Mechanistic Insights into Drying and Film Evolution of PVA-Bentonite Coatings: The Role of Solids Content and Coating Composition Optimization.

Poly(vinyl alcohol) (PVA)-bentonite composite coatings combine a hydrophilic polymer with a naturally abundant clay mineral, offering potential advantages for modifying the physicochemical and film-forming characteristics of polymer-clay coatings. However, the combined influence of PVA-bentonite composition and total solids content on drying behavior and film evolution remains insufficiently explored. This study investigates the particle size, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), surface morphology, rheology, thixotropy, zeta potential, drying behavior, solvent transport, and film evolution of PVA-bentonite coatings prepared at total solids contents of 5 and 10 wt.% with different PVA to bentonite ratios. The drying profiles exhibited an initial relatively rapid solvent-removal stage followed by a slower stage associated with progressively restricted solvent transport during film consolidation. A lower total solids content (5 wt.%) generally accelerated drying but was associated with greater microcracking, whereas a higher total solids content (10 wt.%) produced more consolidated and comparatively uniform films with reduced solvent mobility. The combined physicochemical, rheological, drying, and morphological results demonstrate that both PVA-bentonite composition and total solids content substantially influence the structural organization and drying behavior of the coatings. Pure PVA formed a relatively uniform film but exhibited prolonged drying, while pure bentonite required the longest drying time (1083 min). Among the investigated formulations, the 50:50 PVA-bentonite coating demonstrated the shortest drying time, reaching equilibrium in approximately 480 min, while also exhibiting comparatively good film uniformity. During drying, its thickness decreased from approximately 1745 to 440 µm, corresponding to a reduction of about 1305 µm. Overall, under the investigated laboratory conditions, the 50:50 PVA-bentonite formulation provided the most favorable balance of drying behavior, film formation, and rheological characteristics among the compositions studied. These findings provide composition-structure-drying relationships that can guide further development of PVA-bentonite coating systems. At the same time, additional evaluation of mechanical, adhesion, barrier, durability, and economic performance is required to establish broader practical applicability.