Above: Virginia Tech 3D Printed latex impeller at 100 micron resolution/Image Credit: Virginia Tech
An interdisciplinary group of chemistry and mechanical engineering researchers from Virginia Tech have developed a novel process to 3D Print Latex Rubber, thereby unlocking the ability to print a variety of elastic materials with complex geometric shapes.
Latex a group of polymers — long, repeating chains of molecules — coiled inside nanoparticles dispersed in water. It basically is a soft rubber typically constituting fifty-five percent water and around forty percent rubber material. It is most commonly used in products like gloves, swim caps, mattresses, balloons, etc.
With the new process giving ability to 3D print latex rubber, researches feel that a variety of applications including soft robotics, medical devices, or shock absorbers can now be effectively produced.
3D PRINT LATEX RUBBER
While efforts have been made to 3D print latex rubber in the past but due to some long-standing limitations of 3D printing it never crossed the research stage. But the Virginia Tech researchers have chemically modified liquid latexes to make them printable and built a custom 3D printer with an embedded computer vision system to print accurate, high-resolution features of this high-performance elastic material.
Speaking about the novel process, Timothy Long, a professor of chemistry and a co-principal investigator on this project along with Christopher Williams, the L.S. Randolph Professor of mechanical engineering and interim director of MII said, “This project represents the quintessential example of interdisciplinary research. Neither of our labs would be able to accomplish this without the other.”
This project is a joint collaboration between Virginia Tech and Michelin North America via a National Science Foundation award aligned with the Grant Opportunities for Academic Liaison with Industry program, which supports teamed research between academia and industry. Details of their initial results are detailed in a journal article published in ACS Applied Materials & Interfaces.
NOVEL MATERIALS DEVELOPMENT IN SCIENCE
Above: Virginia Tech chemists and mechanical engineers from the research groups of Timothy Long and Christopher Williams collaborated on this project/Image Credit: Virginia Tech
After unsuccessful attempts to synthesize an elastic material that would provide the ideal molecular weight and mechanical properties, Phil Scott, a fifth-year macromolecular science and engineering student in the Long Research Group, turned to commercial liquid latexes.
The researchers ultimately wanted this elastic material in a solid 3D printed form, but Scott first needed to augment the chemical composition to allow it to print.
Scott ran into a fundamental challenge: liquid latex is extremely fragile and difficult for chemists to alter.
According to Viswanath Meenakshisundaram, a fifth-year mechanical engineering Ph.D. student in the Design, Research, and Education for Additive Manufacturing Systems Lab who collaborated with Scott. “Latexes are in a state of zen. If you add anything to it, it’ll completely lose its stability and crash out.”
Then, the chemists came up with a new idea of building a scaffold, similar to those used in building construction, around the latex particles to hold them in place. This way, the latex could maintain its great structure, and Scott could add photoinitiators and other compounds to the latex to enable 3D printing with ultraviolet (UV) light.
Scott added, “When designing the scaffold, the biggest thing you have to worry about is stability of everything. 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 really fun challenge.”
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NOVEL PROCESSING DEVELOPMENT IN ENGINEERING
Above: A Vat Photopolymerization 3D printer/Image Credit: Zortrax
While Scott tinkered with the liquid latex, Meenakshisundaram had to figure out how to correctly print the resin. The researchers chose to use a process called vat photopolymerization, in which the printer uses UV light to cure, or harden, a viscous resin into a specific shape.
Needing a printer capable of printing high-resolution features across a large area, Meenakshisundaram built a new printer. He and Williams, his advisor, came up with the idea to scan the UV light across a large area, and in 2017, they filed a patent for the printer.
Even with the custom printer, the fluid latex particles caused scattering outside of the projected UV light on the latex resin surface, which resulted in printing inaccurate parts, so Meenakshisundaram devised a second novel idea. He embedded a camera onto the printer to capture an image of each vat of latex resin. With his custom algorithm, the machine is able to “see” the UV light’s interaction on the resin surface and then automatically adjust the printing parameters to correct for the resin scattering to cure just the intended shape.
Williams explained, “The large-area scanning printer was a concept I had, and Viswanath made it into reality in short order. Then Viswanath came up with the idea of embedding a camera, observing how the light interacts with the elastic material, and updating the printing parameters based on his code. That’s what we want from our Ph.D. students: We provide a vision, and they accomplish that and grow beyond as an independent researcher.”
Meenakshisundaram and Scott discovered their 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.
Meenakshisundaram said, “An interpenetrating polymer network is like catching fish in a net. The scaffold gives it a shape. Once you put that in the oven, the water will evaporate, and the tightly coiled polymer chains can relax, spread or flow, and interpenetrate into the net.”
The two professors have made it possible to 3D print latex rubber and this provides a conceptual framework for printing a range of unprecedented materials from rigid plastics to soft rubbers, which have been unprintable until now.
“When I was a graduate student working on this technology, we were excited to get unique performance from the shapes we could create, but the underlying assumption was we had to make do with very poor materials,” Williams said. “What’s been so exciting about this discovery with Tim’s group is being able to push the boundary of what we assumed was the limit of a printed material’s performance.”
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