The development of a lightweight material that is both strong and highly ductile has long been considered a desired goal in the field of structural materials, but these properties are usually mutually exclusive. However, researchers at the City University of Hong Kong (CityU) recently discovered a low-cost, direct method to transform commonly used 3D printing polymers into lightweight, ultra-strong, biocompatible hybrid carbon microlattices that can be any shape and size and are 100 times stronger than the original polymers . The research team believes that this innovative approach can be used to create complex three-dimensional parts with customized mechanical properties for a wide range of applications, including coronary stents and bio-implants.
Metamaterials are materials designed to have properties that natural materials do not have. Metamaterials with three-dimensional architectures, such as microlattices, combine the advantages of facile structural design principles with the intrinsic properties of their constituent materials. Creating these microlattices often requires advanced fabrication technologies such as additive manufacturing (commonly referred to as 3D printing), but the range of materials available for 3D printing is still quite limited.
“3D printing is becoming a ubiquitous technology for producing geometrically complex components with unique and customizable properties. Strong and durable architectural components typically require 3D printing from metals or alloys, but these are not readily available due to the high cost and low resolution of commercial metal 3D printers and raw materials Polymers are more available but usually not available mechanical strength or durability. We have found a way to transform these weaker and more fragile 3D-printed photopolymers into ultra-strong 3D architectures comparable to metals and alloys simply by heating them under the right conditions, which is amazing,” said Professor Lu Yang from the Department of Mechanical Engineering (MNE) and Department of Materials Science and Engineering (MSE) of CityU, who supervised the study.
A new method of increasing strength without compromising ductility
So far, the most effective approach to increase strength is through these 3D-printed materials polymer there are grates pyrolysis, a heat treatment that turns all polymers into ultra-durable carbon. However, this process strips the original polymer lattice of almost all of its ability to deform and creates an extremely fragile material such as glass. Other methods of increasing the strength of polymers also usually lead to deterioration of their ductility.
A team led by Professor Lu discovered a “magical” state in the pyrolysis of 3D-printed photopolymer microlattices, resulting in a 100-fold increase in strength and a doubling of the plasticity of the original material. Their results were published in a scientific journal Matter titled “Lightweight, Ultra-Strong Hybrid Carbon Microlattices with Three-Dimensional Architecture.”
They found that by carefully controlling the heating rate, temperature, duration, and gas environment, the stiffness, strength, and ductility of a 3D-printed polymer microlattice can be dramatically increased simultaneously in one step.
Through various characterization techniques, the team found that simultaneous improvements in strength and ductility are only possible when the polymer chains are “partially carbonized” by slow heating, where the polymer chains are incompletely converted to pyrolytic carbon, forming a hybrid material in which both polymer chains are loosely bound and carbon fragments coexist synergistically. The carbon fragments serve as reinforcements that strengthen the material, and the polymer chains limit the fracture of the composite.
The ratio of polymer to carbon fragments is also critical to obtain optimal strength and ductility. If there are too many carbon fragments, the material becomes brittle, and if there are too few, the material lacks strength. Through experiments, the team successfully created an optimally carbonized polymer lattice that was more than 100 times stronger and more than twice as ductile as the original polymer lattice.
Benefits other than improved mechanical properties
The research team also found that these “hybrid carbon” microlattices showed improved biocompatibility compared to the parent polymer. Through cytotoxicity and cell behavior monitoring experiments, they proved that cells cultured on hybrid carbon microarrays were more viable than cells seeded on polymer microarrays. The improved biocompatibility of hybrid carbon lattices means that the benefits of partial carbonization can extend beyond improved mechanical properties and potentially improve other functionalities.
“Our work provides a low-cost, simple and scalable route to create lightweight, strong and ductile mechanical metamaterials of virtually any geometry,” said Professor Lu. He suggests that the newly invented approach can be applied to other types of functional polymers, and that the geometrical flexibility of these architectural hybridscarbon metamaterials will enable them mechanical properties be adaptable to a wide range of applications such as biomedical implants, mechanically robust scaffolds for micro-robots, energy harvesting and storage devices.
Professor Lu is the corresponding author and Dr James Utama Surjadi, a postdoctoral fellow in his group, is the first author of the paper. Collaborators include Professor Wang Tsuankai, Professor of the Department of MNE, and Dr. Raymond Lam Hiuwai, Deputy Head and Associate Professor of CityU’s Department of Biomedical Engineering.
James Utama Surjadi et al. Lightweight, ultra-strong hybrid carbon microlattices with three-dimensional architecture, Matter (2022). DOI: 10.1016/j.matt.2022.08.010
City University of Hong Kong
Citation: Research team discovers how to transform 3D-printed polymer into stronger, more malleable hybrid carbon microlattice material (2022, September 7) Retrieved September 7, 2022, from https://phys.org/news/2022-09-team -3d-printed-polymer-stronger-ductile.html
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