Analysis of the permeation and mechanical characteristics of some aqueous-based film coating systems

The moisture permeability and mechanical properties of some aqueous-based free films have been evaluated using sorption-desorption and stress-strain techniques, respectively. These properties for blends of two film-formers--hydroxypropyl methylcellulose and polyvinyl alcohol--have been compared with those of hydroxypropyl methylcellulose films plasticized with polyethylene glycols. The polyethylene glycols generally increased the moisture permeability of hydroxypropyl methylcellulose films while polyvinyl alcohol decreased it. Both polyvinyl alcohol and the polyethylene glycols lowered tensile strength at break and Young's modulus but the effects of the polyethylene glycols were more pronounced. These results are discussed in terms of structural interactions between film components. All film systems evaluated, except that containing hydroxypropyl methylcellulose alone, exhibited a degree of anisotropy, a phenomenon with potentially adverse consequences in tablet film coating.