Science & Technology

The discovery of binding polymers brings super-strength to 3D-printed sand

Developed at Oak Ridge National Laboratory, the new polymer reinforces sand for laminated molding applications. The 6.5 cm 3D printed sand bridge shown here held 300 times its own weight. Credits: Dustin Gilmer / University of Tennessee, Knoxville

Researchers at the Oak Ridge National Laboratory at the Department of Energy have designed a new polymer to bind and strengthen silica sand for the production of binder jet additives. This is the 3D printing method used in the industry for prototyping and component manufacturing.

Printable polymers allow for sand structures with complex shapes and extraordinary strength, and are also water soluble.

Research published in Nature CommunicationsShows a 3D-printed sand bridge that can hold 300 times its own weight at 6.5 centimeters. This is a feat similar to the 12 Empire State Buildings on the Brooklyn Bridge.

The binder jet printing process is cheaper and faster than other 3D printing methods used in the industry, and it has the advantage of cost and scalability because it can create 3D structures from a variety of powder materials. The concept comes from inkjet printing, but instead of using ink, the printer head sprays a liquid polymer to combine powdered materials such as sand to build a 3D design layer by layer. Bonded polymers give the printed sand its strength.

The team used polymer expertise to tune a polyethyleneimine (PEI) binder that doubles the strength of the sand compared to traditional binders.

Parts printed with a binder jet are initially porous when removed from the print bed. They can be reinforced by infiltrating the design with an additional superglue material called cyanoacrylate that fills the gap. This second step is eight times stronger than the first step, making the polymer sand composite stronger than other known building materials (including stone).

Tomonori Saito

Tomonori Saito, a scientist at Oak Ridge National Laboratory, is exhibiting a 3D-printed sand castle at ORNL’s DOE manufacturing demonstration facility.Credits: Carlos Jones / ORNL, US Department of Energy

“Few polymers are suitable to act as binders for this application. We were looking for specific properties that would give the best results, such as solubility. Our important finding was the unique molecular structure of PEI binders. “We have achieved exceptional strength by reacting with cyanoacrylates,” said Tomonori Saito of ORNL, a senior researcher at the project.

Parts made of traditional binders are denser with penetrating materials such as superglue, but none are close to the performance of PEI binders. The impressive strength of the PEI binder comes from the way the polymer reacts and binds to cyanoacrylate during curing.

One of the potential uses of ultra-strong sand is to advance tools for composite material manufacturing.

Quartz sand is an inexpensive and readily available material and is of interest in the automotive and aerospace fields for making composite parts. Lightweight materials such as carbon fiber and fiberglass are wrapped around a 3D-printed sand core, or “tool,” and heat-cured. Quartz sand is attractive to tools because it does not change its dimensions when heated and has the unique advantage of washable tools. In mixed-use, it is important to use water-soluble binders to form sand tools. This is because it can be easily rinsed with tap water to remove sand, leaving a hollow composite morphology.

“To ensure Accuracy Tooling parts require materials that do not change shape during the process. Therefore, quartz sand is promising. Dustin Gilmer, a student at the University of Tennessee Bredesen Center and lead author of the study, said:

Current sand casting molds and cores are for industrial use as commercial methods such as washout touring apply heat and pressure, which can damage or fail sand parts in the first attempt. Limited. Stronger sand parts are needed to support large-scale manufacturing and enable rapid parts production.

“Our high-strength polymer sand composites increase the complexity of the parts that can be manufactured by the binder injection method, allowing for more complex shapes and expanding their manufacturing, tooling and construction applications,” Gilmer said.

This new binder has won the 2019 R & D 100 Award and is research licensed from industry partner ExOne.

Reference “Laminate molding of strong silica sand structure made possible by polyethyleneimine binder” Dustin B. Gilmer, Lu Han, Michelle L. Lehmann, Derek H. Siddel, Guang Yang, Azhad U. Chowdhury, Benjamin Doughty, Amy M. Elliott, Tomonori Saito, August 26, 2021 Nature Communications..
DOI: 10.1038 / s41467-021-25463-0

This work used resources sponsored by the DOE Energy Efficiency and Renewable Energy Department and supported by the DOE Science Department.

The discovery of binding polymers brings super-strength to 3D-printed sand The discovery of binding polymers brings super-strength to 3D-printed sand

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