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Drying and film formation of industrial waterborne latices



Experimental evidence is given for the mechanism of film formation from industrial waterborne latices using Inverse-Micro-Raman-Spectroscopy (IMRS). In the vertical direction of the film drying is gas-side controlled, indicated by uniform water concentration profiles. In the horizontal direction inhomogeneous drying resulting from a horizontal mass flux toward the edge of the film and the formation of a drying front are observed. The completeness of film formation is tested by so-called IMRS redispersion experiments. For hard latices (Texperiment ≃ Tmff) particle deformation is incomplete and the final coating—although transparent and optically clear—is a porous structure with a network of surfactant material located at the particle interfaces. The use of a film-forming aid lowers the polymer's minimum film formation temperature (Tmff) and facilitates particle deformation and polymer interdiffusion. The result is a nonporous film structure where individual particles and a network of surfactant material are no longer observed. IMRS redispersion experiments are compared with pictures of the final coating surface obtained from atomic force microscopy (AFM). © 2007 American Institute of Chemical Engineers AIChE J, 2007

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