Optimisation of recycling of carbon fibre composites with a supercritical acetone/water solvent

The degradation of a carbon fibre reinforced epoxy resin using an acetone/water solvent mixture supplied in a ratio of 80:20 v/v has been investigated. Conditions ranging from 300 °C, 180 bar to 380 °C, 325 bar have been studied over a processing time of up to 2.5 h. At 300 and 310 °C, sufficient degradation was not observed, while above 340 °C, there was a loss in the weave architecture which would ultimately result in downgrading the material as an effective realignment process is yet to be developed. Therefore, optimum conditions of 320 °C, 195 bar have been identified as suitable for decomposing epoxy resins and recovering clean fibres. Here, a resin removal yield of more than 90 wt.% was achieved and the weave structure was retained. Quadratic trend lines were fitted to the degradation curves suggesting second order reaction kinetics. This was later verified through calculating effective rate coefficients for each temperature studied which were successfully used in an Arrhenius plot. From the data, the pre-exponential factor and activation energy for the process was found to be 61.0 gresin^-1 min^-1 and 317 kJ.mol^-1 respectively. In addition, preliminary analysis of the organic liquid fraction shows a complex mixture consisting of ketones, amines and cyclic compounds. If this mixture can be refined to a sufficient purity, it is possible these compounds can be used elsewhere in the chemical industry resulting in a significant environmental benefit.