Thermal History and Crystallinity

The effect of previous heat treatments (thermal history) can significantly affect the shape of the DSC curve for semicrystalline materials. This can make comparisons difficult, unless a similar thermal history has been applied to both samples. This effect is well known for polymers, fats, and waxes and so can become an issue when looking at suspensions or polymer-modified drug delivery systems. 

For long-chain hydrocarbons, the amount of order or crystallinity will depend on how slowly the sample has been cooled from the melt back down to room temperature. For samples that are cooled quickly, there is less time available for the sample to assemble into ordered structures. The result will be a material with a smaller fusion endotherm when it is subsequently reheated. If the sample is cooled slowly, there is more time for it to crystallize. Here, the result will be a material with a larger fusion endotherm on reheating. 

FIGURE 2.2 DSC trace for amorphous salbutamol sulfate, showing the glass transition, recrystallization peak, and melting/degradation peak. 

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