modification II coagulated with water from a solution of lower polymer concentration irreversibly transformed to modification I upon annealing, whereas modification II prepared from highly concentrated solution was thermally stable and scarcely transformed to modification I upon annealing. A liquid crystal‐like swollen structure was found in the intermediate stage of the formation of modification II. In this swollen state, x‐ray diffraction revealed that water molecules are included in hydrogen‐bonded planes and the intermolecular spacing along the van der Waals force direction was unaffected by the existence of the water and remained constant throughout the process of regeneration. Both modifications I and II were found to be stable on treatment with boiling solvents. The transformation of the swollen structure to modification I took place in boiling methanol and acetone.