Abstract
Carbon fibers have been widely used in composite materials, such as carbon fiber-reinforced polymer (CFRP). Therefore, a considerable amount of CFRP waste has been generated. Different recycling technologies have been proposed to treat the CFRP waste and recover carbon fibers for reuse in other applications. This study aims to perform a life cycle assessment (LCA) to evaluate the environmental impacts of recycling carbon fibers from CFRP waste by steam thermolysis, which is a recycling process developed in France. The LCA is performed by comparing a scenario where the CFRP waste is recycled by steam-thermolysis with other where the CFRP waste is directly disposed in landfill and incineration. The functional unit set for this study is 2 kg of composite. The inventory analysis is established for the different phases of the two scenarios considered in the study, such as the manufacturing phase, the recycling phase, and the end-of-life phase. The input and output flows associated with each elementary process are standardized to the functional unit. The life cycle impact assessment (LCIA) is performed using the SimaPro software and the Ecoinvent 3 database by the implementation of the CML-IA baseline LCIA method and the ILCD 2011 midpoint LCIA method. Despite that the addition of recycling phase produces non-negligible environmental impacts, the impact assessment shows that, overall, the scenario with recycling is less impactful on the environment than the scenario without recycling. The recycling of CFRP waste reduces between 25 and 30% of the impacts and requires about 25% less energy. The two LCIA methods used, CML-IA baseline and ILCD 2011 midpoint, lead to similar results, allowing the verification of the robustness and reliability of the LCIA results. The recycling of composite materials with recovery of carbon fibers brings evident advantages from an environmental point of view. Although this study presents some limitations, the LCA conducted allows the evaluation of potential environmental impacts of steam thermolysis recycling process in comparison with a scenario where the composites are directly sent to final disposal. The proposed approach can be scaled up to be used in other life cycle assessments, such as in industrial scales, and furthermore to compare the steam thermolysis to other recycling processes.
Highlights
The use of carbon fibers has widely increased in a number of applications such as aerospace, wind energy, automotive, sporting goods, and other industrial fields, due to their excellent characteristics like high mechanical properties, low weight, high corrosion resistance, temperature tolerance, and low thermal expansion (Wang et al 2016; Ma et al 2016; Industry Experts 2013)
In a life cycle assessment (LCA), the differences below 20% are not sufficient to conclude with certainty because it is always necessary to consider the uncertainties of the input data and impact assessment methods
As previously demonstrated with the CML-IA baseline life cycle impact assessment (LCIA) method, the materials used for the construction of the cutting machine and the steam thermolysis reactor, present in the scenario with recycling, are an important source
Summary
The use of carbon fibers has widely increased in a number of applications such as aerospace, wind energy, automotive, sporting goods, and other industrial fields, due to their excellent characteristics like high mechanical properties, low weight, high corrosion resistance, temperature tolerance, and low thermal expansion (Wang et al 2016; Ma et al 2016; Industry Experts 2013). More than 97% of carbon fiber produced is processed into composite materials, such as carbon fiber-reinforced polymers (CFRPs) (Jahn 2013). These composites have acquired great importance in major industrial sectors, mainly in the aerospace and automotive industry. As composite materials are very difficult to fractionate into elemental components, the waste has been mainly disposed in landfills or incinerated (Morin et al 2012). These techniques have became strictly regulated by the environmental legislations. In Europe, waste directives have limited landfill disposal and imposed that 95% of average weight of end-of-life vehicles manufactured after January 2015 must be recycled (EU 2000/53/EC)
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