Differential scanning calorimetry polymer heat capacity

T Hatakeyama, K Nakamura, H Hatakeyama. Smdies on heat capacity of ceUulose and lignin by differential scanning calorimetry. Polymer 23 1801-1804, 1982. 

A3 AIBN c Cp DLS DLVO DSC EO GMA HS-DSC KPS LCST Osmotic third virial coefficient 2,2 -Azobis(isobutyronitrile) Polymer concentration Partial heat capacity Dynamic light scattering Derjaguin-Landau-Verwey-Overbeek Differential scanning calorimetry Ethylene oxide Glycidylmethacrylate High-sensitivity differential scanning calorimetry Potassium persulphate Lower critical solution temperature... 

Most of the physical properties of the polymer (heat capacity, expansion coefficient, storage modulus, gas permeability, refractive index, etc.) undergo a discontinuous variation at the glass transition. The most frequently used methods to determine Tg are differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and dynamic mechanical thermal analysis (DMTA). But several other techniques may be also employed, such as the measurement of the complex dielectric permittivity as a function of temperature. The shape of variation of corresponding properties is shown in Fig. 4.1. 

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. 

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. 

Thermal analysis techniques are designed to measure the above mentioned transitions both by measurements of heat capacity and mechanical modulus (stiffness). Refer to Differential Scanning Calorimetry and Thermogravimetric Analysis. (Source Cheremisinoff, N.P. Polymer Characterization Laboratory Techniques and Analysis, Noyes Publishers, New Jersey, 1996). 

Pyda M, Wunderlich B (2000) Reversible and Irreversible Heat Capacity of Poly(tri-methylene Terephthalate) Analyzed by Temperature-modulated Differential Scanning Calorimetry. J Polymer Sci, Part B Polymer Phys 38 622-631. 

The crystallization and melting behaviors of polymers are conventionally measured by the method of differential scanning calorimetry (DSC). One can obtain the heat flow or compensation power dQ/dt as a function of temperature, which is in principle proportional to the heat capacity of materials Cp and the scanning rate q, as given by... 

Rehable data regarding the heat capacity of amorphous and crystalline phases are available for only a limited number of polymers. The usual techniques for measuring specific heat are differential thermal analysis (DTA) and differential scanning calorimetry (DSC). 

The glass transition temperature is measured using differential scanning calorimetry (DSC) (179,284), by which a polymer sample is heated, and its enthalpic changes are measured in response. The temperature at which the heat capacity of the polymer drops is the glass transition temperature. Dynamic mechanical spectroscopy (DMS) is also used to determine the glass transition temperature. Certain mathematical equations, such as the Fox equation, relate the copolymer composition to the glass transition temperature. 

Enthalpy and Heat Capacity Relaxation. The conventional techniques based on differential scanning calorimetry by which enthalpy relaxation is measured at different cooling and heating rates is discussed elsewhere in the encyclopedia by others. Extensive review of the subject can be foimd in Reference 160. Measurements of heat capacity and entropy of polymers as a function of temperature are well documented and the data can be found in Reference 161. Frequency-dependent heat capacity spectroscopy has been developed (162,163) and apphca-tion to study the local segmental d5mamics of polymers has been made (163). 

Strength of interaction between the carbonyl and the chlorine. Heats of mixing of two polymers, of course, provide a sum of all such energies of interaction. Differential scanning calorimetry measures the changes in heat capacity between the individual components and the blend. 

Two closely related methods dominate the field—the older method, differential thermal analysis (DTA), and the newer method, differential scanning calorimetry (DSC). Both methods yield peaks relating to endothermic and exothermic transitions and show changes in heat capacity. The DSC method also yields quantitative information relating to the enthalpic changes in the polymer (26-28) (see Thble 8.5). 

The thermal stability of the Epiclon-based Pis (Table 1) was evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The Pis exhibit an initial decomposition temperature (IDT) in the range of 270-281°C. The glass transition temperature (Tg) of Pis was probed the by monitoring the heat capacity as a function of temperature. The Tg could be considered as the temperature at which a polymer undergoes... 

As the reader probably knows by now, polymers can exist only in solid or liquid states—and since it is extremely difficult (often impossible) to keep solid and liquid samples at a constant volume when their temperature changes, it is virtually impossible to directly measure C. Thus, differential scanning calorimetry measures Cp of polymers. The DSC signal is closely proportional to the heat capacity of the sample. 

Table 2.8 shows the main features of DSC. Differential scanning calorimetry is the workhorse of the thermal analysis laboratory when it comes to measurements of changes in the heat capacity of a material with temperature. This enables detection and quantification of a wide variety of physical and chemical phenomena, as indicated in Table 2.5. DSC analysis may be applied to polymer products ranging from granules, powders, fibres and Aims to all kinds of injection-moulded parts. DSC is also invaluable in the characterisation of blends and copolymers and...

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