One of the biggest hurdles in 3D printing, or additive manufacturing, is the development of materials that can be 3D-printed without compromising their performance. Some materials have proven more difficult to print than others, including latex. But researchers at Virginia Tech have demonstrated a technique that could help solve this problem.
Latex is widely used in various products from gloves to paint and even some printing inks. The term ‘latex’ refers to a group of polymers — long, repeating chains of molecules — coiled inside nanoparticles dispersed in water. 3D printed latex and other similarly rubbery materials called elastomers could be used for a variety of applications, including soft robotics, medical devices, or shock absorbers.
However, as Viswanath Meenakshisundaram, a fifth-year mechanical engineering Ph.D. student in the Design, Research, and Education for Additive Manufacturing Systems Lab, explains: “Latexes are in a state of zen. If you add anything to it, it’ll completely lose its stability and crash out.”
The solution was to build a scaffold, similar to those used in building construction, around the latex particles to hold them in place so that photoinitiators and other compounds could be added to the latex to enable 3D printing with ultraviolet light.
Phil Scott, a fifth-year macromolecular science and engineering student in the Long Research Group, explained: “When designing the scaffold, the biggest thing you have to worry about is stability of everything.” He added: “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.”
Meanwhile, Meenakshisundaram built a 3D printer that uses a vat photopolymerization process, in which the printer uses UV light to cure a viscous resin into a specific shape. This was able to scan the UV light across a large area.
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 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.
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.
According to Meenakshisundaram, “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.”
Details of their initial results are detailed in a journal article published in ACS Applied Materials & Interfaces. In addition, the theory behind this 3D printing of latex could provide the conceptual framework for printing a range of other materials from rigid plastics to soft rubbers that have been difficult to print.
This research was carried out by an interdisciplinary team affiliated with the Macromolecules Innovation Institute (MII), the College of Science, and the College of Engineering, all departments of Virginia Tech polytechnic and university, based in Virginia, USA. It was funded by a National Science Foundation award aligned with the Grant Opportunities for Academic Liaison with Industry program, which supports teamed research between academia and industry, which in this case was a collaboration between Virgina Tech and Michelin North America. You can find more information from vt.edu.