Melting of Polymers by TMDSC: Influence of Irreversible Latent Heat to Reversing Heat Capacity

摘要

The various contributions to the apparent, reversing heat capacity measured byrntemperature-modulated calorimetry (TMDSC) with an underlying heating rate in therntemperature range where irreversible transitions with latent heats occur, have been analyzed.rnDeconvolution of TMDSC data is generally accomplished by approximating the rawrnexperimental data with the first harmonics of the Fourier series of temperature and heat-flowrnrate. Under certain conditions, this procedure produces misleading results. In the presence ofrnmultiple, irreversible transitions within the modulation period, as typically occurs duringrnpolymer melting, each irreversible process contributes with its own latent heat to thernmodulated heat-flow rate. All latent heats absorbed or evolved by the sample produce anrnincrease of the heat-flow-rate amplitude, independently of the direction of latent heat. Sincernthe reversing heat capacity is calculated as the ratio of the amplitudes of heat-flow rate andrntemperature, the reversing signal is much higher than expected for a single transition. Thisrnraises doubts on reports of reversing contributions measured by TMDSC which arerndetermined simply by extraction of the heat-flow rate and temperature amplitudes from thernmodulated raw data.