Viability of recycled fibres extracted from EoL composites

Abstract

Abstract Recycling thermoset-based composites is a technological and economic challenge. The predominating recycling methods (mechanical recycling and pyrolysis) downgrade the fibre properties (length, strength) and are energy-intensive. To avoid downcycling and to ensure economic feasibility, technological solutions need to be developed to enable recycling of long reinforcing fibres that can also be used in demanding applications. Thermochemical recycling, where reinforcing fibres are extracted from the depolymerized matrix, can be considered as an advanced option for recovery of higher quality fibres from EoL composites. Additional steps are required to use these fibres in new composite structures. Thermochemical recycling removes the sizing from the fibre surface making it difficult to handle and resulting in poor fibre-matrix compatibility especially in the case of glass fibres. In this study, we discuss the re-sizing of recycled fibres. We have focused on fibres extracted from glass fibre reinforced composites (GFRPs) from EoL wind turbine blades and carbon fibre reinforced composites (CFRPs) collected from aeronautics industry. We demonstrate the steps for a batch re-sizing process and study the effects of the re-sizing on the properties of composites made of recycled fibres. The interfacial properties are analysed with micro-mechanical testing using the microbond method – both for thermoset and thermoplastic composites – and with tensile tests for thermoplastic composites. Re-sizing significantly eases the handling of the fibres, but the interfacial compatibility is improved only in the case of GFRPs as thermochemically recycled carbon fibres (rCF) exhibit very good interfacial performance even without sizing. This study highlights that with proper recovery and resizing processes, recycled fibres can be viable feedstocks for various applications and – with future improvements on the fibre recovery methods – even approach the applicability of virgin fibres.