Researchers at Virginia Tech have found a way to 3D print latex rubber! As a result, this allows the ability to print a variety of elastic materials with complex geometric shapes.
Latex
Commonly known as the material used in gloves and paint, it refers to a group of polymers. These are long, repeating chains of molecules. These are coiled inside nanoparticles which are dispersed in water. We could use 3D printed latex rubber and alike rubbery materials for many different applications. These include medical use, shock absorbers, and even soft robotics.
3D printed latex rubber has only been written about a few times in scientific literature. No previous examples come close to the properties of the latex printed by an interdisciplinary team involved with the MII (Macromolecules Innovation Institute), the College of Science, and the College of Engineering. With innovations in both the chemistry and mechanical engineering disciplines, the team overcame the limitations of 3D printing. Researchers chemically changed liquid latexes to make them printable, and they developed a custom 3D printer to print accurate, high-resolution features of this high-performance material.
Developing Science
After failed attempts to manufacture a material that would provide the correct weight and mechanical properties, Phil Scott, a 5th year macromolecular science and engineering student in the Long Research Group, looked into commercial liquid latexes. Researchers wanted this material in a solid 3D printed form, but Phil Scott first needed to develop the chemical composition in order for it to print. Unfortunately, they ran into a fundamental challenge: liquid latex is fragile and difficult for chemists to change. The chemists came up with a fresh idea: What if a scaffold we built? Similar to those used in building construction, around the latex particles to hold them in place? This way, the latex could maintain its impressive structure and other compounds can be added to the latex to enable 3D printing with UV light!
“When designing the scaffold, the biggest thing you have to worry about is stability of everything,” Scott said. “It took a lot of reading, even stuff as basic as learning why colloids are stable and how colloidal stability works, but it was a fun challenge.”
Engineering Development
Whilst the liquid latex rubber was investigated, it needed a way to figure out how to print the resin. The researchers used a process called vat photopolymerization. This is when the printer uses UV light to cure liquid resin into the desired shape.
Needing a printer capable of printing high-resolution features across a sizeable area, it built a new 3D printer. They came up with the idea to scan the UV light across a sizeable area. In 2017, they filed a patent for the printer.
Even with this fresh printer, the fluid latex caused scattering outside of the projected UV light on the latex resin surface. As a result, this caused inaccurate parts. A second idea was devised. They embedded a camera onto the printer to capture an image of each vat of latex resin. With a custom algorithm, the machine can “see” the UV light’s interaction on the resin surface. It then automatically adjusts the printing parameters to correct for the resin to cure as intended.
They soon discovered it that the final 3D printed latex parts exhibited strong mechanical properties in a matrix known as a semi-interpenetrating polymer network, which hadn’t been documented for elastomeric latexes in the prior literature.
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