Interaction Phenomena in some Aqueous-Based Tablet Coating Polymer Systems.

Molecular interactions in aqueous-based tabletfilm coating systems consisting of hydroxypropyl methylcellulose (HPMC) in combination with either polyvinyl alcohol (PVA), polyethylene glycol (PEG) 400 or PEG 1000 have been investigated by viscometry and thermal analysis. The viscosity results indicate that the solvent (water) inhibited polymer-polymer interaction and this inhibitory effect was directly related to the solvent affinity of the polymer additive. The presence of crystallinity in the films was examined using a differential scanning calorimeter (DSC). HPMC/PVA blends were partially crystalline but the plasticized HPMC films showed no signs of crystallinity. Glass transition data were also obtained with the DSC. The plasticizer effects of PEG 400 and PEG 1000, respectively, in HPMC were confirmed by the fall in the glass transition temperature (Tg) of HPMC. On the other hand, incorporation of PVA increased the Tg of HPMC, and this was attributed to the presence of a crystalline phase in the blend. Maximum compatibility levels of PVA, PEG 400 and PEG 1000 in the polymer blends were found to be 40, 20 and 15 wt %, respectively, based on glass transition data.