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

Reporting period: 2019-04-01 to 2020-09-30

The performance of any composite material is strongly linked to the adhesion between the host matrix and the reinforcing fibre. Recycled carbon fibres are especially problematic, as they commonly possess less than a quarter of the available surface oxygen compared with virgin fibre , leading to reduced adhesion. The CUSTOMISIZE project aims to improve the interfacial adhesion between recycled carbon fibre (rCF) and polymers (PU, epoxy, PPS and PEKK) and cementitious matrix to obtain composites with enhanced strength, toughness and environmental stability in comparison with state of the art rCFs.
The proposed strategy is the development of specific sizings for different matrices through the incorporation of coupling agents along the fibres (mats, non-wovens and chopped tow). These coupling agents will act by different mechanisms (covalent bond, hydrogen bond, Van der Waals interactions...) to create active points on the CF surface. New approaches, such as Steam Water Thermolysis (SWT), the use of Polyhedral Oligomeric Silesquioxanes (POSS) or Plasma Treatments (Atmospheric or Vacuum), are being used as a novel sizing base to increase rCF-matrix interfacial adhesion. Current sizing technologies (bath coating or spraying) with specific binders for each matrix also are being explored.
After reviewing the state of the art in WP1, it was possible to identify the existing materials used in the production of sizing materials. Also, it was reviewed the different interlinkage mechanisms between recycled carbon fibre and different matrices. The worked carried out in this WP lead to a complete comprehension of the most suitable options to develop different innovative sizing for different matrices (PU, epoxy, PPS and PEKK).

Composites prepared with M21 prepreg were recycled through pyrolysis and steam water thermolysis. M21 prepreg has thermoplastic polymer in its formulation which makes more difficult the recycling process. However, it was possible to perform the recycling of the composites prepared. The chemical composition of the recycled fibres was analyzed by XPS test.
Different sizing were prepared for PU and epoxy matrices. It has been recognized that the application of an epoxy sizing, it is possible to obtain an interphase with a high elastic modulus and low fracture toughness, because of differences in their stoichiometry; this should result in an increment of the stress transfer to the fibre, and preventing an interfacial crack growth.
Araldite LY 3505 is an epoxy resin that was used as sizing material in this study and Aradur 5003-1 is a polyamine based hardener used as curing agent. Different proportions of epoxy and hardener were mixed and dissolved in acetone to prepare the sizing material. Subsequently, oxidized carbon fibres were soaked in the solution for several minutes. Finally, the fibres were dried at 80°C for 30 minutes. Also, amino-terminated silane [3-(2-Aminoethyl) aminopropyl] trimethoxysilane, as a commercially available, cost effective, and bi-amino functional coupling agent was selected as coupling agent.
Surface treated carbon fibre were coated with PEI, to produce a high-temperature resistant sizing for PEKK and PPS. Due to the miscible feature of PEI with PEEK and PPS, the thermoplastic chains can diffuse into the sizing layer at high temperature and pressure. From a practical point of view, the sizing formulation should be easy to use, non-toxic and environmentally friendly.
The polyimide (PI) sizing is adequate for high performance polymers such as PEEK and PPS. Polyimides are polymers made from the reaction between a diamine and dianhydride. In order to have the chemical resistance and thermal stability these molecules need the aromatic structure characteristic of Kapton. In this project, we will start working with pyromellitic dianhydride (PMDAn) and 4,4’-oxydianiline (DAPE).
The different sizings were applied through foulard technique. In the following image, it can be seen one textile after the application of the sizing. In the case of the silane sizing, the application was done in ultrasound equipment (the conditions were explained in the above section).
CUSTOMISIZE will develop tailored and specific sizing approaches for rCF and introduce functional groups to enhance the interlinkage between the rCF and polymeric and cementitious matrices. This will result in improved composite materials with increased mechanical properties. The project will improve the mechanical properties of thermoplastic and thermoset composites by up to 90% and up to 60% for cementitious materials. The overarching objective of the CleanSky Joint Technology Initiative is to speed up technological breakthrough developments leading to greener aircraft and environmental protection. CleanSky supports the environmental goals sets by ACARE to reduce CO2 emissions and NOx by reducing fuel consumption, reduce external noise and stimulate a sustainable product lifecycle. CUSTOMISIZE clearly contributes to these goals by developing innovative sizing approaches for rCF to optimise the adhesion in composites and in turn their mechanical properties.
One of the first initial social impacts of CUSTOMISIZE will be reduction of the landfill waste. Most carbon fibre waste ends up in landfills and still in many countries most of the waste being part of airplane and car body is left in deserted area. CUSTOMISIZE will provide the technology and required process to maximise the use of rCF and contribute to zero plastic landfill concept. The reduction of weight and fuel efficiency will drive the cost of air travel and have a positive social impact Another social impact is in the construction sector. The project will provide solutions to more durable buildings materials that are resistant to corrosion, weather and temperature. The use of CF reinforced cement will reduce the amount of building materials used and reduce the cost of new construction projects resulting in more CUSTOMISIZE able housing.