Differential scanning calorimetry polymer thermodynamics

Bershstein VA, Egorov VM, Differential Scanning Calorimetry of Polymers, Ellis Harwood, 1994. McNaughton JL, Mortimer CT, Differential Scanning Calorimetry, Thermochemistry and Thermodynamics, Skinner HA ed., Butterworths, London, 1975. 

To determine crystallinity in a semicrystalline polymer, diffraction, thermodynamic, and spectroscopic methods can be used. Diffraction method is mainly used with waxd methods. Thermodynamic methods include dilatometiy, differential scanning calorimetry (dsc), etc, while ir and nuclear magnetic resonance (nmr), and other spectroscopic methods can also be used. 

For many years, the thermodynamic description of macromolecules lagged behind other materials because of the unique tendency of pol5nneric systems to assume nonequilibrium states. Most standard sources of thermodynamic data are, thus, almost devoid of polymer information (1-7). Much of the aversion to include polymer data in standard reference sources can be traced to their nonequilibrium nature. In the meantime, polymer scientists have learned to recognize equilibrium states and utilize nonequilibrium states to explore the history of samples. For a nonequilibrium sample it is possible, for example, to thermally establish how it was transferred into the solid state (determination of the thermal and mechanical history). More recently, it was discovered with the use of temperature-modulated differential scanning calorimetry (TMDSC) that within the global, nonequilibrium structure of semicrystalline polymers, locally reversible melting and crystallization processes are possible on a nanophase level (8). 

Transitions in polymers are rapidly and conveniently studied using differential scanning calorimetry (DSC). Small samples of the polymer and an inert reference substance (one that undergoes no transitions in the temperature range of interest) are mounted in a block with a heater for each and thermocouples to monitor temperatures. The thermodynamic property monitored here is the enthalpy. A servo control system adjusts and measures the power to the heaters to maintain the sample and reference temperatures the same as the sample is... 

In practice, the enthalpy of gasification is rarely calculated because detailed and reliable thermodynamic data for the polymer and its decomposition products are generally unavailable. Direct laboratory measurement of Lg using differential thermal analysis and differential scanning calorimetry has been reported, but Lg is usually measured in a constant heat flux gasification device or fire calorimeter (see under Steady Burning). In these experiments a plot of mass loss rate per unit surface area (mass flux) versus external heat flux has slope 1/Lg where... 

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