Development of a closed-loop recycling process for discontinuous carbon fibre polypropylene composites

Abstract

In this study the effects of a closed-loop recycling methodology are evaluated for degradation using a discontinuous carbon fibre polypropylene (CFPP) composite material. The process comprises two fundamental steps, reclamation and remanufacture. The material properties are analysed over two recycling loops. For neat polypropylene, the molecular weight analysis indicates evidence of minimal matrix degradation that does not affect the material behaviour, as demonstrated by the shear tests. CFPP specimens show no decrease in mechanical properties over repeated loops, the final specimens show an increase of 26 % and 43 % in ultimate tensile strength and ultimate strain, respectively. These are attributed to cumulative matrix residue on the fibre surface after reclamation and subsequently increased fibre-matrix adhesion. The improvement of CFPP properties and insignificant variability in the tensile properties and molecular weight distribution of neat polypropylene validate the potential of this proof-of-concept, closed-loop recyclable material. Future studies will investigate alternative, higher performance matrices.

Fabrication and Characterisation of Aligned Discontinuous Carbon Fibre Reinforced Thermoplastics as Feedstock Material for Fused Filament Fabrication

“…The use of fibres significantly beyond the critical length has in large part made up for deficiencies of the interface through the simple addition of interface area. In concurrent work, closed-loop recycling of thermoplastic matrix composites was investigated which showed an increase in strength over multiple recycling loops which shows an increase in strength may be possible by optimizing the fibre-matrix interface [ 16 , 17 ].…”

“…It was chosen to use 3 mm carbon fibres to ensure the critical length was exceeded. Toho Tenax C124 fibres were used which have been used with the HiPerDiF fibre alignment method before [ 15 , 17 , 63 , 64 ]. These fibres have a water-soluble sizing which allows them to disperse well in water which aids the HiPerDiF fibre alignment process.…”

“…Careful selection of the fibre length and matrix system allows for retention of most of the mechanical performance of a continuous fibre solution, without the need for cumbersome and restrictive fibre cutting and initial laydown procedures within the additive manufacturing process. This process may also be suitable for recycling of continuous fibre waste and enable a low-cost method for composite manufacture where rapid prototyping and a high degree of automation are required [ 16 , 17 ].…”

Hybrid composites of aligned discontinuous carbon fibers and self-reinforced polypropylene under tensile loading

“…This new method fabricates highly aligned discontinuous preforms directly from discontinuous fibers by suspending the discontinuous fibers in water and spraying the fiber suspension between several parallel plates. This technique is suited for production of polymer composites from recycled fibers [9][10][11][12], and is also applicable for mixing different fiber types [13] as well as fiber lengths [14].…”

Thermal aging influence on the damage mechanisms of fully recycled composite‐reinforced polypropylene/polyethylene blend

“…However, although the environmental conditions influence, mainly oxidation in the case of PP‐based composites, on the mechanical and physical properties have been investigated for many years and well understood , few studies were realized on the thermal aging influence on the local damage mechanisms of CFs‐reinforced polymer. Some of previous papers dealing with oxidation effect on in situ damage investigation have shown that the generation of micro‐cracks creates paths for oxygen to penetrate through the fiber–matrix interface. Thus the interface is oxidized and the material lifetime is consequently reduced.…”