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New tailor-made sizing strategies for recycled carbon fibres to improve the mechanical properties of polymeric and cementitious composites

Periodic Reporting for period 2 - CUSTOMISIZE (New tailor-made sizing strategies for recycled carbon fibres to improve the mechanical properties of polymeric and cementitious composites)

Periodo di rendicontazione: 2020-10-01 al 2021-12-31

Composites materials combine two or more components to form a new material that is usually light, strong and durable, so composites have environmental benefits while they are in use. However, considering that are formed by various composite are inherently difficult to recycle. The use of fibre-reinforced polymer (FRP) composites is growing. Almost surely, it will imply more waste that represents a challenge to be recycled. Nowadays, recycled carbon fibres (rCF) are available for reuse however, there is no recycled carbon fibre composite product in the current market. That could be explained considering that, after the recycling process, carbon fibre loses the sizing provided during the manufacturing. It becomes a barrier for recyclability because the compatibility between matrices and carbon fibre is hindered. Compatibility between both, matrix and fibre, is key to achieve high mechanical properties since interfacial adhesion transfer stress from matrix to fibres. The CUSTOMISIZE project bring a solution to the mentioned problem by producing a new family of recycled carbon fibre composite materials with increased mechanical properties. The overall project objective is to resize rCF enhancing the interlinkage between the fibres and polymeric and cementitious matrix. In that sense, a circular economy approach is considered: the sector that generates CF waste is the same to benefit from them.
CUSTOMISIZE project reviewed the state of the art in sizing focused on materials used in aeronautic applications. This state of the art of the sizing materials included carbon fibre structure, properties, and production. However, it focused interfacial elements of the composite system which involve the coupling agent, sizing and adhesion mechanism. In addition, specific carbon fibre surface treatments (oxidative and non-oxidative) and sizings were reviewed for both, polymeric and cementitious matrices.

Afterwards, taking into account the reviewed information new surface treatments and sizings strategies were developed. Comparing the two oxidation treatments (chemical and plasma method) it was demonstrated that plasma oxidation was a better strategy than the chemical oxidation process. Two different sizings were produced for cementitious matrices, i.e. acrylic nanocoating and silanization. Epoxy and PU were considered the thermoset matrices and silanization, amination and POSS sizings were prepared. For thermoplastic matrices (PEKK and PPS) PEI and PI sizings were developed. A complete characterization was carried out, including TGA, DSC, FT-IR, SEM, XPS and water contact angle.

After sizing development, new composite was prepared with re-sized rCF. Polymeric composites included thermoplastic (PEKK and PPS) and thermoset (epoxy) matrices with CF in different forms: woven, non-woven and chopped. Resin Transfer Molding (RTM) and thermal compression were used for woven and non-woven CF. while injection moulding was used for chopped CF composites. A complete characterization was carried out considering key properties, like mechanical properties with iosipescu, ILSS and tensile tests and thermal properties (TGA, DSC) Moreover, SEM was used to analyse fracture surface and characterize CF-matrix interface obtained.
Life Cycle Inventories (LCI) associated to all new CUSTOMISIZE processes have been developed. LCI of CUSTOMISIZE processes allowed to analyse the environmental sustainability profile of the recycled carbon fibres treatments to be used in composites for aircraft (or other) applications compared to conventional processes. The goal and scope of the LCA study, comprehensive description of the CUSTOMISIZE processes and functional unit have been established. From an economic point of view, a Life Cycle Costing (LCC) study have been performed considering the same processes, system boundaries and functional unit as for environmental LCA. Several CUSTOMISZE treatment routes have been defined and CAPEX and OPEX associated to each have been calculated and discussed.

Dissemination activities have been done during the project, such as a poster presented in Ecomondo conference (October 26, 2021) a presentation in Dornbirn (September 15, 2021). Moreover, a flyer was created and distributed in the fairs and workshops where the project was attending.
CUSTOMISIZE results showed that re-sized carbon fibres do not show a significant enhancement in mechanical properties in comparison with unsized fibres. One of the points that CUSTOMISIZE project highlighted is that used CF are quite complex to transform and show some defect after each transformation step before composite re-manufacturing, so achieving high mechanical properties with recycled carbon fibre is challenging. For this reason, to enable carbon fibre reuse and recycle alternative applications should be considered.

The global market size of CF was $3.2 billion in 2020 and the use of carbon fibre-reinforced polymer (CFRP) composites is growing. CUSTOMISIZE project results could impact other less demanding sectors like automotive, packaging, energy, defence, construction, and sports equipment.

CUSTOMISIZE project could contribute to reduce the CF environmental impact considering two different aspects. On the one hand, processes have been designed and developed considering environmental criteria throughout their life cycle: These measures lead to significant environmental benefits such as the reduction of its carbon footprint, resulting from the reduced fuel consumption during the use phase of aircraft-CUSTOMISIZE based. On the other hand, giving a second live to CF providing environmental benefits by avoiding the extraction and processing of virgin raw materials, following a circular economy approach.
Recycled carbon fibre after the application of the sizing
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