Wu, Yuyang
(2023)
Investigation of processing polyurethane via reactive extrusion 3D printing.
PhD thesis, University of Nottingham.
Abstract
Additive manufacturing (AM, also known as 3D Printing) describes a range of technologies that build structures layer by layer to translate a 3D computer aided design parts into functional solid objects for different customised applications. Polyurethane (PU) is a polymer with versatile applications used as foams, coatings, adhesives, and biomedical devices, due to the easily tuneable rubbery/rigid nature. To push a broader industrial application of AM functional polymeric parts, such as polyurethane (PU), research in the academia field explored the
desirable PU functionalities through a range of AM technologies.
Reactive Extrusion 3D Printing (REX) is one of the AM technologies pursued to realise the potential of AM PU functional parts. REX is a newly invented manufacturing route1, whereby two feeds comprising reactive functional groups are mixed in-situ during the process and
extruded to construct 3D structures. At its early stage, the few research conducted in the REX field focused on demonstrating the capability of printing isotropic and functional graded parts through in-situ tailoring of the reaction and targeted on fabricating large-scale structure with fast deposition speed.
There is a clear gap in the AM PU via REX, to systematically understand the processing of PU via REX process. Therefore, this PhD project started by establishing a workflow: progressing from screening the printability of PU feedstocks through a printing optimisation for these feedstocks, to achieve good resolution / reproducibility by investigating the filament quality produced. It highlighted that transitional ink rheology as the key characterisation tools for the formulation printability analysis, and optimum flowrate to be the key parameter to evaluate during process optimisation.
In REX, the mixing efficiency and reaction kinetics are highly synergistic. Furthermore, both are greatly influenced by the rheology of the two feeds. the effects of which are relatively unexplored. To understand the impact of feed rheology on the print quality, three mixing modes
differed by distinct rheological properties of the isocyanates and polyol dual feeds were designed and investigated by leveraging PU reaction. This was achieved through incorporating different amount of fumed silica into feeds as rheology modifier. It demonstrated the properties
of 3D printed PU can be tuneable by adjusting the rheological relationship between the isocyanates and polyol feeds. Both viscosity ratio and elasticity ratio of the feeds influenced the mixing efficiency, the reaction kinetics, and the quality of the printed structures. The
isocyanates and polyol feeds demonstrating great differences in viscosity and elasticity reacted more rapidly due to less restriction in diffusion of feed materials during mixing. Consequently, a high level of cross-linking was achieved within the printed PU structure, resulting in better
thermal properties and improved stiffness than the other two mixing modes investigated. It showed feed rheology shall be optimised to find the best combination of MMs, with prominent printing performance.
To further explore the effect of filler on the process and enhance the cross-linking network of such PU systems, two types of functional silica nanoparticles (FSP) were developed (SiO2-NH2 and SiO2-NH2/CH3) and served as reactive filler to afford hybrid reinforcing effect in the matrix
through physical entanglements and intramolecular bonding. This study has successfully demonstrated such dual-network reinforcing effect with SiO2-NH2/CH3 reinforced PU system,
showed faster reaction kinetics, higher glass transition temperature, better thermal stability,and enhanced increments in storage modulus than the SiO2-NH2 reinforced system. Furthermore, SiO2-NH2/CH3 reinforced PU system exhibited comparable thermo-mechanical properties, with commercial fumed silica particles (SiO2-PDMS) filled PU system. The improvement in FSP reinforcing efficiency was attained by improving the dispersion of SiO2-NH2/CH3 in matrix and the formation of additional urea bonds in the structure. Without the alkyl groups on the particle surface, SiO2-NH2 reinforced PU composite exhibited significantly inferior printing performance, as the results of SiO2-NH2 aggregation. It hindered the widelyformation of PU reaction and further inhibited the cross-linking networks.
These findings offer guidance on further developing reactive formulations in material extrusion AM, enabling a greater variety of chemistries with tuneable functions to be 3D printed in the future. It also offers guidance on developing FSPs with additional functionality and 3D printing
of multi-functional nanoparticle reinforced composite systems. It has shown that the concept of introducing dual-network particle reinforcing filler to strengthen the REX matrix materials, opens a new route for developing advanced nanoparticle reinforcement composite systems via AM.
| Item Type: |
Thesis (University of Nottingham only)
(PhD)
|
| Supervisors: |
Derek, Irvine
Ricky, Wildman
Christopher, Tuck
Zhou, Zuoxin |
| Keywords: |
Additive manufacturing; Polyurethane; Reactive extrusion 3D printing; Material extrusion |
| Subjects: |
T Technology > TS Manufactures |
| Faculties/Schools: |
UK Campuses > Faculty of Engineering > Department of Mechanical, Materials and Manufacturing Engineering |
| Item ID: |
72371 |
| Depositing User: |
Wu, Yuyang
|
| Date Deposited: |
12 Nov 2025 09:25 |
| Last Modified: |
12 Nov 2025 09:25 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/72371 |
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