(154ah) Insights into Co-Pyrolysis of Polyethylene Terephthalate and Polyamide 6 Mixture through Experiments, Kinetic Modeling and Machine Learning

The global production of plastics increased from 2 million metric tonnes (MMT) in 1950 to 380 MMT in 2015 [1], leading to a subsequent rise in plastic waste [2]. It has been estimated that only 9% of plastic waste produced globally has been recycled [1]. The major cause of the increase in plastic waste is due to the use of durable goods, containers, and packaging [3]. Among several other polymers, PET and polyamide 6 (PA6) are used in durable goods and packaging due to their mechanical strength, mechanical stabilization, and moisture barrier [4,5]. The durable goods like carpets and rugs contain 15 and 25 wt.% of PET and PA6, respectively [6]. The packaging industry is one of the main consumer of plastics and has a share of 36%, followed by construction (16%) and textiles (15%) [7]. The recycling of multilayer packaging is one of the most challenging issues in the solid waste management sector. This is primarily because multilayer packaging is made up of different polymers and materials like metal oxide coatings (AlO_x or SiO_x) and aluminum foil that are difficult to separate and recycle [8,9]. Pyrolysis is a promising thermochemical recycling technology that can accept single streams as well as a mixed stream of plastics to recycle in a single step without the need for separation unlike mechanical recycling [10]. It involves the thermal decomposition of the polymeric structure in an inert ambiance at moderate temperatures of 400-600 ^oC [11].

In this study, non-isothermal pyrolysis of polyethylene terephthalate (PET), polyamide 6 (PA6), and their mixtures was studied in a thermogravimetric analyzer at different heating rates. The temperature of maximum decomposition (T_max) decreased by 25 – 45 ^oC and 35-55 ^oC for the PET:PA6 mixtures (3:1, 1:1, 1:3) compared to PET and PA6, respectively. The kinetic analysis was initially carried out using isoconversional method. However, the dependency of activation energy on conversion was observed for the co-pyrolysis of PET and PA6 that suggested the occurrence of multi-step reactions in the mixtures. Distributed activation energy model (DAEM) was used in this study to describe the multistep reactions occurring during pyrolysis of PET:PA6 mixtures. In this work, a four-parallel reaction DAEM was developed to describe the pyrolysis kinetics of PET:PA6 mixtures. The mean activation energies (E_o) for PET, PA6, and mixtures varied in the range of 244 – 255, 140 – 215, and 140 – 255 kJ mol^-1, respectively. The mass loss profiles of PET and PA6 mixtures were also modeled using artificial neural network (ANN). Out of 155 ANN models, the best prediction was made by ANN511 with R² > 0.997 for both test and unseen data. The interaction effects observed through TGA experiments and subsequent kinetic analysis were further assessed in terms of product composition using analytical pyrolysis coupled with gas chromatograph/mass spectrometer (Py-GC/MS). Co-pyrolysis of PET and PA6 resulted in the formation of new aromatic compounds with nitrogen-containing functional groups, which were not detected when PET or PA6 were pyrolyzed individually.

References

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