Differential scanning calorimetry crystallization temperature determined using

Differential scanning calorimetry (DSC) can be used to determine experimentally the glass transition temperature. The glass transition process is illustrated in Fig. 1.5b for a glassy polymer which does not crystallize and is being slowly heated from a temperature below Tg. Here, the drop which is marked Tg at its midpoint, represents the increase in energy which is supplied to the sample to maintain it at the same temperature as the reference material. This is necessary due to the relatively rapid increase in the heat capacity of the sample as its temperature is increases pass Tg. The addition of heat energy corresponds to the endothermal direction. 

When organic (drug) molecules crystallize from a solvent, the crystal structure is dependent upon the speed of crystallization, temperature, polarity of the solvent, concentration of the material, etc. Since the energy of the crystal affects the (physiological) rate of dissolution and thus the potency and activity of the drug, polymorphism is an important pharmaceutical concern [39]. The most common tool to determine crystal form is differential scanning calorimetry (DSC). Unfortunately, DSC uses small samples and may not represent the bulk of the material. X-ray diffraction is another excellent technique, but quite slow and sometimes difficult to interpret. 

Crystallinity was determined using differential scanning calorimetry. About 5-10 mg of an experimental agent was heated from 25 to 200°C at a heating rate of 20°C/ minute. The sample was isothermed at 200°C for 1 minute and then cooled at a cooling rate of 20°C/minute to ambient temperature. Crystallization data represents peak temperatures of exotherms in the cooling cycle and are summarized in Table 1. 

Dynamic mechanical property (DMP) measurements are used to evaluate the suitability of a polymer for a particular use in sound and vibration damping. Since the dynamic mechanical properties of a polyurethane are known to be affected by polymer morphology (4), it is important to establish the crystallization and melting behavior as well as the glass transition temperature of each polymer. Differential scanning calorimetry (DSC) was used to determine these properties and the data used to interpret the dynamic mechanical property results. 

On cooling from the melt at 120 °C sulfur crystallizes to S/s at a rate too rapid to be determined by differential scanning calorimetry. On storage at ambient temperature the S/s reverts to S (the only allotrope stable under STP conditions). The reversion rate has been measured using differential scanning calorimetry (Figure 2). A 90% reversion rate to S was obtained within 10 hr. 

Differential scanning calorimetry was used to study the non-isothermal crystallization behavior of blends of poly(phenylene sulfide) (PPS) with the thermotropic liquid-crystalline copoly(ester amide) Vectra-B950 (VB) [126], The PPS crystallization temperature and the crystallization rate coefficient increased significantly when 2-50% VB was added. The Ozawa equation was shown to be valid for neat PPS as well as for the blends. The values of the Avrami exponents matched well against those determined previously using isothermal analysis, and they are independent of the concentration of VB. 

The ready availability of differential scanning calorimetry (DSC) and in recent years moduluated DSC have significantly increased the use of the enthalpy of fusion of crystals as a method for crystallinity determination. An illustration of this method was shown for plastic crystals in Chapter 4. The enthalpy of the solid is a combination of components from the amorphous and crystalline regions. The enthalpy at any given temperature His therefore... 

Differential thermal analysis (DTA) and differential scanning calorimetry (DSC) are similar techniques. They measure change in the heat capacity of a sample. These techniques can be used to determine various transition temperatures (T , Tg, T , Tp, etc.), specific heat, heat of fusion, percent crystallinity, onset of degradation temperature, induction time, reaction rate, crystallization rate, etc. A DSC instrument operates by compensating electrically for a change in sample heat. The power for heating is controlled in such a way that the temperature of the sample and the reference is the same. The vertical axis of a DSC temperature scan shows the heat flow in cal/s. 

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