Integration of Auxetic Structures Through 3D Printing and Hot Embossing into Polyethylene Fabrics for Aerospace Applications

Additive manufacturing (AM) significantly enhances material design and functionality. Our research leverages advanced AM techniques, specifically knitting of melt-spun polymer fibers, electrospinning, and the combination of 3D printing and hot embossing, to develop innovative polyethylene (PE)-based composite materials primarily for aerospace applications to provide passive thermoregulation, radiation shielding, and auxetic capabilities.<br/>The core technologies employed in our additive manufacturing processes include knitting, electropinning, FDM 3D printing, and hot embossing. Knitting involves interloping yarns to create flexible and elastic fabrics, while electrospinning produces ultra-fine fibers from polymer solutions, forming non-woven fabrics with a high surface area-to-mass ratio [1]. Hot embossing is used to imprint patterns onto material surfaces, enhancing their mechanical properties such as indentation resistance and energy absorption, relevant in protective gear applications [2]. Lastly, FDM 3D printing builds objects layer by layer from digital models, allowing for the creation of complex geometries [3]. Both 3D printing and hot embossing can produce auxetic structures (materials that thicken perpendicular to applied force) offering significant advantages to develop materials with high impact resistance and mechanical integrity [4]. While 3D printing serves as a quick prototyping tool, hot embossing may act as a bridge to high-volume production of such prototypes.<br/>For aerospace applications, polyethylene's (PE) high hydrogen content makes it one of the best materials for radiation shielding while being durable, recyclable, and chemically resistant [5]. Also, the addition of fillers can improve shielding against high-penetration sources such as neutrons. Conveniently, the addition of fillers is straightforward in FDM printing, electrospinning, and polymer extrusion for yarn making. Therefore, it is possible to integrate knitted fabrics with high elasticity and flexibility, electrospun fibers with a high surface area-to-mass ratio, versatility in composition, and lightweight, and auxetic structures with enhanced mechanical properties and highly customizable architectures. Our integrated AM approach significantly enhances the effectiveness of radiation shields in aerospace applications. The lightweight nature of the designed materials contributes to lower launch costs and increased payload efficiency, while their enhanced protective properties ensure greater safety for spacecraft and satellites. The applications of the developed techniques are not limited to aerospace; with the proper selection of materials and architectures, they can potentially be extended to the automotive industry and healthcare, due to their versatility.<br/>This work has been supported by the ONR-Global Award N62909-23-1-2109, Tec-MIT collaborative research program in Nanotechnology, Partially funded by the Challenge Research Funding Program of Tecnologico de Monterrey, and the MIT MechE MathWorks fellowship to Duo Xu. We acknowledge also the MIT UROP office for supporting Kenneth Oranga.<br/><b>References</b><br/>[1] X. X. He <i>et al.</i>, Near-Field Electrospinning: Progress and Applications, <i>Journal of Physical Chemistry C</i>, 121(16), 8663–8678, 2017.<br/>[2] Y. J. Lu <i>et al.</i>, Co-printing of micro/nanostructures integrated with preconcentration to enhance protein detection, <i>Microfluid Nanofluidics</i>, 28(1), 1–10, 2024.<br/>[3] S. F. Iftekar, et al, Advancements and Limitations in 3D Printing Materials and Technologies: A Critical Review, <i>Polymers (Basel)</i>, 15(11), 2023.<br/>[4] M. Mir, et al, Review of mechanics and applications of auxetic structures, <i>Advances in Materials Science and Engineering</i>, 2014, 1–17, 2014.<br/>[5] L. Narici <i>et al.</i>, Performances of Kevlar and Polyethylene as radiation shielding on-board the International Space Station in high latitude radiation environment, <i>Sci Rep</i>, 7(1), 1–11, 2017.