Researchers at the Department of Energy’s Oak Ridge National Laboratory designed a novel polymer to bind and strengthen silica sand for binder jet additive manufacturing, a 3D-printing method used by industries for prototyping and part production. The printable polymer enables sand structures with intricate geometries and exceptional strength – and is also water soluble. The binding polymer is what gives the printed sand its strength. The team used polymer expertise to tailor a polyethyleneimine, or PEI, binder that doubled the strength of sand parts compared with conventional binders. This second step provided an eight-fold strength increase on top of the first step, making a polymer sand composite stronger than any other and any known building materials, including masonry. “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. Current sand casting molds and cores have limited industrial use because commercial methods, such as washout tooling, apply heat and pressure that can cause sand parts to break or fail on the first try.

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