A general model for predicting the baking behavior of a polymer film from poly(vinyl acetate)/methanol

摘要

Baking is very important for controlling the structure and properties of polymer thin films. The diffusion and mass transfer coefficients are two basic parameters for studying the baking mechanism. In this study, a general theoretical analysis of baking was developed to study the influence of various baking parameters on polymer film formation. In the literature, the mass transfer coefficient has generally been obtained from experimentally fitted data. In this study, a new model equation based on the boundary layer theory was developed to predict the mass transfer coefficient. The Vrentas-Duda equation was used to predict the variation of the diffusion coefficient with the concentration and baking temperature. The applicability of this model was justified by means of experimental data from poly(vinyl acetate)/methanol. The effects of the baking parameters on the film thickness and solvent residue were analyzed, including the mass transfer coefficient, diffusion coefficient, drying air velocity, baking temperature, and baking time. It was found that the baking mechanism could be shifted from the evaporation control to the diffusion control by increasing the baking time. The solvent distribution inside the film could be the same at different drying air velocities by applying different baking times. The baking temperature played a more significant role in the solvent residue content than the drying air velocity because it affected both the mass transfer coefficient and diffusion coefficient. The skinning phenomena could be largely reduced by increasing the baking temperature. [References: 27]