A water-soluble novel polymer designed by researchers at Oak Ridge National Laboratory (ORNL) binds silica sand for 3D-printing for molds, prototypes, and part production in industries such as automotive and aviation.  

The ORNL team created a polyethyleneimine (PEI) binder that doubled the strength of sand parts compared with conventional binders. Initially porous, binder jet printed parts are strengthened by adding cyanoacrylate to fill gaps, providing eight times the strength when compared to the initial output. The PEI binder is strengthened by the reaction of the polymer to bind with the cyanoacrylate during curing. 

Tomonori Saito, a lead ORNL researcher on this study, explained, “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.”  

Not only is the material strengthened by the 3D layer-by-layer printing, the binder jet printing process saves money and speeds the printing process.  

Silica sand is easily available and is inexpensive and does not change dimensions when heated, making it a strong choice for washable tooling, but current sand-casting molds have limited use because they often break. ORNL’s new PEI binder changes that situation by strengthening the molds and parts.  

“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 lead author of the study Dustin Gilmer, a student at the University of Tennessee Bredesen Center. “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.”