Journal of Applied Polymer Science, Vol.87, No.3, 477-486, 2003
Guidelines for dryer design based on results from non-Fickian model
In polymer solution coatings below the glass transition temperature of the pure polymer, the coating can go undergo a glass transition and develop stresses during drying. When stresses develop, a non-Fickian model accurately describes solvent mass transport in drying polymer coatings. The non-Fickian model includes the solvent transport due to both stress and concentration gradients. This article presents a non-Fickian model, which predicts a lower residual solvent than does the corresponding Fickian model. We showed in an earlier article that the non-Fickian model predicts trapping skinning (higher residual solvent under more intense operating conditions) at higher drying gas-flow rates. In this article, the non-Fickian model was used to investigate how the gas-flow rate, dry film thickness, and substrate thickness affect the residual solvent for a single-zone dryer. This work recommends guidelines for choosing gas-flow rates, gas temperatures, and substrate thickness to minimize the residual solvent. The model predictions show that, at any gas temperature, the residual solvent is minimum at an intermediate gas-flow rate. The trapping skinning effect is less evident in thicker coatings and substrates.