Overview

By 2015, humans had generated 8.3 billion metric tons of plastics, 6.3 billion tons of which had already become waste. Of that waste total, only 9 percent was recycled, 12 percent was incinerated and 79 percent accumulated in landfills or the natural environment. The quantity of plastics on our planet will continue to grow, reaching 40 billion tons by 2050. Plastics is now a major feature of the changed, Anthropocene, state of our planet.

Plastics are lightweight, and tend to float in our oceans. Plastic debris in the marine environment has become an issue of global concern. While media attention has been drawn to macro-plastic debris accumulating in oceanic gyres and on coasts, or causing damage to wildlife, the insidious effects of micro-plastics go relatively unnoticed, as largely unseen, small particles (<1 mm, but as small as 5um) have become ubiquitous in the marine environment over just a few decades. Moreover, it is becoming apparent that this may have consequences for marine ecosystems and humans.

Most plastic is non-biodegradable and will remain in the environment for hundreds, or thousands of years. There is an urgent need, therefore, to understand how the plastics degrades, what the major degradation products are. This will also allow to access how plastic degradation will impact on the natural environment.

Figure 1: Plastic bottles and garbage waste from a village in Timor-Leste wash on the shores of a river and then spill into the sea. UN Photo/Martine Perret.

Methodology

The degradation of plastics requires destroying polymer structures, creating smaller molecules, free radicals. Here we will detect free radicals using cavity ring-down spectroscopy (CRDS) technique, which is highly sensitive and can detect free radicals ejected from plastics when plastics is illuminated by UV light.

A sunlight simulator will be employed as the radiation source for plastic samples, and two sets of experiments will be performed: 1) Typical plastics for packaging, e.g., bottles, shopping bags (polyethylene) and bottle caps (polypropylene), will be studied under vacuum, which will be illuminated by UV and high-energy visible (UV-HEV) light. This is to understand the underlying chemistry of polymer degradation. 2). The same set experiments will be performed in air, allowing the free radicals to react with atmospheric molecules such as N2, O2 and H2O, and the reaction products will be detected by CRDS. This will allow the identification of toxic species such as ketones, and their contribution to air pollution and environmental hazards.

 

Training and Skills

CENTA students are required to complete 45 days training throughout their PhD including a 10 day placement. In the first year, students will be trained as a single cohort on environmental science, research methods and core skills. Throughout the PhD, training will progress from core skills sets to master classes specific to CENTA research  themes. 

The student will receive wide-ranging training in this project, including laser spectroscopy, CRDS technique, ab initio calculations, etc. Targeted training will be given in spectroscopy and computation, especially with respect to free radical detection and spectroscopy analysis. The student will be based in the NanoChemistry Group and thereby benefit from the group’s extensive expertise in spectroscopy. Facilities for the work at UoL are excellent and include an extremely well-equipped open-plan laboratory. Specific to the proposed research are state-of-the-art laser facilities and a CRDS apparatus, which are fully functional.

Timeline

Year 1: Initially the project will combine theory with practice. The student will be trained to do computational chemistry using Gaussian, and will start to calculate optical spectra of free radicals such as CH3, CH2O and OH. He/she will also design and construct a free radical detection cell for plastic samples, which will be incorporated into the existing CRDS apparatus. Meantime, the student will be trained to operate our pulsed OPO lasers. Follow-on experiments will be performed to optimise the cell design, the illuminating light, and to demonstrate the performance of the apparatus.

Year 2: Different types of plastic samples for packaging will be investigated under vacuum, which will be illuminated by a sunlight simulator. This is important to detect which free radicals are produced when plastics breaks down under sunlight. By this procedure, we can also estimate the potential health impact of plastic emissions to the environment and their contribution to air pollution.

Year 3: The Year 3 project will focus on the environmental influence to the breakdown of plastics. Essentially, this will study the secondary reactions between plastics and the molecules existing in ambient condition. In particular, we will examine how the temperature and moisture will influence the degradation product of plastics.

Partners and collaboration (including CASE)

We already have collaborations with several industrial partners in relevant areas such as polymer degradation under UV radiation. A specific project is to protect the indoor polymer coating by decelerating the degradation of polymers. This CENTA project looks at polymer in a different angle: the focus is to study the chemistry of plastic breakdown, how the natural environment may influence this process, and what the degradation products are. Clearly, this project is related to the design of novel degradable plastics, and we intend to cultivate this interest to generate commercial sponsorship and to explore converting the project to a CASE studentship.

Further Details

Potential applicants are welcome to discuss the project informally and obtain further information from the project supervisors:

Dr Shengfu Yang, Department of Chemistry, University of Leicester, Leicester LE1 7RH; sfy1@le.ac.uk

Prof. Sarah Gabbott, Department of Geology, University of Leicester, Leicester LE1 7RH; sg21@le.ac.uk