Drying kinetics of polymer films



Drying kinetics of a polymer film cast from a polymer–soluent solution is studied. A modelization of the whole drying process is performed, including the difision of soluent through the varnish layer, the moving interface, and the coupled heat and mass transfer between the interface and the drying air. The assumptions and the ualdity domain of the proposed modelization are thoroughly analyzed. In particular, comparison of the varnish temperature with its glass transition temperature all along the process allows us to determine the validity domain of the Fickian difision assumption. Because of the hypodifisiue behavior of polymer solutions, uery large concentration gradients appear in the layer, and the drying kinetics is characterized by two successive regimes. This two- stage kinetics is investigated first for typical conditions encountered in the packaging industry, where a film of a few microns is dried in a few seconds, thanks to hot air blown through nozzles. Then, different drying conditions corresponding to evaporation experiments at room temperature of thicker films of the same varnish are studied.