Design of water-based polyvinyl alcohol coatings using a drying modifier to minimize the residual solvent and coating defects

Polyvinyl alcohol–water coatings are promising amidst flammability, biodegradability, and environmental concerns, but exhibit deficient drying. Although surfactants are widely used in solubility enhancing and leveling-off films, yet their role as a drying modifier has been scarcely studied. Further, these drying studies are limited due to the absence of residual solvent minimization investigations. This work experimentally investigates the impact of fluorosurfactant, CAPSTONE FS-63, on the drying behavior of PVA–water coatings at different initial conditions. A wide range of modifier loading (0, 0.50, 1.00, 2.50, 5.00, and 7.50% by weight) was studied to yield the optimum loading. The residual solvent dropped by 85% with the optimum loading of 2.50% (by weight) in the coating of initially 5% PVA and 500 μm thickness. SEM images conformed to these results as the dried coatings up to 2.50% (by weight) loading yielded smooth, dense, and defect-free morphology, whereas higher loading values showed otherwise. On doubling the initial solution thickness from 500 to 1000 μm, the same optimum loading of 2.50% (by weight) was exhibited. However, the minimum residual solvent increased significantly from 0.51 to 1.16%, drying rate slowed down, and drying time increased significantly. On doubling the initial polymer concentration from 5 to 10%, the optimum loading reduced from 2.50% (by weight) to 1.00% (by weight). The minimum residual solvent, respectively, increased significantly from 0.51 to 1.20%, which can be attributed to the water affinity of PVA and threefold increase in solution viscosity. The TGA/DTG studies showed overall improved thermal stability of the coatings at optimized modifier loadings. The DSC results showed a slight decrease in glass transition temperature of the coating at optimized modifier loading. Graphical abstract