One of the most used fibres in composite materials are carbon fibres. These fibres have excellent properties like light weight, high stiffness, high mechanical strength, high dimensional stability, high corrosion resistance… These properties, in combination with the high price of carbon fibres, makes it interesting to recycle these fibres.
Within the Helacs project research is performed on the recycling of composites used in aircrafts, to recover and recycle carbon fibres and process them into new composites. The recycled carbon fibres will be used as reinforcement in PA6 composites as short fibres or as nonwovens.
Before the short carbon fibres can be used, a sizing is applied on these materials by dipping the fibres in a sizing bath. By improving the sizing formulation, the adhesion between the carbon fibres and the PA6 matrix can be improved resulting in better mechanical properties of the final product. The sizing also improves the processability of the carbon fibres, making it possible to dose them during compounding with the PA6 matrix. Afterwards, short fibre reinforced composites are produced through injection moulding.
Just as with the short fibres, a sizing is applied on the nonwovens via spray application. Via compression moulding, recycled carbon fibre reinforced PA6 composites are made.
These composites are then mechanically characterized via tensile tests, impact tests, ILSS and DMA and compared to short fibre reinforced PA composites made with commercially available carbon fibres or with nonwoven reinforced PA composites without sizing. These results show that the composites made with the sized recycled carbon fibres have similar mechanical properties as the composites made with commercially available carbon fibres and the composites with the sized nonwovens even show an increase in properties of 20% or more.