Reversing and nonreversing contributions to polymer melting

Temperature-modulated differential scanning calorimetry allows the measurement of the total heat capacity, the so-called reversing heat capacity, and their difference, the so-called nonreversing heat capacity. There is an ongoing controversy about the meaning of these quantities in the melting region of polymers. To better understand the contributions to the reversing heat capacity, the results from model calculations are compared with experimental results for different semicrystalline polymers under different experimental conditions. This allows a more precise distinction between reversing and nonreversing contributions to the total heat capacity in a temperature-modulated differential scanning calorimetry scan measurement. A time dependence of the melting process is observed for poly(ethylene terephthalate) and bisphenol. A polycarbonate. For an ethylene-octene copolymer the temperature dependence of the fraction melting reversingly is obtained. The model, which does not take any time dependence into account, also predicts the contribution from the nonreversing melting to the phase angle. Limitations and possible extensions of the model are discussed.