Development of additives for the controlled degradation of polyethylene
File(s)
Author(s)
Parry, Molly
Type
Thesis
Abstract
The resistance of plastics to degradation is part of their appeal, but their environmental persistence is an increasingly pressing issue. The gradual breakdown of polyethylene products can take centuries or millennia. Degradation can be accelerated with exposure to sunlight. The photodegradation process is believed to be initiated by the irradiation of intrinsic carbonyl groups within polyethylene. Advances in the preparation of photodegradable polymers stem from the deliberate inclusion of low concentrations of carbonyl groups within polyethylene.
This thesis explores the targeting of polyethylene analogues with deliberately incorporated regions of oxidation to accelerate and control the weathering process. These synthesised analogues were used as additives for low density polyethylene. Electron paramagnetic resonance spectroscopy was used to underpin radical involving degradation mechanisms.
Polyethylene analogues containing low concentrations of epoxide, diol and dione moieties were successfully synthesised and characterised. These analogues were then blended with polyethylene in varying weight percentages, through twin-screw extrusion. The resultant polymer was pressed into a film and subjected to artificial weathering. The degree of weathering was monitored using gel permeation chromatography to detect changes in molecular weight, and carbonyl index calculations to determine changing levels of oxidation within the sample. Blends of low-density polyethylene with 10% diol additive incorporation achieved a 20% greater decrease in MW in comparison to an additive-free standard over a 28-day weathering period.
To monitor the photoreactivity of diketone containing compounds, Electron Paramagnetic Resonance spectroscopy was utilised. Hexane-3,4-dione was directly irradiated within the resonator cavity using fibre-coupled light-emitting diodes. Using various spin trapping reagents, the reactivity was found to stem from a reversible photoinitiated carbon-carbon cleavage.
Electron Paramagnetic Spectroscopy measurements of irradiated weathered polymer blends showed the presence of paramagnetic species, confirming the increase of photodegradation target sites during weathering. The species were identified using pulsed EPR techniques.
This thesis explores the targeting of polyethylene analogues with deliberately incorporated regions of oxidation to accelerate and control the weathering process. These synthesised analogues were used as additives for low density polyethylene. Electron paramagnetic resonance spectroscopy was used to underpin radical involving degradation mechanisms.
Polyethylene analogues containing low concentrations of epoxide, diol and dione moieties were successfully synthesised and characterised. These analogues were then blended with polyethylene in varying weight percentages, through twin-screw extrusion. The resultant polymer was pressed into a film and subjected to artificial weathering. The degree of weathering was monitored using gel permeation chromatography to detect changes in molecular weight, and carbonyl index calculations to determine changing levels of oxidation within the sample. Blends of low-density polyethylene with 10% diol additive incorporation achieved a 20% greater decrease in MW in comparison to an additive-free standard over a 28-day weathering period.
To monitor the photoreactivity of diketone containing compounds, Electron Paramagnetic Resonance spectroscopy was utilised. Hexane-3,4-dione was directly irradiated within the resonator cavity using fibre-coupled light-emitting diodes. Using various spin trapping reagents, the reactivity was found to stem from a reversible photoinitiated carbon-carbon cleavage.
Electron Paramagnetic Spectroscopy measurements of irradiated weathered polymer blends showed the presence of paramagnetic species, confirming the increase of photodegradation target sites during weathering. The species were identified using pulsed EPR techniques.
Version
Open Access
Date Issued
2025-07-28
Date Awarded
2026-03-01
Copyright Statement
Attribution-Non Commercial-No Derivatives 4.0 International Licence (CC BY-NC-ND)
Advisor
Britovsek, George
Roessler, Maxie
Salehi-Reyhani, Ali
Hill, Gavin
Publisher Department
Department of Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)