Abstract
Abstract The glass transitions in talc- and titanium-dioxide-filled free films of hydroxypropyl methylcellulose (HPMC) as well as HPMC in combination with either polyethylene glycol (PEG) 400 or polyvinyl alcohol (PVA) have been examined by differential scanning calorimetry. The glass transition temperatures (Tg's) of HPMC and HPMC/PEG 400 films were increased in the presence of either talc or titanium dioxide, with the former the more effective Tg enhancer. In contrast, the Tg 's of HPMC/PVA films were virtually unchanged in the presence of the fillers, and this behavior was attributed to the influence of the vinyl backbone of PVA. The Tg's of filled and unfilled HPMC and HPMC/PVA films were lower after storage for 1 year, but the Tg of HPMC/PEG 400 remained unchanged. Phase separation of the mixed polymer systems also occurred following prolonged storage. These phenomena were related to changes in the moisture content and crystal-linity of the films.
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