Drying of polymer films with pre-loaded drying gas
By means of Inverse-Micro-Raman-Spectroscopy (IMRS) concentration profiles in transparent thin layers are monitored. Results provide us with detailed information about the drying process.
During the drying process of e.g. toluene-polyvinylacetate (PVAc) the formation of a thin skin at the surface is observed, because of the strong decrease of the diffusion coefficient with decreasing solvent content (see below). Pre-loading the drying gas can significantly reduce this diffusion controlled skinning. The solvent vapour content in the gas phase is adjusted by means of air flow controllers and a saturator.
In the diagrams below the influence of two different solvent vapour contents (aMethanol = 0.5 and aMethanol = 0.8) is shown.
When overflowing the toluene-PVAc film with the pre-loaded gas (after t = 10 min) is started, methanol diffuses in the film and the evaporation of toluene is forced. After stopping the pre-loading (t = 20 min), methanol evaporates very quickly. An overall reduction of the drying time can be achieved.