@article{ pyda_reversing_2005,
  title = {Reversing and Nonreversing Heat Capacity of Poly(lactic acid) in the Glass Transition Region by {TMDSC}},
  volume = {38},
  issn = {0024-9297},
  url = {http://dx.doi.org/10.1021/ma051611k},
  doi = {10.1021/ma051611k},
  abstract = {A study of the glass transition of an amorphous and a semicrystalline poly(lactic acid) ({PLA}) is performed with adiabatic calorimetry, differential scanning calorimetry ({DSC}), and temperature-modulated {DSC} ({TMDSC}). The reversing, total, and nonreversing apparent heat capacities of samples with different contents of l- and d-lactic acid and with various thermal histories were evaluated. Different modes of {TMDSC} analyses of amorphous and semicrystalline {PLA} were compared to the total heat capacity from standard {DSC}. The enthalpy relaxation and the cold crystallization in the glass transition region are largely irreversible. The melting is largely irreversible, but a 100% reversing fraction is observed at low temperatures from 375 to 420 K, which becomes small inside the major melting peak at about 440 K. From the {TMDSC} of amorphous {PLA}, the combined information on endothermic and exothermic enthalpy relaxation and glass transition were deconvoluted into the reversing and nonreversing components. The glass transition temperature from the reversing heat capacity and the enthalpy relaxation peaks from the nonreversing component shift to higher temperature for increasingly annealed {PLA}. The relaxation times for aging decrease on cooling until the glass transition is reached and then increase. This behavior is linked to cooperativity. All quantitative thermal analyses are based on the heat capacity of the solid and liquid, evaluated earlier with the advanced thermal analysis system ({ATHAS}).},
  number = {25},
  urldate = {2014-09-11TZ},
  journal = {Macromolecules},
  author = {Pyda, M. and Wunderlich, B.},
  year = {2005},
  pages = {10472--10479}
}

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