[Image above] Interior shot of an Audi RS6+ with a carbon fiber composite steering wheel. A new prospective life cycle assessment suggests certain technological developments could lead to carbon fiber composites with lower environmental impact than glass fiber composites. Credit: Sam te Kiefte, Unsplash
When Owens Corning first introduced glass fiber-reinforced polymer products to the marketplace in the 1930s, they likely had no idea how massive the fiber-reinforced polymers industry would grow over the following century—a recent Industry Experts market report valued the glass fiber composite market at $9.7 billion in 2021.
While glass fiber composites are well established—they serve as insulation, rust protection, slip resistance, and defense against chemical corrosion in numerous industries—carbon fiber-reinforced polymers have become a major player in the industry as well, thanks to improved fabrication methods leading to reduced production costs.
Automobile manufacturers have explored using both glass fiber and carbon fiber composites as replacements for metals and alloys in cars to reduce vehicle weight and thereby fuel consumption. However, while carbon fiber composites are lighter than glass fiber composites, thus giving them an edge in achieving this goal, it does not automatically mean these composites will have an overall lower environmental impact throughout a vehicle’s life cycle.
In 2019, an environmental life cycle assessment found that replacing conventional materials with carbon fiber composites increases life cycle energy use in more than half of the compiled cases. This increase is due primarily to the energy-intensive carbon fiber production process, which “is responsible for more than 50% of the [carbon fiber composite] climate impact and energy use in all studies but one,” the assessment reported.
Transitioning to a bio-based raw material in carbon fiber production or recovering the fibers from recycled composites could potentially decrease the environmental impact of carbon fiber composites, as well as using microwave heating when producing the fibers. However, further studies are needed to assess if and under which conditions the use of carbon fiber composites in vehicles could have a lower environmental impact.
A new open-access life cycle assessment published in Resources, Conservation and Recycling begins to answer these questions. The authors of the study come from Chalmers University of Technology in Sweden and include the same researchers who conducted the 2019 environmental life cycle assessment. Like with the previous assessment, they took a “prospective” approach to this study.
Prospective life cycle assessments are future-oriented assessments that often use scenario methods to develop plausible futures for assessment because the emerging technologies are not yet implemented at an industrial scale. These assessments can entail exploring not only various considered or conceivable technical changes to a device (foreground considerations) but also changes to surrounding systems, such as energy systems and markets of different materials (background considerations).
For the new study, the authors assessed the use of lignin-based carbon fibers for composites and microwave heating technologies because this study is a part of the Lignin Based Carbon Fibers for Composites project. They also assessed the effect of recycling composites and recovering fibers due to the promising results reported in their earlier study.
To assess these different technology development routes both separately and in combination, the authors developed explorative scenarios based on the method used by Langkau and Erdmann (2021), who assessed the environmental impacts of the future supply of rare earth metals. The table below gives the three scenarios that were ultimately identified as most plausible and used in the final assessment.
Regarding the scenarios, the authors note that they considered only the most extreme situation for all scenarios. “This choice was based on the argument that the balance between technologies is hard to predict, so for clarity reasons, when presenting the results, this assessment is binary in the sense that it is either 100% or 0% of the different sub-scenarios. … In the future, there would of course be a mix, with some sub-scenarios dominating,” they explain.
Table 1. The three constructed scenarios for the assessment. *Only influences carbon fiber-reinforced polymers; all other developments influence both carbon fiber and glass fiber composites. Credit: Hermansson et al., Resources, Conservation and Recycling (CC BY 4.0)
| Parameter settings in foreground system | Parameter settings in background system | |
| Scenario 1: Bioeconomy | – Fibers are produced from bio-based raw materials* – Fibers are produced using microwave heating* – Composites are sent to landfill | – Price of lignin increases* – Energy mix transitions towards being fossil-carbon lean – Composites are used in a battery electric vehicle – There is legislation to reduce extraction of fossils from the ecosphere |
| Scenario 2: Circular economy | – Fibers are produced using fossil-based raw materials – Fibers are produced using conventional technologies – Composites are recycled and materials recovered | – Price of lignin remains the same* – Energy mix stays constant – Composites are used in vehicle with internal combustion engine – There is legislation to promote recycling and recovery of materials; end-of-life recycling approach |
| Scenario 3: Circular bioeconomy | – Fibers are produced using bio-based raw materials* – Fibers are produced using microwave heating* – Composites are recycled and materials recovered | – Price of lignin increases* – Energy mix transitions towards being fossil-carbon lean – Composites are used in a battery electric vehicle – There is legislation to reduce extraction of fossils from the ecosphere; cut-off allocation approach |
Based on the assessment, the authors conclude that recycling composites with recovery of fibers is the route that alone shows the greatest potential for lowering the environmental impact of carbon fiber composites. Nonetheless, all three different futures showed that carbon fiber composites demonstrate “great potential” to have a lower environmental impact than glass fiber composites. However, this result is highly dependent on assumed developments in the background considerations, such as a high price of lignin and increased incentives for recycling.
The authors note that because these findings are based on a prospective assessment, “any results presented in this paper should merely be viewed as an indication about what could happen under different technological and societal developments and be used as guidance for, e.g., future material development studies.”
The open-access paper, published in Resources, Conservation and Recycling, is “Can carbon fiber composites have a lower environmental impact than fiberglass?” (DOI: 10.1016/j.resconrec.2022.106234)