Quantitative data differential scanning calorimetry

Based on the structure-related addition schemes for the thermal properties, it should, for example, be possible to quantitatively generate differential scanning calorimetry curves for polymers, copolymers and their mixtures. With easy access to the data bank, it should be possible for thermal analysts to compare their newly measured DSC curves with the computer generated standard curves for on-line analysis of macromolecules. 

The techniques referred to above (Sects. 1—3) may be operated for a sample heated in a constant temperature environment or under conditions of programmed temperature change. Very similar equipment can often be used differences normally reside in the temperature control of the reactant cell. Non-isothermal measurements of mass loss are termed thermogravimetry (TG), absorption or evolution of heat is differential scanning calorimetry (DSC), and measurement of the temperature difference between the sample and an inert reference substance is termed differential thermal analysis (DTA). These techniques can be used singly [33,76,174] or in combination and may include provision for EGA. Applications of non-isothermal measurements have ranged from the rapid qualitative estimation of reaction temperature to the quantitative determination of kinetic parameters [175—177]. The evaluation of kinetic parameters from non-isothermal data is dealt with in detail in Chap. 3.6. 

Differential Scanning Calorimetry (DSC) was used for a long time in the field of process safety [21-23], This is essentially due to its versatility for screening purposes. The small amount of sample required (micro-calorimetric technique) and the fact that quantitative data are obtained, confer on this technique a number of advantages. The sample is contained in a crucible placed into a temperature controlled oven. Since it is a differential method, a second crucible is used as a reference. This may be empty or contain an inert substance. 

Both differential thermal analysis (DTA) and differential. scanning calorimetry (DSC) are concerned with the measurement of energy changes, and as such are applicable in principle to a wider range of processes than TG. From a practical standpoint DSC may be regarded as the method from which quantitative data are most easily obtained. The use of DSC to determine absolute thermodynamic quantities is discussed in Sections 26.2.3.2 and 26.2.4.1. Types of processes amenable to study by these methods are summarized in Table 2. 

Differential scanning calorimetry is not sensitive enough to allow e primaiy reaction to be separated from the secondary reaction in a quantitative manner, such as was the case for the 2.00 stoichiometry. A more species sensitive technique, such as NMR or FTIR, is necessary to discern the individual extents and rates of reaction of the various species. Such data could then be used to verify or refine the currently proposed model. 

The degree of crystallinity can be determined by number of techniques. These techniques involve the measurement of density, volume in dilatometer, ratio of the intensity of absorption bands corresponding to crystalline and amorphous fractions in infrared (IR) spectroscopy, heat of fusion/ crystallization in differential scanning calorimetry (DSC), and area under the diffraction peaks in wide-angle x-ray diffraction (WAXD). The response parameters used to monitor the process of crystallization in these techniques are different and require the data on the properties of the 100% crystalline polymer. These methods are useful for quantitative evaluation of the degree of crystallinity. 

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