Virginia Tech researchers have discovered a novel process for 3D printing latex rubber that opens up the possibility of printing a variety of elastic materials with complex geometric shapes.
Latex, commonly known as glove or paint material, refers to a group of polymers – long, repeating chains of molecules – that are wrapped in nanoparticles dispersed in water. 3-D printed latex and other similar rubber-like materials called elastomers could be used for a variety of applications, including soft robotics, medical devices, or shock absorbers.
3-D printed latex has been documented only a few times in the scientific literature. None of the previous examples comes close to the mechanical properties of latex printed by an interdisciplinary team affiliated with the Macromolecules Innovation Institute (MII), the College of Science and the College of Engineering.
Thanks to new innovations in both chemistry and mechanical engineering, the team overcame some long-term limitations of 3D printing, also known as additive manufacturing. The researchers chemically modified liquid latices 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 material.
“This project is the epitome of interdisciplinary research,” said Timothy Long, professor of chemistry and co-principal investigator on the project, along with Christopher Williams, LS Randolph professor of mechanical engineering and interim director of MII. “Neither of our laboratories would be able to do this without the other.”
This project is a collaboration between Virginia Tech and Michelin North America through a National Science Foundation award that is in line with the Grant Opportunities for Academic Liaison with Industry program, which supports collaborative research between science and industry. Details of their first results are given in a magazine article published in ACS Applied Materials & Interfaces.
Novel material development in science
After unsuccessful attempts to synthesize a material that offers the ideal molecular weight and mechanical properties, Phil Scott, a fifth-year student of macromolecular science and technology in the Long Research Group, turned to commercial liquid latices.
The researchers ultimately wanted this material in a solid 3D printing form, but Scott first had to increase the chemical composition so that it could be printed.
Scott faced a fundamental challenge: liquid latex is extremely fragile and difficult for chemists to change.
“Latexes are in a zen state,” said Viswanath Meenakshisundaram, a fifth-year graduate student in mechanical engineering. Student in design, research, and training for additive manufacturing systems who worked with Scott. “If you add something, it completely loses its stability and crashes.”
Then the chemists came up with a new idea: what if Scott built a scaffold similar to that used in building construction around the latex particles to hold them in place? In 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.
“When designing the scaffold, the main thing to worry about is the stability of everything,” said Scott. “It took a lot of reading to learn even basic things like why colloids are stable and how colloidal stability works, but it was a really fun challenge.”
Novel processing development in engineering
While Scott was working on the liquid latex, Meenakshisundaram had to figure out how to print the resin properly. The researchers opted for a process called vat photopolymerization, in which the printer uses UV light to cure or cure a viscous resin into a specific shape.
Meenakshisundaram needed a printer that could print high-resolution functions over a wide area and built a new printer. He and Williams, his advisor, came up with the idea of scanning the UV light over a large area and filed a patent for the printer in 2017.
Even with the custom printer, the liquid latex particles caused scatter outside of the projected UV light on the latex resin surface, causing inaccurate parts to be printed. So Meenakshisundaram developed a second novel idea. He embedded a camera in the printer to take a picture of each tub of latex resin. With its custom algorithm, the device can “see” the interaction of UV light on the resin surface and then automatically adjust the printing parameters to correct the resin scatter and only cure the intended shape.
“The large-scale scan printer was a concept I had, and Viswanath quickly turned it into a reality,” said Williams. “Then Viswanath came up with the idea of embedding a camera, observing how the light interacts with the material, and updating the printing parameters based on his code. This is what we want from our doctoral students: We offer a vision and you achieve it and grow as an independent researcher. “
Meenakshisundaram and Scott discovered that their final 3D printed latex parts showed strong mechanical properties in a matrix known as a semi-interpenetrating polymer network, which had not been documented in the previous literature on elastomeric latices.
“A penetrating polymer network is like catching fish in a network,” said Meenakshisundaram. “The scaffold gives it a shape. As soon as you put it in the oven, the water evaporates and the tightly wrapped polymer chains can relax, spread or flow and penetrate the net.”
An approach to making molecules
The new advances in both material development and material processing underline the interdisciplinary environment between the two groups.
Long and Williams both recognized their peers’ expertise to enable the collective breakthrough.
“My philosophy is that this kind of innovation can only be achieved if you work with people who are very different from you,” said Long.
The two professors said 3-D printed latex provides the conceptual framework for printing a range of unprecedented materials, from rigid plastics to soft rubbers that were previously unprintable.
“When I was a PhD student working on this technology, we were excited to get a unique performance out of the shapes we could create, but the underlying assumption was that we had to make do with very poor materials,” said Williams . “What was so exciting about this discovery with Tim’s group is the ability to push the boundaries of what we thought was the limit of a substrate’s performance.”
Stretchable foam for 3D printing of large objects
Philip J. Scott et al. 3D printing latex: a path to complex geometries of high molecular weight polymers, ACS Applied Materials & Interfaces (2020). DOI: 10.1021 / acsami.9b19986
Provided by Virginia Tech
Quote: Researchers report the breakthrough of 3D-printed latex rubber (2020, July 15), which was retrieved on July 15, 2020 from https://phys.org/news/2020-07-d-latex-rubber-breakthrough.html has been
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