Characterisation of the glass transition of HPMC using modulated temperature differential scanning calorimetry.

The glass transitional behaviour of HPMC powder and film samples has been studied using modulated temperature differential scanning calorimetry (MTDSC) in order to explore the ability of the technique to detect transitions which involve small changes in heat capacity. HPMC E4M Prem samples were studied in both powder and film form using a TA Instruments MDSC 2920 using a range of pans, modulation amplitudes and underlying heating rates. Moisture contents were measured using a TA Instruments TGA 2950. Studies on HPMC powder demonstrated the greater clarity with which the glass transition, seen at approximately 162 degrees C, may be seen using MTDSC compared to conventional DSC. The practical difficulties associated with casting suitable HPMC films are discussed, with similar results for Tg being found for hermetically sealed pans and pin-holed pans. Increasing the modulation amplitude from 0.212 to 0.5 degrees C improved the signal to noise ratio and increased the magnitude of the measured Tg. Increasing the underlying heating rate from 2 to 5 degrees C/min also improved the signal. The study has outlined several features which need to be considered in association with the measurement of HPMC glass transitions using MTDSC; these include the method of sample preparation, the choice of pans, the modulation amplitude and the underlying heating rate.