New 3D printing materials are constantly being developed, as scientists strive to come up with material that’s stronger, more versatile, more sustainable, etc. Materials development isn’t a simple process, but it helps when you’re working with a resource that’s as readily attainable as cellulose – the “most abundant organic polymer in the world,” says MIT postdoc Sebastian Pattinson.
Pattinson, along with associate professor of mechanical engineering and MIT Mechanosynthesis Group head A. John Hart, recently published a National Science Foundation-supported study entitled “Additive Manufacturing of Cellulosic Materials With Robust Mechanics and Antimicrobial Functionality,” which you can access here. Cellulose, the main component of plant cell walls, is everywhere, in the natural world and in the plant-based materials that we use every day: paper, wood, cotton, etc. If it’s not petroleum-based, i.e. plastic or polyester, it’s likely cellulose-based (or metal), and what Pattinson and Hart are trying to do is to replace the non-renewable plastics so commonly used in 3D printing with the much more environmentally friendly cellulose.
“[Cellulose is] the most important component in giving wood its mechanical properties,” explains Pattinson. “And because it’s so inexpensive, it’s biorenewable, biodegradable, and also very chemically versatile, it’s used in a lot of products. Cellulose and its derivatives are used in pharmaceuticals, medical devices, as food additives, building materials, clothing — all sorts of different areas. And a lot of these kinds of products would benefit from the kind of customization that additive manufacturing enables.”
Pattinson and Hart aren’t the first to think so – several other institutions have been conducting serious research into cellulose as a 3D printing material – it’s even been tossed around as a possible component of 3D printed food in the future. It’s a challenging material to print, though. When heated, cellulose thermally decomposes, partly due to the hydrogen bonds between the cellulose molecules, which also make for a viscous, difficult to extrude material.
Cellulose acetate is a different matter. To create this already commonly-used material, pure cellulose is combined with acetic anhydride, which reduces the number of hydrogen bonds. Cellulose acetate can be dissolved in acetone and extruded through a nozzle; once the acetone evaporates, the cellulose acetate solidifies into a strong plastic alternative. The solidified cellulose acetate can then be further treated for an even stronger material, as Pattinson and Hart did.
“After we 3-D print, we restore the hydrogen bonding network through a sodium hydroxide treatment,” Pattinson says. “We find that the strength and toughness of the parts we get…are greater than many commonly used materials.”
That’s not the coolest part, though. Pattinson and Hart further experimented by adding an antimicrobial dye to the cellulose acetate and 3D printing a pair of surgical tweezers. When fluorescent light was shined on the tweezers, the antimicrobial properties activated and killed bacteria.
“[Tools like this] could be useful for remote medical settings where there’s a need for surgical tools but it’s difficult to deliver new tools as they break, or where there’s a need for customized tools,” says Pattinson. “And with the antimicrobial properties, if the sterility of the operating room is not ideal the antimicrobial function could be essential.”
Cellulose acetate could potentially be faster to print than polymer materials, he continues, as it’s a room-temperature process that only requires evaporation to solidify the material. It could even be further accelerated by blowing hot air over it to speed the evaporation process, for example. It’s also much less expensive than the polymer materials most commonly used for 3D printing, and it’s already widely available for other purposes. These factors, along with the material’s sustainability, could give cellulose acetate tremendous appeal for 3D printing – and giving Pattinson and Hart the honor of accomplishing what other materials scientists have been struggling to do. Discuss in the Cellulose forum at 3DPB.com.[Source: MIT News]
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