Green chemistry approaches to the depolymerisation of polyolefin plastic packaging
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Date
2025
Authors
Yap, Forest Tung Jie
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University College Cork
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Abstract
The widespread use of polyolefin plastic packaging has contributed significantly to the global plastic waste crisis, posing severe environmental and economic challenges, making the development of effective plastic degradation strategies imperative for sustainable waste management. This thesis investigates the thermo-oxidative degradation of both virgin (V-) and post-consumer (PC-) low-density polyethylene (LDPE) in acetic acid under relatively mild conditions (120 °C, ambient pressure), evaluating the roles of heterogenous Mn-Fe catalysts, N-Hydroxyphthalimide (NHPI) radical initiator and catalyst-free degradation. Across all experimental conditions PC-LDPE consistently exhibited greater mass loss (~30 %) than V-LDPE (~17 %). Surface-sensitive characterisation by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy revealed a significantly higher degree of functionalisation for PC-LDPE than V-LDPE, attributed to prior oxidation and additives in post-consumer plastics. Qualitative analysis using HPLC consistently showed the presence of formic acid and succinic acid as major degradation products with additional minor signals also observed in the PC-LDPE. The presence of additives and prior processing history have a strong influence on the degradation pathways of LDPE. We further show that heating in acetic acid alone can drive partial thermo-oxidative conversion of PC-LDPE under mild catalyst-free conditions (120 °C, acetic acid). This approach presents opportunities for designing a mild oxidative pretreatment of PC-LDPE that could be coupled to a subsequent harsher chemical upcycling process.
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Keywords
Green chemistry , Polyolefin plastic packaging , Low-density polyethylene , Post-consumer LDPE , Chemical recycling , Thermo-oxidative degradation
Citation
Yap, F. T. J. 2025. Green chemistry approaches to the depolymerisation of polyolefin plastic packaging. MRes Thesis, University College Cork.