Cellulose Revolution in 3-D Printing

Cellulose Revolution in 3-D Printing

Cellulose has formed the basis of the world's most abundantly printed material for centuries—namely paper. Cellulose is now poised, thanks to new research at MIT, to potentially offer a renewable, biodegradable alternative to polymers currently used in 3-D printing materials. Sebastian Pattinson, an MIT postdoctoral researcher and lead author of an article explaining the new system in Advanced Materials Technologies journal, states: "Cellulose is the most abundant organic polymer in the world." A co-author of this article is A. John Hart, Associate Professor of Mechanical Engineering at the Mitsui Career Development Center for Contemporary Technology. Pattinson explains: "Cellulose is the most important component in giving wood its mechanical properties." And because it is very inexpensive, biologically renewable, biodegradable, and chemically versatile for use in many products, it can be employed in a wide range of applications. Cellulose and its derivatives are used in different fields such as pharmaceuticals, medical devices, food additives, construction materials, and textiles. And these types of product varieties will benefit from the customization method that enables additive manufacturing, namely 3-D printing. Meanwhile, 3-D printing technology is growing rapidly. Pattinson states that, among other advantages, it "allows you to customize each product you make individually." Using cellulose as a material for additive manufacturing is not a new idea; many researchers have attempted it but have encountered major obstacles.

When cellulose is heated, it thermally degrades before becoming fluid due to hydrogen bonds between cellulose molecules. Intramolecular bonding also makes highly concentrated cellulose solutions too viscous to be easily extruded.

Instead, the MIT team chose to work with cellulose acetate, a material easily derived from cellulose and already produced and readily available. Essentially, the number of hydrogen bonds in this substance has been reduced by acetate groups. Cellulose acetate can be dissolved in acetone and extruded through a nozzle. As acetone rapidly evaporates, cellulose acetate solidifies in place. Subsequently, optional post-processing replaces the acetate groups and increases the strength of the printed parts. To demonstrate the chemical versatility of the production process, Pattinson and Hart added an additional dimension to the innovation. By adding a small amount of antimicrobial dye to cellulose acetate ink, they 3-D printed a pair of surgical tweezers with antimicrobial functionality. Since most current extrusion-based three-dimensional printers rely on heating the polymer to make it flow, production speeds are limited by the amount of heat the polymer can withstand without damage. For this reason, Pattinson noted that the cellulose process, which can take place at room temperature and is based on acetone evaporation and solidifying the part, could potentially be faster. Moreover, various methods such as arranging thin strips to maximize surface area, for example, or blowing hot air to accelerate evaporation could further speed up the process. In order to make this process even more cost-effective and environmentally friendly, recovery of the evaporated acetone is also a possibility.