For centuries, cellulose has formed the basis of the world's most abundant material on which to print: paper. Thanks to new research at the Massachusetts Institute of Technology (MIT), it may also become a material to print with. Cellulose could thus become a sustainable alternative to the polymers currently used.
"Cellulose is the most abundant organic polymer in the world," states Sebastian Pattinson, lead author of the study. "Cellulose and its derivatives are used in medicines, medical devices, food supplements, building materials, clothing. In short, for all kinds of (new) applications. Many of these products would benefit from the kind of customisation that additive manufacturing (3D printing) makes possible."
Acetate
Cellulose is largely responsible for the mechanical properties of wood It is renewable, biodegradable and chemically very versatile. Using cellulose as a material for additive manufacturing is not a new idea and many scientists have made an attempt to find a way to do this. However, most ran into obstacles. When cellulose is heated, it thermally dissolves before it becomes liquid. This is partly due to the hydrogen bonds between cellulose molecules.
MIT team instead used cellulose acetate, a material that is easy to make from cellulose and is already produced worldwide and widely available. The number of hydrogen bonds was reduced by the acetate groups. Cellulose acetate can be dissolved in acetone and extruded through a nozzle. The acetone evaporates rapidly, solidifying the material. An optional additional treatment in which the acetate groups are replaced can then strengthen the printed part.
Extra dimension
"After we 3D print, we restore the hydrogen-bonded network through sodium hydroxide treatment," Pattinson says. He adds that the strength and strength of the final parts are better than those of most commonly used 3D printing materials, including ABS and PLA.
To demonstrate the chemical versatility of the production process, the researchers added an extra dimension to the innovation. For instance, they added an antimicrobial dye to the vegetable ink and printed a pair of antibacterial surgical tweezers. These tweezers killed most of the bacteria when exposed to fluorescent light. According to MIT, such custom-made surgical tools "could be useful for remote medical institutions where broken tools are difficult to replace or where there is a need for custom-made supplies". Moreover, the antimicrobial function may be essential in an operating theatre where sterility is not optimal.
Because most existing extruding 3D printers work on the basis of heating polymer to liquefy it, production speed is limited because polymer can only handle a certain amount of heat without damaging. The advantage of the new process developed by MIT and its reliance on the evaporation of acetone to strengthen the printed part is that it can be carried out at room temperature. This can provide a faster printing process. In addition, the wide availability and low cost of cellulose worldwide may make the material commercially attractive.
By: Kelly Bakker
Source photos: scientists MIT.
