From our clothes to our oceans; understanding the life cycle of a plastic microfiber

Overview

There are an estimated 5.25 trillion plastic pieces floating in the global oceans (Salvador Cesa, Turra, & Baruque-Ramos, 2017), with approximately 1.5 million tonnes of microplastics polluting the ocean each year, and approximately 35% microplastic pollution is attributed to the fashion industry (Boucher & Friot, 2017). The release of plastic microfibers (MFs) from textiles during laundry represents a significant source of microplastic release into our environment (Browne et al., 2011; Salvador Cesa et al., 2017). Laundering textiles can release 500,000 to over six million MFs for synthetic garments and up to 13 million MFs from cotton garments into the environment per wash. However there are large gaps in our fundamental understanding of the processes by which MFs are released from textiles. This hampers our efforts to mitigate this problem and design methods and processes to reduce MF release into the environment.

This project aims to understand the fundamental mechanisms that cause MFs to become detached and end up in the environment. It will examine the hydrodynamics of MF release in one of our most commonly used textiles — Polyethylene terephthalate (PET). The project will focus on MF detachment events, including the nature of breakage of PET fibers, which is a strong driver of the textiles’ toxicity.

Research objectives
The overall objective of this project is to gain a deeper fundamental understanding of the role of water on MF release from PET during washing and drying procedures. To do this the following work packages will be carried out.
1. Classify PET permeability and different weave structures
2. Design and build a dedicated hydrodynamics test rig (approx. 5cmx5cm cross-section) for visualising the flow through PET at different hydrodynamic pressures and flow speeds.
3. Develop a measurement technique to measure the release of PET fibers in the test rig.
4. Determine how microbial toxicity of the MFs released is affected by the detachment event.

Methodology

The student will survey the most common textile pollutants and classify these textiles (Objective 1).

The student will perform experiments to identify the main culprits in the release of PET MFs into the environment. They will do this by tracking the fibres from pre-release, to release, to eventual capture. In order to achieve this, they will develop a test rig to measure the flow through and MF release from PET of different compositions (fibre length, diameter and textile weaves, Objective 2). Measuring the MF detachment events involves the resolution of flow phenomena around micron-sized filaments, such as that in (Cummins et al., 2018), and this project will utilise a similar methodology.

The student will verify their findings by comparison to existing studies on the release of MFs. These comparisons will include estimating the volume of MF release in different flow conditions and using measurement techniques developed at NCL (Kelly, Lant, Kurr, & Burgess, 2019) (Objective 3).

The student will prepare the MF samples for microbial toxicity testing and will assess toxicity (Objective 4).

Project Timeline

Year 1

Literature review
1. Survey the most prevalent textiles polluting the environment.
2. Assemble a database of textile diagnostics.

Experimental design
1. Develop basic designs of a hydrodynamics test rig to measure MF release and capture.
2. Build hydrodynamics test rig.

3. Assess microbial toxicity

Year 2

Hydrodynamic tests
1. Perform flow diagnostic tests to calibrate the test rig.
2. Measure flow through textiles of different weaves, permeabilities, and MF looseness.
3. Measure MF release: determine the mechanism of release.
4. Measure MF capture downstream.
5. Benchmark rig tests with existing tests in large-scale rigs.

 

Year 3

Perform large parametric studies of how different MF lengths, thicknesses, hydrodynamic pressures etc. affect the release of MFs from textiles. Perform hydrodynamic tests on MF capture technologies.

Year 3.5

Write up and complete PhD thesis.

Training
& Skills

The student will receive significant training in flow diagnostic equipment (Particle Image Velocimetry) and software packages required to analyse the results (e.g., MATLAB or Python). They will also develop skills in statistical analysis (the software package R) and interpretation of data and working with interdisciplinary teams. The student will be supported by the existing PhD students and postdocs based in investigators’ teams at Heriot-Watt and Newcastle Universities. This will create a superb environment to learn new skills and access the experience gained by their peers.

External training: During their project, the student will attend a training course on image analysis, such as a course on ImageJ.

Dissemination of results: The student will learn to present their work at leading scientific conferences such as the annual American Physical Society Division of Fluid Dynamics meeting (USA).

References & further reading

Boucher, J., & Friot, D. (2017). Primary microplastics in the oceans: A global evaluation of sources. In Primary microplastics in the oceans: A global evaluation of sources. https://doi.org/10.2305/iucn.ch.2017.01.en
Browne, M. A., Crump, P., Niven, S. J., Teuten, E., Tonkin, A., Galloway, T., & Thompson, R. (2011). Accumulation of microplastic on shorelines woldwide: Sources and sinks. Environmental Science and Technology. https://doi.org/10.1021/es201811s
Cummins, C., Seale, M., Macente, A., Certini, D., Mastropaolo, E., Viola, I. M., & Nakayama, N. (2018). A separated vortex ring underlies the flight of the dandelion. Nature, 562(7727), 414-418. https://doi.org/10.1038/s41586-018-0604-2
Kelly, M. R., Lant, N. J., Kurr, M., & Burgess, J. G. (2019). Importance of Water-Volume on the Release of Microplastic Fibers from Laundry. Environmental Science & Technology. https://doi.org/10.1021/acs.est.9b03022
Salvador Cesa, F., Turra, A., & Baruque-Ramos, J. (2017). Synthetic fibers as microplastics in the marine environment: A review from textile perspective with a focus on domestic washings. Science of the Total Environment. https://doi.org/10.1016/j.scitotenv.2017.04.172

Further Information

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