Polymer discovery gives 3D-printed sand super strength

Date:
November 13, 2021
Source:
DOE/Oak Ridge National Laboratory
Summary:
Researchers 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.



FULL STORY ========================================================================== 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 study, published in Nature Communications, demonstrates a 3D-printed
sand bridge that at 6.5 centimeters can hold 300 times its own weight,
a feat analogous to 12 Empire State Buildings sitting on the Brooklyn
Bridge.

The binder jet printing process is cheaper and faster than other
3D-printing methods used by industry and makes it possible to create 3D structures from a variety of powdered materials, offering advantages
in cost and scalability. The concept stems from inkjet printing, but
instead of using ink, the printer head jets out a liquid polymer to
bind a powdered material, such as sand, building up a 3D design layer
by layer. 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.

Parts printed via binder jetting are initially porous when removed from
the print bed. They can be strengthened by infiltrating the design with
an additional super-glue material called cyanoacrylate that fills in
the gaps.

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.



==========================================================================
"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," said ORNL's Tomonori Saito, a lead
researcher on the project.

Parts formed with conventional binders are made denser with infiltrate materials, such as super glue, but none have reached close to the
performance of the PEI binder. The PEI binder's impressive strength stems
from the way the polymer reacts to bond with cyanoacrylate during curing.

One potential application for the super-strength sand is to advance
tooling for composites manufacturing.

Silica sand is a cheap, readily available material that has been gaining interest in automotive and aerospace sectors for creating composite parts.

Lightweight materials, such as carbon fiber or fiberglass, are wrapped
around 3D-printed sand cores, or "tools," and cured with heat. Silica
sand is attractive for tooling because it does not change dimensions when heated and because it offers a unique advantage in washable tooling. In composite applications, using a water-soluble binder to form sand tools
is significant because it enables a simple washout step with tap water
to remove the sand, 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.

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. Stronger
sand parts are needed to support manufacturing at a large scale and
enable rapid part production.

"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.

The journal article is published as "Additive manufacturing of
strong silica sand structures enabled by polyethyleneimine binder." ========================================================================== Story Source: Materials provided by
DOE/Oak_Ridge_National_Laboratory. Note: Content may be edited for style
and length.


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

Link to news story: https://www.sciencedaily.com/releases/2021/11/211113072456.htm

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