Humans have printed on paper for centuries. But now MIT researchers have found a way to print with cellulose, paper’s primary ingredient. The world’s most abundant organic polymer, and the main one that gives wood its mechanical properties, cellulose is inexpensive, biorenewable, biodegradable, and very chemically versatile.
Previous attempts to use cellulose for 3-D printing have been limited because heated cellulose thermally decomposes before it becomes able to flow, and high-concentration cellulose solutions are too viscous to be easily extruded.
The MIT team works with cellulose acetate. This material, which is easily made from cellulose by acetylating some of its hydroxyl groups, can be dissolved in acetone and extruded through a nozzle. After extrusion, the acetone quickly evaporates and the cellulose acetate solidifies in place. A subsequent optional treatment replaces the acetate groups with groups found on the original cellulose molecule to strengthen the printed parts.
“After we 3-D-print, we restore the hydrogen bonding network through a sodium hydroxide treatment,” says postdoc Sebastian Pattinson, who coauthored a paper on the research with associate professor A. John Hart in Advanced Materials Technologies. He says the results are stronger and tougher than many materials commonly used for 3-D printing, including acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA).
Because most existing extrusion-based 3-D printers rely on heating 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. The new room-temperature cellulose process, which relies on evaporation of the acetone to solidify the part, could potentially be faster, Pattinson says.