THE MECHANICAL AND MOISTURE PERMEABILITY PROPERTIES OF AQUEOUS-BASED HYDROXYPROPYL METHYLCELLULOSE COATING SYSTEMS PLASTICIZED WITH POLYETHYLENE-GLYCOL

The effects of polyethylene glycols (PEG 400, 1500 and 4000) used as p lasticizer on the moisture permeability and mechanical properties of a queous hydroxypropyl methylcellulose (HPMC) films were evaluated with free films. The free films were prepared by using a pneumatic spraying technique similar to that used in fluidized-bed coaters. There was a clear relationship between some physical film properties and the molec ular weights and concentrations of the PEGs used as plasticizer. Over the range of concentrations tested, the moisture permeability of the f ilms decreased slightly as compared to unplasticized control films wit h increasing molecular weight of the plasticizer. The mechanical stren gth of the films was shown to be more dependent on the concentration t han on the molecular weight of the PEGs, while the ductility of the fi lms was mainly dependent on the molecular weight of the PEG. The addit ion of PEG at a concentration of 10% resulted in relatively hard and s trong films with a moderate elongation (ductility), especially when lo wer molecular weight plasticizers (PEG 400 or 1500) were used. As rega rds permeability to moisture and mechanical properties, the addition o f PEG at a concentration in the range of 10-20% of the polymer weight seems to be beneficial for aqueous-based HPMC film coats.