Prospective study of lignin-based and recycled carbon fibers in composites through meta-analysis of life cycle assessments

Abstract

Screening the life cycle assessment literature for information and recalculating extracted results was proven useful for identifying environmental challenges and opportunities in new, but related, contexts at early stages of technology development. The method was applied to carbon fiber reinforced polymers, a material of growing importance in industrial applications where a strong and/or light material is needed, such as in aircrafts and road vehicles. Many technology development efforts with the purpose of further improving such composite materials are ongoing, in particular regarding the origin of carbon fibers. Using lignin as a bio-based feedstock and various recycling techniques have been suggested. However, these technologies do not yet exist at a scale that would enable a meaningful life cycle inventory, while the need for environmental guidance is urgent in order to ensure that only the more promising development paths are pursued before lock-in occurs. With a specific focus on the shift to lignin as a feedstock for carbon fibers and on recycled carbon fibers in composites, this article not only illustrates the type of information that can be obtained from mining and refining information from earlier life cycle assessment studies, but it also provides direct guidance on environmental opportunities and challenges specific for carbon fiber reinforced polymers. Thereby, it informs both technology development efforts and environmental assessment efforts. Amongst other things, the analysis reveals that an important factor behind the environmental impact of composites is the energy demand in carbonization of the carbon fibers and that both the shift to lignin-based and to recycled carbon fibers can potentially reduce this environmental impact.However, assessments of both lignin (as an output from a multifunctional process) and recycled carbon fibers (as an output from end-of-life activities) are connected to challenges related to the allocation of environmental impacts in an environmental assessment. Extracting and refining information from the literature proved useful for the specific task but remains to be tested in other fields of emerging technologies.

End-of-Life Recycling Options of (Nano)Enhanced CFRP Composite Prototypes Waste—A Life Cycle Perspective

“…This stage contributes more than 65% and 70% to the climate change impact for the boat and the lever case, respectively, followed by the manufacture stage (approximately 30% for both studied cases). These results are in line with relevant work of the literature [ 92 , 93 , 94 ]. The reference EOL scenario has a minor contribution to climate change, mainly owing to the assumption that composite waste behaves as inert material in a landfill, thus a negligible contribution to methane emission is considered over the years [ 95 , 96 ].…”

Allocation in life cycle assessment of lignin

“…Therefore, there are inherent methodological problems in LCA when assessing its environmental performance, namely, how the environmental burdens of the system should be allocated to lignin and its co-products. It has previously been recognized that the choice of allocation approach in LCAs of lignin is crucial (Secchi et al 2019) because it can strongly affect the environmental performance of the end product, as was also shown for lignin-based carbon fibers by Hermansson et al (2019). However, lignin as a raw material for applications such as carbon fibers or adhesives are emerging technologies still in the development phase.…”

“…For example, Das (2011) uses mass-based allocation, Bernier et al (2013) compare emissions before and after lignin extraction was added to a mill, and Culbertson et al (2016) used system expansion by substitution as well as mass-based and economic allocation. During the work in a previous study on the potential environmental impact of lignin-based carbon fibers, it was found that the allocation method used for the lignin-generating processes could be of great importance for the resulting environmental impact of lignin (Hermansson et al (2019)). In that study, LCA results from different literature sources were explored, applying three different allocation methods to them (mass-based allocation, economic allocation, and a so-called consequential approach (in the present paper referred to as a marginal approach)).…”

“…As the purpose of this study is not to assess which allocation methods are more appropriate for different contexts but to present a wide range of different methods in order to illustrate the possible impact these could have, no specific selections criteria were applied. Most of the employed allocation approaches had been gathered in a previous study, a metaanalysis of already published LCA studies to identify hotspots and identify opportunities and challenges for lignin-based carbon fibers in carbon fiber reinforced polymers (CFRPs) (see Hermansson et al (2019) for more information). In the current study, additional approaches that have been suggested for biorefinery systems were collected from the literature.…”

A review on the recycling of waste carbon fibre/glass fibre-reinforced composites: fibre recovery, properties and life-cycle analysis

“…Surprisingly, studies have focused more on recycling CFRP waste due to its expensive price range and ability to retain maximum mechanical properties after recycling [7,143]. A recent study by Hermansson et al [144] suggested that, in the future, replacing polyacrylonitrile (PAN) with lignin as a raw material for CF will result in lowering the energy use and environmental impact at the time of recycling the waste CFRP.…”