Abstract
An exhaustive assessment of the behaviour of virgin and mechanically reprocessed poly(ethylene terephthalate)
(PET) facing thermal and thermo-oxidative decomposition processes is presented in this work, as
an approach for the energetic valorisation of post-consumer PET goods. Multi-rate linear-non-isothermal
thermogravimetric (TGA) experiments under inert (Ar) and reactive (O2) conditions were performed to
virgin PET and its recyclates in order to simulate the thermal behaviour of the materials facing pyrolysis
and combustion processes. The release of gases was monitored by evolved gas analysis of the fumes of
the TGA experiment, by in-line Fourier-transform infrared (IR) analysis, with the aid of 2D-correlation IR
characterisation. A kinetic analysis methodology, consisting in the combination of six different methods
(namely FlynnWallOzawa, KissingerAkahiraSunose, Vyazovkin, Master-Curves and Perez-Maqueda
criterion along with CoatsRedfern equation) was applied. Its validity for being used for both constant and
variable kinetic parameters was discussed. The kinetic model that described both thermal and thermooxidative
decompositions of PET and its recyclates was of the type An: nucleation and growth of gas
bubbles in the melt. Novel parameters and functions were proposed to characterise the thermal stability
along the reprocessing cycles, as well as the variation of the activation energy and the pre-exponential
factor during thermal and thermo-oxidative decompositions. The reliability of a simplified kinetic triplet
with constant activation parameters was suitable only under thermal decomposition. The usability of
PET after reprocessing showed a threshold in the thermal performance from the second recyclate on.
During thermal and thermo-oxidative processes, reprocessed PET behaved similarly to virgin PET, and
thus current energetic valorisation technologies could be assimilable for all materials.
