Thermal properties and physical ageing of poly (l-lactic acid)
1992; Elsevier BV; Volume: 33; Issue: 13 Linguagem: Inglês
10.1016/0032-3861(92)90440-8
ISSN1873-2291
AutoresAnnamaria Celli, Mariastella Scandola,
Tópico(s)Nanocomposite Films for Food Packaging
ResumoPoly(l-lactic acid) (PLLA) was investigated by differential scanning calorimetry and dynamic mechanical and dielectric spectroscopies. In the dynamic mechanical and dielectric spectra no secondary relaxations were observed below the glass-to-rubber transition (70°C at 3 Hz). The thermal history strongly affects the physical properties of PLLA, inducing changes of crystalline: amorphous ratio as well as large physical ageing effects on the glassy amorphous phase. This latter phenomenon is clearly observed as a consequence of room-temperature storage and develops at a faster rate as the ageing temperature Ta approaches Tg. Ageing experiments carried out at the same undercooling (ΔT = Tg - Ta) on PLLA samples of different molecular weight (M̄v = 5300, 20 000, 691 000) show that a decrease in molecular weight increases the magnitude of the enthalpy relaxation at the glass transition.
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