For hundreds of years cellulose has been used as a basis to create paper. New research from MIT now suggests it’s also the perfect material for renewable and ecologically friendly 3D printing.
“Cellulose is the most abundant organic polymer in the world,” says MIT post-doctorate Sebastian Pattinson, one of the authors of the paper about the new system that has been published in the journal Advanced Materials Technologies.
According to Pattinson Cellulose is “the most important component in giving wood its mechanical properties. 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 (3D printing) enables.”
As of today, 3D printing technology is greatly developing. Some of its many advantages are that it “allows you to individually customize each product you make,” Pattinson says.
The idea to use cellulose as a manufacturing material manufacturing is not new. In fact, many researchers that have attempted to harness it failed. When heated, cellulose thermally falls apart before it becomes flowable. The so called intermolecular bonding also makes high-concentration cellulose solutions too viscous to easily extrude.
Instead, the team at MIT made the decision to work with cellulose acetate — a material that is easy to make from cellulose and is already widely available. Essentially, the number of hydrogen bonds in this material has been reduced by the acetate groups. Cellulose acetate can be dissolved in acetone and extracted via a nozzle. As the acetone evaporates, the cellulose acetate solidifies in place. A subsequent optional treatment can replace the acetate groups and increase the strength of any printed parts.
“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” for 3-D printing, including acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA).
To demonstrate the potential of the new production process, the researchers added a small amount of antimicrobial dye to the cellulose acetate ink. This allowed them to create a 3D-printed pair of antimicrobial surgical tweezers.
“We demonstrated that the parts kill bacteria when you shine fluorescent light on them,” Pattinson says. Such custom-made tools “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. And with the antimicrobial properties, if the sterility of the operating room is not ideal the antimicrobial function could be essential,” he says.
Since most existing 3D printers require the heating of a polymer to make it flow, their production speed is limited by the amount of heat that can be delivered to the polymer without damaging it. This room-temperature cellulose process, which simply relies on evaporation of the acetone to solidify the part, could potentially be much faster.
Cellulose acetate is already widely available in consumer goods. In bulk, the material is comparable in price to that of plastics used for injection molding, and it’s much less expensive than the standard materials used for 3D printing today, the researchers say. This, combined with the room-temperature conditions of the process and the ability to provide cellulose with special properties, make the technology commercially attractive as well.