Differential scanning calorimetry specific heat capacity determined using

Any polymer property that changes with temperature and has different values above and below Tg can be used, in principle, to determine Tg. For example, the change in specific volume, heat capacity, or elastic modulus may be used to measure Tg. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) are two common methods for such determinations. An example of the results of DSC analysis Is presented In Fig. 3.46. It is common for different methods to yield slightly different values for Tg. 

It is seen that the calibration constant disappears, which assumes that it is constant over the experimental conditions. The calculation is carried out using dedicated software. In some circumstances the crucible used for the sample may have to be different from that used for the calibrant. This means that a correction will be required to take into account the difference between the heat capacity of the two crucibles - readily calculated with sufficient accuracy. Measurements can be made at a series of temperatures but are meaningful only within the quasi-steady-state region of the experiment. The specific heat capacity of sapphire has been listed by ASTM in connection with the standard test method E 1269 (1999) for determining specific heat capacity by differential scanning calorimetry. 

E 1269 (1999) Test method for determining specific heat capacity by differential scanning calorimetry E 1354 (1994) Test method for heat and visible smoke release rates for materials and products using an oxygen consumption calorimeter... 

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. 

Specific heat capacity of any material is defined as the amount of energy required to change the temperature of a unit mass of the material by one degree Celsius (or Kelvin). Heat capacity of plastic materials is temperature dependent, and is different for different phases. For example, in the case of semi-crystalline polymers, the heat capacity of the crystalline phase is typically lower than that of the amorphous phase. The most widespread technique used to measure heat capacity of polymers is differential scanning calorimetry (DSC). Alternatively, differential thermal analysis (DTA) can also be used to determine heat capacity. 

Developments in differential scanning calorimetry (DSC) for the characterisation of semicrystalline thermoplastics, including mixed recyclates are discussed. The techniques include stepwise DSC for the accurate determination of specific heat capacity, rapid determination of crystallinity using the Gray-Mathot total enthalpy technique, and analysis of crystallisation kinetics. The techniques show the influence of impurities on the glass transition temperature, crystallinity and crystallisation. 6 refs. 

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