3D printing of virgin and recycled thermoplastic materials: fabrication, testing, characterisation and optimisation

Abstract

Additive manufacturing (AM) is a revolutionary technique that permits the fabrication of 3D objects with complex 3D shapes but at a low cost, light weight, and with less waste. Among other common techniques, the fused filament fabrication (FFF) technique is currently dominating the industry with its ability to not only customise products and produce objectives with intricate profiles but also adopt recycled materials for a more sustainable process. To guarantee reliable printings and high-quality products, understanding the influence of process parameters, building predictive models, and performing multi-objective optimisations are highly recommended. As the current studies show product’s quality is strongly influenced by polymers’ degradation for FFF, more studies should explore the use of fused granulate fabrication (FGF) which also belongs to the material extrusion family but skips one thermo- mechanical stage, expecting to reduce the effect of degradation.

With the assistance of statistical models, mathematical models, and numerical modelling methods, this 3-year research aims to optimise the 3D printing process by setting key parameters and the properties of FFF and FGF-printed parts using virgin, recycled thermoplastic materials and their composites. The thesis is organised in two parts: Part I (Chapters 3 to 5) investigates the process-property relationships in FFF, while Part II (Chapters 6 to 9) extends these findings to FGF for large-scale applications.

The outcomes of this research provide a robust foundation for advancing industrial applications and design for AM involving recycled thermoplastic materials. By enabling accurate, multiscale prediction of mechanical properties and process optimisation, the developed frameworks empower designers and engineers to efficiently tailor process parameters, reducing costly experimental iterations and accelerating product development. Integrating advanced damage and failure models will further enhance reliability, while refined mesoscale analyses of interlayer bonding will deepen understanding of structural behaviour. Expanding these tools to encompass diverse recycled polymers, composites, and additive reinforcements such as natural fibres or carbon-based fillers will support the creation of sustainable, high-performance materials tailored to specific industrial needs. Collectively, these advances promote more sustainable manufacturing practices, facilitate wider adoption of recycled materials in AM, and help designers meet stringent performance requirements across automotive, medical, consumer, and other sectors.

Date of Thesis submission	2026
Original language	English
Awarding Institution	Western Sydney University
Sponsors	Australian Government Research Training Program Scholarship
Supervisor	Richard Yang (Supervisor), Sarah Zhang (Supervisor), Leo Zhang (Supervisor) & Tosin Famakinwa (Supervisor)