A novel powder sample holder for the determination of glass transition temperatures by DMA

Abstract: The use of a new sample holder for dynamic mechanical analysis (DMA) as a means to characterise the T g of powdered hydroxypropyl methyl cellulose (HPMC) has been investigated. A sample holder was constructed consisting of a rectangular stainless steel container and a lid engineered to fit exactly within the walls of the container when clamped within a TA instruments Q800 DMA in dual cantilever configuration. Physical mixtures of HPMC (E4M) and aluminium oxide powders were placed in the holder and subjected to oscillating strains (1Hz, 10Hz and 100Hz) whilst heated at 3°C/min. The storage and loss modulus signals showed a large reduction in the mechanical strength above 150°C which was attributed to a glass transition. Optimal experimental parameters were determined using a design of experiment procedure and by analysing the frequency dependence of T g in Arrhenius plots. The parameters were a clamping pressure of 62kPa, a mass ratio of 0.2 HPMC in aluminium oxide, and a loading mass of either 120mg or 180mg. At 1Hz, a T g of 177±1.2°C (n =6) for powdered HPMC was obtained. In conclusion, the new powder holder was capable of measuring the T g of pharmaceutical powders and a simple optimization protocol was established, useful in further applications of the DMA powder holder. [Copyright &y& Elsevier]