A research team from Massachusetts Institute of Technology (MIT) announced it has engineered a composite made mostly from cellulose nanocrystals (CNC) mixed with a bit of synthetic polymer. The researchers found the cellulose-based composite is stronger and tougher than some types of bone.
In a study published Feb.13 in the journal Cellulose, the team hit on a recipe for the CNC-based composite that they could fabricate using both 3D printing and conventional casting. They printed and cast the composite into small pieces that they used to test the material's strength and hardness. They also machined the composite into the shape of a tooth to show that the material might one day be used to make cellulose-based dental implants.
The strongest part of a tree lies not in its trunk or its sprawling roots, but in the walls of its microscopic cells, explained the researchers.
A single wood cell wall is constructed from fibers of cellulose -- nature's most abundant polymer, and the main structural component of all plants and algae. Within each fiber are reinforcing cellulose nanocrystals, or CNCs, which are chains of organic polymers arranged in nearly perfect crystal patterns.
At the nanoscale, CNCs are stronger and stiffer than Kevlar. If the crystals could be worked into materials in significant fractions, CNCs could be a route to stronger, more sustainable, naturally derived plastics.
The team tested the material's resistance to cracks, and found that, across multiple scales, the composite's arrangement of cellulose grains prevented the cracks from splitting the material. This resistance gives the composite hardness and stiffness. They also examined the composite's structure under a microscope, they observed that grains of cellulose settled into a brick-and-mortar pattern, which stops a crack from running straight through the material.
MIT researchers believe these unique characteristics could help use cellulose in new and unfamiliar applications. Each year, more than 10 billion tons of cellulose is synthesized from the bark, wood, or leaves of plants. Most of this cellulose is used to manufacture paper and textiles, while a portion of it is processed into powder for use in food thickeners and cosmetics.
