Measuring the environmental impacts of carbon fibre:  life cycle assessment

Last summer, I completed a research project in partnership with BGS and the University of Warwick. Based at BGS’s headquarters in Keyworth, Nottinghamshire, I worked alongside the UK Critical Minerals Intelligence Centre (CMIC), gaining first-hand experience of their work and research.

My project focused on using life-cycle assessment (LCA) methods to measure the environmental impacts of a specific product. LCA is a systematic methodology to quantify and evaluate the impacts of a product, service or process throughout its life cycle, from raw material extraction to end of life. The project involved four weeks of LCA training before I conducted my own LCA on a product of my choosing, in this case the composite material carbon fibre (CF).

As a Manufacturing and Mechanical Engineering undergraduate student, I have a particular interest in carbon fibre, for which the UK market is rapidly growing (4.9 per cent compound annual growth rate). With its unique strength-to-weight properties, it’s an important material for innovation in industries such as aerospace, automotives and renewable energy technologies. However, as its use expands, CF recycling becomes ever more essential.

This raises a question: for a high-polymer content material such as CF, how much more environmentally beneficial is recycling over primary production? To answer this, I set out to perform an LCA on both primary production and recycling of CF, to compare and evaluate their consequences on human and environmental health. This was done by first understanding the primary production and recycling processes and then collating the input and output data from secondary sources.

Recycling performed substantially better than primary production across the majority of impact categories, showing large reductions in:

• climate change (91.5 per cent)
• ozone depletion (95.5 per cent)
• acidification (91.4 per cent)
• particulate matter formulation (86 per cent)
• water use (88.7 per cent)
• ionising radiation (99.5 per cent)
• land use (95.9 per cent)
• energy resources (non-renewable) (90.6 per cent)

The category ‘material resources’ saw a 29.7 per cent gain back into the CF life cycle, due to fibre recovery, and ‘human health: carcinogenic’ performed 21.5 per cent worse in recycling compared to initial production, due to the emission of benzene (a known carcinogen) during pyrolysis.

The main contributors of both processes to global warming potential (GWP) through emissions were also evaluated. CF production has a GWP of 31.2 kg CO₂ Eq, caused by:

• feedstock material (52.5 per cent)
• electricity (42.8 per cent)
• natural gas (4 per cent)

The feedstock material evaluated in this assessment was polyacrylonitrile (PAN) fibre, which is the most widely used CF. More specifically, the raw material acrylonitrile was used, which contributes 31.58 per cent to the total GWP of CF production.

Recycling, on the other hand, has a GWP of 2.69 kg CO₂ Eq, contributed to mostly by:

• natural gas (85.7 per cent)
• transport (8.6 per cent)
• electricity (5.7 per cent)

This comparison highlights the importance of recycling CFs for the health of both the environment and the global population. It also recognises areas with the most impact across both production and recycling, to explore potential improvements in future studies.

Potential improvements I have highlighted are:

• alternative bio-based feedstock materials (lignin)    
• net zero energy use
• implementing bio-gas alternatives instead of natural gas
• re-using the byproducts of pyrolysis recycling as fuel back into the process
• implementing alternative recycling operations industrially, such as fluidised bed or chemical recycling

My time researching this topic at BGS has been incredibly rewarding. I have learned so much about the workplace, writing research papers, sustainability and more. I thoroughly enjoyed my experience at BGS’s headquarters; everyone was super friendly and made me feel very welcome.

Thanks go out to Narendra Singh, Gavin Mudd, Evi Petavratzi, Maria Kariuki and the whole CMIC team at BGS for making my placement so rewarding.

Author

Phoebe Brown (undergraduate student)