REVERSIBLE AND IRREVERSIBLE HEAT CAPACITY OF POLY(TRIMETHYLENE TEREPHTHALATE) BY TEMPERATURE-MODULATED DIFFERENTIAL SCANNING CALORIMETRY

摘要

The heat capacity of poly(trimethylene terephthalate) has been measured using TMDSC and compared with results obtained from standard differential scanning calorimetry (DSC). Using quasi-isothermal TMDSC, the apparent reversing and non-reversing heat capacities were determined from 220 to 540 K, including the glass transition and melting regions. Using studies as a function of time, truly reversible and irreversible heat effects could be separated. The vibrational heat capacity of the solid and the heat capacity of the liquid and their extrapolations served as base lines for the analysis of the results. Below the melting point, semicrystalline PTT shows, as most other polymers, a reversing heat capacity which is larger than that of the liquid. This is interpreted as a reversible surface melting which does not need to undergo molecular nucleation. The additional time-dependent, reversing contributions at temperatures closer to the melting peak are linked to reorganization and recrystallization (annealing), while the major melting is fully irreversible. The latent heat of polymer melting is thus divided into several important parts, separable by measurement with DSC and TMDSC.