Additive manufacturing of carbon fibre reinforced polyphenylene sulphide composites

Abstract

The emergence of high-performance carbon fibre reinforced thermoplastic (CFRTP) manufactured through material extrusion-based additive manufacturing (AM) techniques has gained special attention for its geometric flexibility, cost-effectiveness, and elimination of multiple processing tools. This thesis investigates the material extrusion-based AM of carbon fibre reinforced polyphenylene sulphide (CF/PPS) composites, focusing on thermal process conditions, fibre-matrix adhesion, interlaminar properties and sustainable printing, to produce high-performance CF/PPS composite parts suitable for high-end applications.

Initially, this study examines the thermal behaviour of discontinuously reinforced CF/PPS, manufactured additively through material extrusion. It centres on how thermal process conditions affect the degree of crystallinity, oxidation crosslinking, and mechanical properties of CF/PPS from filament fabrication and material extrusion to annealing treatment. Adjusting thermal treatment conditions allows for the design, control, and tailoring of crystallinity and mechanical properties in the printed CF/PPS composites.

Secondly, the study introduces an innovative one-step bio-inspired method, employing the copolymerisation of dopamine to graft silica nanoparticles onto carbon fibre surfaces. Extensive experimentation was conducted to fabricate these modified fibres and characterise the treated samples, assessing surface morphology and functional groups. The findings indicate that the polydopamine/silica nanoparticle (PDA/NPs) network significantly enhances interlaminar shear strength by 28.4% in the resultant composites. Additionally, dynamic mechanical analysis confirms robust interfacial bonding at the fibre-matrix interface, exhibiting impressive thermal cycling resistance.

Furthermore, this study explores the combined effects of pre-processing continuous carbon fibre (CCF) treatment with PDA/NPs network and post-processing printed parts with hot press compaction on the intralaminar attributes of 3D printed CCF/PPS. Results reveal marked improvements in interlaminar properties, with flexural strength and interlaminar shear strength (ILSS) increasing by 27% and 172%, respectively, compared to untreated samples. Molecular dynamics (MD) simulations and nano-indentation tests elucidate the mechanisms underlying the enhanced interfacial adhesion, attributed from PDA/NPs network on CCF. Differential scanning calorimetry (DSC) and microscopic analysis are employed to evaluate improvements in crystallinity and void content following post-processing. Additionally, this study introduces an innovative post-processing technique that utilises a salt bath, which is particularly advantageous for complex structures.

Lastly, this study establishes a basis for a sustainable in-situ remanufacturing system, integrating with 3D overprinting techniques. It examines the mechanical properties of reclaimed carbon fibre from commercial thermosetting composites and reshaped carbon fibre from printed thermoplastic composites, both with and without surface treatment. Moreover, reshaped short carbon fibre reinforced PPS composites, exhibiting enhanced performance, were repurposed in an in-situ repair process alongside original continuous carbon fibre filaments. The efficacy of in-situ bonding patches was tested on damaged open-hole PA6 laminates through tensile tests, with real-time failure analysis conducted using digital image correlation (DIC).

Overall, this thesis provides a comprehensive exploration into the additively manufactured CF/PPS composites, addressing critical aspects such as low degree of crystallinity of PPS polymer during the printing process, weak interfacial adhesion between carbon fibre and polymer matrix and poor interlaminar properties of printed CCF/PPS laminates. These approaches demonstrate significant improvements in mechanical properties and structural integrity, fulfilling the potential of additive manufacturing in producing high-quality, sustainable composites for engineering applications.