Chemical recycling of carbon fibre-reinforced epoxy composites

Abstract

In this literature review the recent studies conducted on chemical recycling using higher and mild reaction conditions are covered. The goal of this thesis was to conduct a review, collect data and compare different chemical recycling methods reported in the literature for recovering carbon fibres with good mechanical properties from carbon fibre-reinforced epoxy composite material, ensuring a good yield on epoxy resin, while promoting the use of organic or green solvents and catalysts.

The use and possibilities of higher reaction condition chemical recycling including solvolysis and hydrolysis are covered and compared. In the reviewed articles, it was found that by using higher temperatures and pressure with the aid of a catalyst the reaction time could be reduced while maintaining the mechanical properties of the recovered carbon fibre. However, it was found that there is insufficient information about the pathways to recover the resin itself and the used solvent. Multiple studies reviewed in this thesis showed that there are possibilities to use a bench plant while using higher reaction conditions while maintaining the woven structure of the fabric.

The reviewed articles covering the use of mild reaction conditions showed good potential for energy efficiency, but on the other hand, seemed to be using more expensive solvents. Although the solvents, for example, ionic liquids and deep eutectic solvents covered in this thesis, are being considered more expensive, they were stated to be green, sustainable, and possess good reusability. The mechanical properties of the recovered fibres are found to be good in both higher and mild reaction condition methods but mild reaction conditions showed more promise in recovering the degradation products from epoxy resin and reusing the solvents.

This thesis covers the most used and promising methods while introducing novel approaches to the topic. The scale and budget of future laboratory testing will help guide the choosing of method and solvent because it might be the determining factor whether to use more expensive solvents with mild reaction conditions, or high reaction conditions with less expensive solvents. The data collected from future laboratory testing will help guide the optimisation of process parameters.