Additive manufacturing (AM), popularly called 3D printing, is driving a significant shift in manufacturing technology across a diverse range of industries, including innovative medical and engineering technologies.
Polymer-based material extrusion is one AM approach that stands out due to its affordability, versatility, and simplicity in the printing process.
Crystallisation plays a pivotal role in determining the mechanical and functional properties of the final product, yet the dynamic crystallisation behaviour during material deposition remains insufficiently explored.
To investigate how different processing conditions influence and dominate polymer crystallisation during AM, researchers from the University of Manchester (UK), the University of Bristol (UK), and Nanyang Technological University (Singapore) developed a novel X-ray diffraction (XRD) experimental configuration at Diamond’s B16 Test Beamline. Together with thermal modelling, they were able to dynamically monitor and control the crystallisation process in situ.
The paper, In situ X-ray diffraction and thermal simulation of material extrusion additive manufacturing of polymer, published in Materials & Design, offers real-time insights into how AM processing conditions impact nucleation, crystal growth, and the resulting microstructures of crystalline polymers – insights that are fundamental for designing and optimising the polymer AM process.
The findings demonstrate the potential parameter optimisation approaches that can lead to smaller, uniform crystals and enhanced mechanical properties and functionality, paving the way for advanced AM bio-medical and engineering applications where material consistency and performance are paramount.
Polymers encompass a wide range of materials, beyond familiar plastics. These range from specialised polymers designed for use in living organisms (polymer-based biomaterials), to composite materials created by combining polymers with other substances to achieve enhanced properties.
A critical knowledge gap during polymer-based material extrusion AM, however, is understanding the real-time crystallisation process, which is key to the tailoring of crystalline structures and the direction-dependent functions of crystal properties (crystalline anisotropy) for the processing of polymer-based materials.
Wajira Mirihanage from the University of Manchester explains how Diamond’s B16 Test Beamline provided the essential requirements for their experiments to probe the crystallisation process:
Most existing studies focus on static conditions, failing to capture the real-time evolution of crystallisation during the AM process. In contrast, we were able to perform real-time observation of crystallisation during the complicated AM process. In situ time resolved synchrotron X-ray diffraction was made possible by exploiting the advantages of instrumentation, flexibility and specialised support available at Diamond Light Source’s B16 Test Beamline. The experimental results were paired with advanced thermal simulations to analyse the evolution of temperature and crystallisation with time.
B16’s advanced instrumentation and experienced technical support established the critical experimental conditions required. These included the correct X-ray beam characteristics, such as energy, photon flux, beam size, suitable detectors and their configuration.
Oliver Fox, beamline scientist at B16, describes how the beamline’s flexibility was also key to the success of this work:
The challenge for us on B16 was to make sure the 3D printer setup fitted onto the beamline, without blocking the diffracted beam from the sample. At B16 we're versatile in what we can build, and we work closely with users to put together experiments with a bespoke setup. For this study, we were able to modify the sample end station to accommodate the 3D printer assembly on the beamline and collect the diffraction data as the printer was operated. That's not possible at most beamlines.”
The experiments involved extruding the polymer from a printer nozzle onto a substrate and observing the diffraction of the X-rays emitted through the polymer as it cooled. In situ XRD measurements were designed to continuously monitor a specific volume of the material throughout the cooling process, providing crucial insights into the polymer’s structural evolution as the polymer transitioned from the molten to the solid state.
A numerical model was employed to simulate the thermal behaviour, supporting the interpretation of experimental observations. Nucleation and crystallisation potential with reference to key processing parameters (temperature and speed) were analysed.
The results confirmed that printing temperature was the dominant factor influencing crystallisation. Optimal combinations of temperature-related parameters were identified to significantly enhance the formation of desirable crystal structures, revealing how marginally low processing temperatures can accelerate the nucleation and crystallisation. Additionally, the benefit of the relatively slower deposition velocities for higher crystallinity was demonstrated.
Unlike prior studies, the research focuses on a holistic understanding of process-structure-property relationships to enable precise control over the AM process, including optimising AM processes for improved and microstructural uniformity, mechanical and functional properties in 3D printed bio-constructs and carbon nanomaterials.
One example is the fabrication of multi-material functional gradient bone tissue engineering scaffolds in the treatments of critical-sized bone defects, osteochondral defects, and spinal fusion surgeries, amongst others. Here material anisotropy is utilised to guide how new bone tissue forms (osteogenesis).
Wajira explains the benefits of their new insights for bio-medical implants:
The enhanced understanding we have gained brings us closer to using polymer-based bio-materials implants instead of current metallic bio implants. In specific cases, metallic implants develop issues like stress shielding and the requirement for second surgeries. Enhancement of the properties of polymer-based bio-implants can make it possible to overcome such issues.
In aerospace engineering, advanced AM has made rapid fabrication and development of light-weight carbon nanomaterial-reinforced blades possible for drone applications. The insights gained here will enable the additive manufacturing of components with even better mechanical properties in the future. These enhanced properties will contribute to improved drone performance, resilience, and survivability, which are crucial for operations in extreme conditions.
Going forward, the research described in the paper is continuing with a new PhD project and an extension of the research is planned. Commercial 3D printer developers have been engaged by the research collaboration to customise the printer configurations based on the scientific understanding obtained.
With their experimental knowledge, the research collaboration is currently pursuing further studies which will enhance the design and fabrication of crucial biomedical implants.
One such study is the numerical simulation of the phenomena to predict the thermal behaviour of additively manufactured bone tissue scaffolds made from biodegradable polymers [1]. Another field is advanced 3D-printer development for tissue engineering scaffolds and 3D structures that support cell attachment, proliferation, and differentiation [2].
To find out more about the B16 beamline, please contact the Principal Beamline Scientist: Kawal Sawhney: [email protected]
Weiguang Wang, Yanhao Hou, Jiong Yang, Zhengyu Yan, Fengyuan Liu, Cian Vyas, Wajira Mirihanage, Paulo Bartolo, In situ X-ray diffraction and thermal simulation of material extrusion additive manufacturing of polymer, Materials & Design, Volume 245, 2024, 113255, ISSN 0264-1275, https://doi.org/10.1016/j.matdes.2024.113255.
[1] Yang, J.; Yue, H.; Mirihanage, W.; Bartolo, P. Multi-Stage Thermal Modelling of Extrusion-Based Polymer Additive Manufacturing. Polymers 2023, 15, 838. https://doi.org/10.3390/polym15040838
[2] Yang, J., Mirihanage, W., Bartolo, P. (2023). Novel Extrusion Based Co-axial Printing Head for Tissue Engineering. In: Correia Vasco, J.O., et al. Progress in Digital and Physical Manufacturing. ProDPM 2021. Springer Tracts in Additive Manufacturing. Springer, Cham. https://doi.org/10.1007/978-3-031-33890-8_6
image credits: figure 1: Diamond Light Source; figure 2: 10.1016/j.matdes.2024.113255 under CC BY 4.0 licensing
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