Recycling of composites by recovering carbon fibres of cured prepregs, and their re-use in hybrid laminates
by Andrea Fernández Gorgojo
The applications of composite materials are rapidly growing in several sectors. For example, in the aeronautical sector, composites can account for up to 50% of the weight of a modern aircraft. At the same time, several related European laws have been passed to minimize the environmental impact of composite structures (EU 2000/53/EC, End of life vehicles), as well as to make rational use of landfills (EU 1999/31/EC). With environmental concerns becoming an increasingly influential topic, recyclability of composite materials is a key issue. The objective of this research is the study of the recycling techniques of carbon fibre composites with thermoset polymer matrix, in order to obtain recycled fibres with similar properties to the original ones. In this way, the fibres could be reused in new composites of recycled carbon fibres, or together with glass fibres in the manufacture of new hybrid composite materials. By this latter hybridization, materials with properties far superior to the usual glass fibre reinforced polymers (GFRP) would be obtained, but at much lower cost than the original carbon fibre reinforced polymers (CFRP). Therefore, this recycling and reprocessing strategy provides great economical incentives.
The main objective this research is to study and optimize the recyclability of cured carbon fibre/epoxy prepregs for use in hybrid composite materials. Besides, different hybridization technologies will be analysed. These results are expected to be implemented in the automotive, wind energy, construction and railway sectors and even in the aeronautics sector.
The principal method use to recycle fibres is the pyrolysis in a controlled atmosphere reactor followed by an oxidation. In order to optimize the recycling process, an evaluation of its different parameters has been carried out, taking into account the surface, elasticity, tensile strength, fracture toughness and density/volume ratio of the recycled fibres. The so obtained carbon fibres showed similar properties to virgin ones, with a loss of less than 20% of the original tensile strength. This study was carried out during the first year of the research.
The second part of the research is based on the manufacture of new composite materials, consisting only of recycled fibres together with other types of virgin fibres. The fabrication process and obtained materials will be evaluated in terms of microstructure -for example, in-situ analysis of the constituents (mainly fibre/matrix interface)- and mechanical properties of plies and laminates.