Recycling of carbon fibre reinforced composites by supercritical solvolysis routes

Abstract

The recycling of composite materials is rapidly gaining importance in industry. To find an appropriate and efficient method to recycle Carbon Fibre-reinforced Composites (CFRP) with a thermoset epoxy matrix via solvolysis, several tests were performed. In ambient pressure and low temperature conditions, as well as in higher temperature regimes under subcritical, vapour pressure conditions three different types of specimens were tested with various solvents and catalysts. Neat-epoxy specimen cured with Anhydride and Amine hardener, as well as unidirectional CFRP plates stacked from pre-preg plies and cured in an autoclave. Their mass uptake and degradation was used to compare the different solvent systems in both swelling experiments. After determining 1-Propanol catalysed with Potassium hydroxide as the most efficient, the selected combination was used under supercritical conditions in a semi-continuous flow type reactor. The design and installation of this facility was part of this research project. The retrieved recyclate of the sub- and supercritical experiments were examined by scanning electron microscopy. The recycled fibres from the supercritical experiment were used to manufacture specimen with new epoxy matrix based on Anhydride hardener and comparing their tensile strength to the virgin pieces as well as the matrix fibre adhesion in short beam shear tests. Furthermore, a energy efficient, subcritical method was developed to recycle prepreg cutoffs in order to use them in random oriented short fibre composites.