Poly(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 ( M ̄v = 5300, 20 000, 691 000) show that a decrease in molecular weight increases the magnitude of the enthalpy relaxation at the glass transition. © 1992.
Celli A., Scandola M. (1992). Thermal properties and physical ageing of poly (l-lactic acid). POLYMER, 33(13), 2699-2703 [10.1016/0032-3861(92)90440-8].
Thermal properties and physical ageing of poly (l-lactic acid)
Celli A.;Scandola M.
1992
Abstract
Poly(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 ( M ̄v = 5300, 20 000, 691 000) show that a decrease in molecular weight increases the magnitude of the enthalpy relaxation at the glass transition. © 1992.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
