An evaluation of the use of modulated temperature DSC as a means of assessing the relaxation behaviour of amorphous lactose.
OBJECTIVE
To evaluate the use of Modulated Temperature DSC (MTDSC) as a means of assessing the relaxation behaviour of amorphous lactose via measurement of the heat capacity, glass transition (Tg) and relaxation endotherm.


METHODS
Samples of amorphous lactose were prepared by freeze drying. MTDSC was conducted using a TA Instruments 2920 MDSC using a heating rate of 2 degrees C/minute, a modulation amplitude of +/-0.3 degrees C and a period of 60 seconds. Samples were cycled by heating to 140 degrees C and cooling to a range of annealing temperatures between 80 degrees C and 100 degrees C, followed by reheating through the Tg region. Systems were then recooled to allow for correction of the Tg shift effect.


RESULTS
MTDSC enabled separation of the glass transition from the relaxation endotherm, thereby facilitating calculation of the relaxation time as a function of temperature. The relative merits of using MTDSC for the assessment of relaxation processes are discussed. In addition, the use of the fictive temperature rather than the experimentally derived Tg is outlined.


CONCLUSIONS
MTDSC allows assessment of the glass transition temperature, the magnitude of the relaxation endotherm and the value of the heat capacity, thus facilitating calculation of relaxation times. Limitations identified with the approach include the slow scanning speed, the need for careful choice of experimental parameters and the Tg shift effect.
Craig
D Q
DQ
The School of Pharmacy, The Queen's University of Belfast, UK. duncan.craig@qub.ac.uk
Barsnes
M
M
Royall
P G
PG
Kett
V L
VL
D002152:Calorimetry, Differential Scanning / Q000379:methods*; D005069:Evaluation Studies as Topic; D007785:Lactose / Q000737:chemistry*; D013696:Temperature
D007785:Lactose