Thermal and thermo-oxidative stability of reprocessed poly(ethylene terephthalate)

Abstract

Keywords:Poly(ethylene terephthalate) (PET) Thermal decomposition Thermo-oxidative decomposition Thermogravimetry (TGA) Evolved-gas analysis (EGA) 2D-correlation infrared analysis (2D-IR) Kinetic analysis a b s t r a c t 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 (O 2 ) 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 Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Vyazovkin, Master-Curves and Perez-Maqueda criterion along with Coats-Redfern 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 A n : 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.

Kinetics of poly(ethylene terephthalate) fiber glycolysis in ethylene glycol

“…The thermograms show that significant weight loss between 200 o C and 450 o C, which is attributed to PET polymer degradation process such as a random scission of ester links in the main chain resulting with the formation of different oligomers [22,23]. Further, the maximum decomposition rate of the residual PET fiber will be shifted to lower temperature with the increase of reaction time.…”

Thermal behavior and pyrolytic degradation kinetics of polymeric mixtures from waste packaging plastics

“…Finally, similarly to the findings of the present study, Chowlu et al [29] found that the E a values for the degradation of PP/LDPE mixtures with different compositions shifted from E a values close to those for degradation of PP to the values found for degradation of LDPE with increasing the values of α. By comparing the trends of E a vs. α obtained with the KAS method with those derived by the Vyazovkin method (according to Equation (8)) it is evident that the latter are more scattered, since the integration procedure involves a fewer number of points than in all the integral isoconversional methods (like KAS) [38,58].…”

Continuous post‐polycondensation of high‐viscosity poly(ethylene terephthalate) in the molten state

“…Given that thermal degradation is the largest competitor to the desired polycondensation, massive experimental measurements and theoretical model analysis for the reaction kinetics were presented by numerous different teams, resulting in the activation energy of thermal degradation reactions of approximately 176 ± 2 kJ mol −1 which is marked higher than that of the chain growth reactions . Moreover, notable decrease of the PET quality results caused by thermal degradation include decreased average molecular weight, broadened molecular weight distribution, formation of carboxyl end groups and acetaldehyde, and yellowing of the polymer . In brief, these reactions lead to the reverse transformation of polymer molecular structure, such as chain growth, branching and scission, production of small molecule byproducts and short‐chain oligomers, resulting in poor quality of final products .…”