Soraia Pimenta

Recycling carbon fibre reinforced polymers for structural applications: Technology review and market outlook

Both environmental and economic factors have driven the development of recycling routes for the increasing amount of carbon fibre reinforced polymer (CFRP) waste generated. This paper presents a review of the current status and outlook of CFRP recycling operations, focusing on state-of-the-art fibre reclamation and re-manufacturing processes, and on the commercialisation and potential applications of recycled products. It is shown that several recycling and re-manufacturing processes are reaching a mature stage, with implementations at commercial scales in operation, production of recycled CFRPs having competitive structural performances, and demonstrator components having been manufactured. The major challenges for the sound establishment of a CFRP recycling industry and the development of markets for the recyclates are summarised; the potential for introducing recycled CFRPs in structural components is discussed, and likely promising applications are investigated.

On longitudinal compressive failure of carbon-fibre-reinforced polymer: from unidirectional to woven, and from virgin to recycled

Modelling the longitudinal compressive failure of carbon-fibre-reinforced composites has been attempted for decades. Despite many developments, no single model has surfaced to provide simultaneously a definitive explanation for the micromechanics of failure as well as validated predictions for a generic stress state. This paper explores the reasons for this, by presenting experimental data (including scanning electron microscopic observations of loaded kink bands during propagation, and brittle shear fracture at 45° to the fibres) and reviewing previously proposed micromechanical analytical and numerical models. The paper focuses mainly on virgin unidirectional (UD) composites, but studies for woven and recycled composites are also presented, highlighting similarities and differences between these cases. It is found that, while kink-band formation (also referred to in the literature as microbuckling) is predominant in UD composites under longitudinal compression, another failure mode related to the failure of the fibres can be observed experimentally. It is also shown that the micromechanics of the failure process observed in UD composites is similar to that in other fibre architectures, hence encouraging the adaptation and application of models developed for the former to the latter.

Fibre failure modelling

Abstract Fibre-dominated tensile failure in composites is a complex phenomenon governed by the statistical distribution of fibre strengths and the micromechanics of stress-transfer in the neighbourhood of fibre breaks. This chapter provides an overview of classical and state-of-the-art material models to simulate the fibre-dominated tensile failure process in unidirectional composites, and to predict the tensile strength and fracture toughness of these materials, as well as the associated size effects. The relevance of such material models for the simulation of composite components is discussed, and it is demonstrated that the correct representation of size effects at the material scale is fundamental to accurately predict the response of more complex structures.

Recycling of Carbon Fibers

Abstract The use of carbon fibers has been growing exponentially, prompting the development of sustainable recycling routes for the carbon fiber reinforced polymer (CFRP) waste generated. Mechanical and thermochemical (e.g. pyrolysis) fiber reclamation processes are reviewed; it is shown that, under optimized conditions, most processes can recover fibers with virtually no degradation of mechanical and electrical properties. Reintroducing the fibers into new composites is challenging because of their unstructured form, thus requiring extra processing; nonetheless, the mechanical properties of recycled CFRPs compete with those of glass composites, aluminum and even virgin CFRPs. It is expected that recycled composites will be applied mostly in nonsafety critical components for the transports industry, in which case life cycle assessment suggests that recycling is greener than landfilling or incineration; nonstructural applications are also reviewed. Some of the challenges ahead—namely establishing a sound CFRP recycling chain, understanding the complex response of recycled composites and optimizing industrial scale processes—are discussed.