This study is to evaluate the effect of curing and casting methods on the physicochemical properties of polymeric coating systems. Aqueous-dispersion-based and organic-solvent-based Kollicoat® SR30D (poly(vinyl acetate)) and Kollicoat® MAE100P (poly(methacrylic acid-ethyl acrylate)) free films or film-coated pellets were used to evaluate the physicochemical properties resulting from different solvents and different curing treatments.
Diffusion coefficients of water in organic-solvent-based films were lower than those in aqueous-dispersion-based films. Increases in curing temperature and curing time decreased the diffusion coefficient. Regardless of preparation method, the tensile strengths of films increased with an increase in curing temperature and curing time. Changes in elongation percentage of the films were dependent on the polymer and curing. The tensile strengths of aqueous-dispersion-based SR30D films are lower compared to those of organic-solvent-based SR30D films. However, the “core-shell” structure is preserved in the aqueous-dispersion-based MAE100P film and formed a rigid frame, which greatly increased the mechanical properties of the films. Therefore, the tensile strength of aqueous-dispersion-based MAE100P films is greater than in the case of organic-solvent-based films. In swelling studies, water uptake and weight loss for all of the films increased with an increase in incubation time. The water uptake and weight loss of SR30D films cast from water were higher than those of organic-solvent-based films. However, contradictory results were observed for MAE100P films due to the core-shell structure in the aqueous-dispersion-based MAE100P films. An increase in curing time and temperature increased the Tg of SR30D films. Curing treatments led to a second glass transition temperature for MAE100P films, which may result from microphase separation.
Curing decreased acetaminophen release from pellets coated with an aqueous-dispersion-based SR30D film. Curing effects are also dependent on the coating formulation and coating parameters. The drug release rate from organic-solvent-based film-coated pellets was slower in comparison to pellets coated with aqueous-dispersion-based films. Acetaminophen release in 0.1 N HCl from aqueous-dispersion-based MAE100P coated pellets was reduced after the curing treatment. Curing has no effect on drug release for acetaminophen-containing pellets coated with organic-solvent-based SR30D or MAE100P films.
The ionization of surface carboxylic-acid groups on MAE100P polymer particles alters the properties of polymer films by increasing ionic aggregates and solubilizing the polymer chains. Increased ionic aggregates improve the mechanical properties of films. However, solubilizing polymer chains will change the film formation mechanism from a dispersion-based film to a solution-based film. Therefore, tensile strength was decreased with an increase in ionization degree. The drug release rates were continuously increased when the degree of ionization of surface acid groups increased.
Overall, curing and casting methods have significant effects on the physicochemical properties of SR30D and MAE100P films and on the drug release behavior from film-coated, drug-loaded pellets. The core-shell structure in aqueous-dispersion-based MAE100P films also greatly changed the properties of this film or coat.