Thermal and chemical treatments of recycled carbon fibres for improved adhesion to polymeric matrix

The aim of this study is the characterization of recycled carbon fibres, in view of their potential application in long-fibre reinforced thermoplastic composite. The fibres were obtained from epoxy matrix composite panels, applying a patented process that includes the pyrolisis of the matrix followed by an upgrading of the fibres. Then, recycled fibres were further subjected to thermal and acid treatments in order to modify their surface morphology and chemistry. Scanning electron microscopy and energy dispersive spectrometry were used to characterize the morphological and compositional changes of the fibre surface. The fibres were characterized in terms of mechanical properties and adhesion to an epoxy matrix. The fibres treated by thermal processes at high temperatures (600°C) were shown to be too severely damaged, making them unsuitable for the production of fibre-reinforced composites. A thermal treatment at lower temperatures (450°C) involved a very limited damaging without any evident chemical modification of the fibre surface, which in turn involved a limited increase of the adhesion properties to an epoxy matrix. Chemical treatment by nitric acid caused a very limited damage of fibres, coupled with a significant modification of surface chemistry, which in turn involved a further increase of the fibre/matrix adhesion properties.