The various contributions to the apparent, reversing heat capacity measured by temperature-modulated calorimetry (TMDSC) with an underlying heating rate in the temperature range where irreversible transitions with latent heats occur, have been analyzed. Deconvolution of TMDSC data is generally accomplished by approximating the raw experimental data with the first harmonics of the Fourier series of temperature and heat-flow rate. Under certain conditions, this procedure produces misleading results. In the presence of multiple, irreversible transitions within the modulation period, as typically occurs during polymer melting, each irreversible process contributes with its own latent heat to the modulated heat-flow rate. All latent heats absorbed or evolved by the sample produce an increase of the heat-flow-rate amplitude, independently of the direction of latent heat. Since the reversing heat capacity is calculated as the ratio of the amplitudes of heat-flow rate and temperature, the reversing signal is much higher than expected for a single transition. This raises doubts on reports of reversing contributions measured by TMDSC which are determined simply by extraction of the heat-flow rate and temperature amplitudes from the modulated raw data.
Melting of Polymers by TMDSC: Influence of Irreversible Latent Heat to Reversing Heat Capacity
Di Lorenzo ML;
2003
Abstract
The various contributions to the apparent, reversing heat capacity measured by temperature-modulated calorimetry (TMDSC) with an underlying heating rate in the temperature range where irreversible transitions with latent heats occur, have been analyzed. Deconvolution of TMDSC data is generally accomplished by approximating the raw experimental data with the first harmonics of the Fourier series of temperature and heat-flow rate. Under certain conditions, this procedure produces misleading results. In the presence of multiple, irreversible transitions within the modulation period, as typically occurs during polymer melting, each irreversible process contributes with its own latent heat to the modulated heat-flow rate. All latent heats absorbed or evolved by the sample produce an increase of the heat-flow-rate amplitude, independently of the direction of latent heat. Since the reversing heat capacity is calculated as the ratio of the amplitudes of heat-flow rate and temperature, the reversing signal is much higher than expected for a single transition. This raises doubts on reports of reversing contributions measured by TMDSC which are determined simply by extraction of the heat-flow rate and temperature amplitudes from the modulated raw data.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
