Optimisation of design and manufacturing process for fused deposition modelling of reclaimed carbon fibre reinforced polyamide-6 composites

Abstract

Nowadays, the most pressing issues concerning environmental protection and waste management for composites are the reclamation of thermoplastics, recycling of reclaimed carbon fibre (rCF) from composite wastes associated with fibre re-manufacturing into rCF-reinforced thermoplastic composites (rCFRPs). However, rCFRPs recycling via Fused Deposition Modelling (FDM) has been insufficiently studied. The existing studies have shown that their related products have exhibited relatively low mechanical properties. Thus, the underperforming FDM-printed rCFRPs did not meet their theoretical mechanical potential as expected, hindering industrial applications.
This work has demonstrated the re-manufacturing feasibility and optimisation of mechanical properties for rCFRPs via FDM recycling. The raw materials utilised in this work were rCFs recovered by pyrolysis from composite scraps and two types of thermoplastics, including virgin polyamide-6 (PA), and reclaimed PA (rPA) derived from end-of-life fishnet by mechanical recovery. In Chapter 3, the feasibility of rCFRPs recycling via FDM has been determined. The process optimation of eight process parameters, involving layer thickness (LH), raster angle (RA), air gap (AG), printing speed (PS), liquefier temperature (Ptemp.), envelope temperature (Etemp.), cooling and fibre content, was conducted by a fractional factorial design (FrF-design) for primary parameter screening. Immediately followed by Chapter 4, the crucial process parameters have been optimised by a centre composite circumscribe (CCC) method to develop the full mechanical properties of rCFRPs.
The key conclusions of this work are summarized as follows:
(1). LH, RA, AG and fibre content were four crucial parameters during the rCFRPs recycling via FDM.
(2). These four parameters significantly affected the thermal and mechanical properties of rCFRPs, associated with morphologies involving fibre length, orientation, aggregation, voids and fracture surface. The LH, RA and AG had the most influence on the mechanical properties of rCFRPs. While the effect of fibre content on fibre length, orientation, aggregation, voids and fracture surface of rCFRPs was more pronounced than the others. In particular, it has been found that rCFRPs with 40 wt.% fibre mass fractions showed relatively poor tensile and flexural properties. This is attributed to poor fibre orientation and high porosity (>20 %) of rCFRPs, induced by fountain flow effects due to high fibre content.
(3). The full mechanical potential of rCFRPs during the FDM recycling has been developed at optimal process parameters occurring at 0.1 mm LH, 0 ° RA, -0.03 mm AG and 20 wt.% fibre content of rCFs. The optimised flexural strength and modulus of FDM-printed rCFRPs were up to 167 MPa and 9.14 GPa, respectively, whilst in tension, the strength and modulus were up to 150 MPa and 8.03 GPa. These mechanical properties were up to 341 % higher than the unreinforced polyamide and comparable to those of FDM-printed commercial composites with 20 wt.% virgin CFs, which indicated promising prospects in industrial applications.

Date of Award	15 Mar 2023
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Xiaoling Liu (Supervisor), Robert Pierce (Supervisor) & Chris Rudd (Supervisor)