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High performance products for aeronautics, aerospace, military, and sports applications are manufactured manually by hand lay-up techniques for small-scale production. Here mainly carbon fibre and epoxy matrices are used in form of pre-impregnated reinforcement, named prepregs. Curing is made in autoclaves and the final material, carbon fibre reinforced plastic, is designated CFRP. Examples of products are the wings in some combat aircraft, where composite materials account for 30% of the total weight. Many examples can also be found in civil aircrafts. For example in the new Airbus A380 the fuselage is manufactured in carbon fibre composite. Totally 25% of this aircraft’s structure is in composite material of which 22% is based on carbon fibre. A primary concern about the possibility to mechanically recycle CFRP is the availability of a suitable grinding process.


Fig. 1 - Diagram for characterising polymer materials and polymeric compositesfor granulation through grinding (Reftman, 2002).

Through earlier investigations the grinding process in a granulator with cutting knifes has been well documented for polymeric materials and FRP-composites (Reftman, 2002). A scheme for optimising the grinding process is developed, see Figure 1. The investigated materials, SMC, CFRP, GMT, PP/Flax are grouped according to three fragmentation types. These are defined from the left to the right on the x-axis as brittle – type I, between brittle and tough – type II, tough – type III. The fragmentation type is assessed through the “brittleness number” (Cs) determined by the toughness of the material. The y-axis describes the cutting edge load extending from low to high in form of the cutting resistance (Fs) which is coupled to the shear strength of the material.

References
Reftman, T. (2002) ”Granulerbarhet och återvinning av polymerer”, Avdelningen för mekanisk teknologi och verktygsmankiner, ISBN 91-628-5231-0, LUTMDN/(TMMV-1053)/1-289/(2002).