THERMAL AGING STUDY OF BIODEGRADABLE POLYMER MATERIALS BY DIELECTRIC THERMAL ANALYSIS

Abstract

Two different studies of the thermal aging of polyesters based on lactic and glycolic acids
were compared. Thermal degradation of poly(L-lactic acid) (PLLA), poly(L-lactic acid-co-glycolic
acid) (PLLGA) and poly(DL-lactic acid-co-glycolic acid) (PDLGA) was studied by the dielectric
thermal analysis (DETA). The aging was performed at 37C in vacuum oven. The dielectric features
i.e., dielectric permittivity,, dielectric losses,, and phase lag, tg , were determined by PL-DETA
containing a parallel plate capacitance cell, from the room temperature to 80, 150, and 180  C,
at the heating rates of 2 and 3 Cmin-1. Dielectric scans were obtained at a frequency of 1 kHz and
a.c. signal of 200 mV. Different behavior of PLLA, PLLGA, and PDLGA during degradation was
observed. As the aging of PDLGA proceeds, dielectric losses shift to the lower temperatures,
indicating existence of lower molecular weights.  - T, and tg  - T dependences of PLLGA, as well
as those for PLLA show two simultaneous processes occurring, crystallization and degradation.