Researchers Develop Binding Polymer That Gives 3D-Printed Sand Super Strength

In a new technological breakthrough, a team  of researchers from the Department of Energy’s Oak national Laboratory has designed a polymer that can bind and strengthen silica sand that will be used for binder jet addictive manufacturing.

The 3D-printing method that had hitherto been used by industries for prototyping and part production has the water soluble polymer having the leverage to enable sand structures with convoluted geometrics and atypical strength.

The new study published in popular science journal, Nature Communications, and licensed by industry partner ExOne for research, displays a 6.5 centimeters 3D-printed sand bridge that has the uncanny ability to hold 300 times its own weight.

In this process, the printer head releases a liquid polymer that is used to bind a powered material like sand to build up a 3D design layer by layer, with the binding polymer the source of the printed sand’s strength.

The team infused their polymeric expertise to attune polyethyleneimine, or PEI, binders that can double the strength of sand parts as compared with conventional binders.

In lieu of the fact that parts printed through the process of binder jetting will be porous when they are removed from the print bed, a super-glue material known as cyanoacrylate is then added to strengthen it. This will increase the strength at least eight times, in the process making the polymer sand composite stronger than any other and any known building materials, including masonry.

Oak Ridge National Laboratory scientist Tomonori Saito shows a 3D-printed sandcastle at the DOE Manufacturing Demonstration Facility at ORNL. Credit: Carlos Jones/ORNL, U.S. Dept. of Energy

Oak Ridge National Laboratory scientist and a lead researcher on the project,  Tomonori Saito, explained the process further when he said:

“Few polymers are suited to serve as a binder for this application. We were looking for specific properties, such as solubility, that would give us the best result. Our key finding was in the unique molecular structure of our PEI binder that makes it reactive with cyanoacrylate to achieve exceptional strength”.

The areas created with conventional binders are made to be more opaque with permeated materials like super glue but none of them has shown to perform like the PEI binder. The impressive strength of the PEI binder was as a result of the way the polymer reacts to bond with cyanoacrylate during curing.

The use of silica sand comes handy as it is readily available and cheap for use, becoming a subject of interest in the automotive and aerospace sectors, with its use in creating composite parts. Carbon fiber and other lightweight materials are laced around 3D-printed sand cores and cured with heat. A major reason Silica sand is good for tooling is because when heated, it doesn’t change dimensions, also have a distinct advantage in washable tooling. The use of a water-soluble binder in composite applications to form sand tools is vital as it allows a simple washout step with tap water to remove the sand, in the process leaving a hollow composite form.

“To ensure accuracy in tooling parts, you need a material that does not change shape during the process, which is why silica sand has been promising. The challenge has been to overcome structural weakness in sand parts,” said Dustin Gilmer, a University of Tennessee Bredesen Center student and the study’s lead author.

There are limited industrial use for sand casting moulds and cores as washout tooling and other commercial methods makes use of the application of heat and pressure to make sand parts to break and fail on the first try. To support manufacturing on a sizeable scale to allow rapid production, stronger sand parts will be required.

“Our high-strength polymer sand composite elevates the complexity of parts that can be made with binder jetting methods, enabling more intricate geometries, and widens applications for manufacturing, tooling, and construction,” said Gilmer.

The novel binder won a 2019 R&D 100 Award and has been licensed by industry partner ExOne for research.

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