Researchers report on the advancement of 3D printed latex rubber

Virginia Tech researchers have discovered a novel process for 3D printing latex rubber, unlocking the ability to print a variety of elastic materials with complex geometric shapes.

Latex, commonly known as the glove or paint material, refers to a group of polymers, long repeating chains of molecules, wound inside water-dispersed nanoparticles. 3D printed latex and other rubber-like materials called elastomers could be used for a variety of applications, including soft robotics, medical devices, or shock absorbers.

3D printed latex has been documented only a handful of times in the scientific literature. None of the above examples comes close to the mechanical properties of latex printed by an interdisciplinary team affiliated with the Macromolecules Innovation Institute (MII), the Faculty of Science, and the Faculty of Engineering.

Through breakthrough innovations in the disciplines of chemistry and mechanical engineering, the team overcame some long-standing limitations of 3D printing, also known as additive manufacturing. The researchers chemically modified the liquid latexes to make them printable, and built a custom 3D printer with an integrated computer vision system to print precise, high-resolution characteristics of this high-performance material.

“This project represents the quintessential example of interdisciplinary research,” said Timothy Long, professor of chemistry and co-principal investigator for this project, along with Christopher Williams, the LS Randolph professor of mechanical engineering and interim director of MII. “Neither of our labs could accomplish this without the other.”

This project is a joint collaboration between Virginia Tech and Michelin North America through a National Science Foundation award aligned with the Academic Liaison to Industry Grant Opportunities program, which supports joint research between academia and industry. Details of their initial results are detailed in a journal article published in Applied materials and ACS interfaces.

Development of new materials in science.

After unsuccessful attempts to synthesize a material that would provide the ideal molecular weight and mechanical properties, Phil Scott, a fifth-year student of macromolecular science and engineering at the Long Research Group, turned to commercial liquid latexes.

The researchers finally wanted this material in a solid 3-D printed form, but Scott first needed to increase the chemical composition to allow it to print.

Scott was faced with a fundamental challenge: Liquid latex is extremely brittle and difficult for chemists to alter.

“The latexes are in a state of Zen,” said Viswanath Meenakshisundaram, a fifth-year doctorate in mechanical engineering. student in the Design, Research and Education Laboratory for Additive Manufacturing Systems that collaborated with Scott. “If you add something to it, it will completely lose its stability and crash.”

Then the chemists came up with a new idea: what if Scott built a scaffold, similar to those used in building construction, around the latex particles to hold them in place? In this way, the latex could maintain its large 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 most important thing to worry about is the stability of everything,” Scott said. “It took a lot of reading, even things as basic as learning why colloids are stable and how colloidal stability works, but it was a really fun challenge.”

Novel development of engineering processing

While Scott was fiddling with the liquid latex, Meenakshisundaram had to figure out how to properly print the resin. The researchers chose to use a process called tub light-curing, in which the printer uses UV light to cure or harden a viscous resin in a specific way.

In need of a printer capable of printing high-resolution features over a large area, Meenakshisundaram built a new printer. He and Williams, his advisor, came up with the idea to scan ultraviolet light over a large area and, in 2017, they filed a patent for the printer.

Even with the custom printer, the fluid latex particles caused scattering away from the UV light projected onto the surface of the latex resin, resulting in the printing of inaccurate parts, so Meenakshisundaram came up with a novel second idea. He inserted a camera into the printer to capture an image of each tub of latex resin. With its custom algorithm, the machine can “see” the interaction of ultraviolet light on the resin surface, and then automatically adjust the print parameters to correct resin dispersion and cure only the desired shape.

“The large area scan printer was a concept I had, and Viswanath made it happen in no time,” said Williams. “Then Viswanath came up with the idea of ​​embedding a camera, observing how light interacts with material, and updating print parameters based on their code. That’s what we want from our PhD students: We provide insight and They achieve that and grow further as independent researchers. “

Meenakshisundaram and Scott discovered that their 3-D printed latex endpieces exhibited strong mechanical properties in a matrix known as a semi-interpenetrating polymer network, which had not been documented for elastomeric latexes in the prior literature.

“A network of interpenetrating polymers is like catching fish in a network,” said Meenakshisundaram. “The scaffolding shapes it. Once you put it in the oven, the water will evaporate and the tightly wound polymer chains can relax, spread or flow and penetrate the net.”

A Molecules Approach to Manufacturing

New advances in both development and materials processing highlight the interdisciplinary environment fostered between the two groups.

Long and Williams recognized the experience of their counterpart for making collective advance possible.

“My philosophy is that these kinds of innovations can only be achieved when you partner with people who are very different from you,” Long said.

The two professors said 3D printed latex provides the conceptual framework for printing an unprecedented range of materials, from rigid plastics to soft rubbers, which until now could not be printed.

“When I was a graduate student working on this technology, we were excited to get unique performance from the ways we could create, but the underlying assumption was that we had to settle for very poor materials,” Williams said. “What has been so exciting about this discovery with Tim’s group is being able to push the limit of what we assume was the limit of the performance of a printed material.”