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Additive manufacturing of strong silica sand structures enabled by polyethyleneimine binder

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Nature Communications
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Additive manufacturing (AM) enables the creation of unparalleled structures out of common materials, and AM especially provides a path to producing customized tools and dies for industrial manufacturing. Binder jet AM (BJAM) is well suited for manufacturing these tools and dies due to its high production rates, low operator burden, high resolution, and ability to process low-cost feedstocks, such as sand. Here we report the discovery of a versatile binder, hyperbranched polyethyleneimine for BJAM, to produce extremely versatile structures and tools out of silica sand that provide exceptionally high strength, coupled with the ability for sacrificial washout and reactive infiltration. The use of polyethyleneimine binder doubled the flexural strength of BJAM printed parts to 6.28 MPa compared with that of the conventional binder, making it stronger than unreinforced concrete (~4.5 MPa). The high flexural strength arises from a corrugated interfacial structure formed by strong hydrogen-bonding. Furthermore, we demonstrate that the residual free amine groups in the printed parts can be reacted with cyanoacrylate through a secondary infiltration, resulting in an unprecedented increase in flexural strength to 52.7 MPa, which is greater than common construction materials such as brick and mortar.