Koagulationsbadet

Koagulationsbadet is a liquid bath used in polymer processing to coagulate, precipitate, or regenerate a dissolved polymer as it exits a dope or casting solution. It is a central element in wet-spinning, membrane formation, and certain film casting processes, where exposure to a nonsolvent or chemical environment causes the dissolved polymer to solidify or phase-separate.

The mechanism involves solvent exchange and phase separation. When the polymer solution is brought into contact with the bath, the solvent diffuses out while a nonsolvent diffuses into the dope. This exchange reduces the polymer’s solubility and induces coagulation or precipitation, forming fibers, beads, or porous films. In some cases, the bath also chemically regenerates the polymer (for example, cellulose-based systems) or initiates cross-linking.

Bath composition varies with the polymer and desired product. Common baths are water-based and may contain acids, salts, or organic co-solvents to tune coagulation rate and morphology. For instance, viscose rayon processing uses an acidic coagulation bath with sulfuric acid and salts to regenerate cellulose; synthetic polymer spinning often uses water or water–alcohol mixtures as the nonsolvent.

Process control factors include bath temperature, pH, ionic strength, bath residence time, flow, and the concentration of additives. These parameters influence coagulation rate, fiber or film structure, and final mechanical properties. After coagulation, products typically undergo washing, post-treatment, and drying. Proper management of the coagulation bath is essential for product quality and environmental and safety considerations, including effluent handling and solvent recovery.