Plant-based solid matter: Can replace plastic, can be used in 3D printing or molding

A single wood cell is made up of fibers of cellulose - the tough natural polymer that is the building block of all plants. Within each fiber are reinforced cellulose nanocrystals (reinforcing cellulose nanocrystal, or CNC); they are chains of organic polymers arranged in sub-perfect crystal formations.

At the nanoscale, CNC is tougher than Kevlar armor, and has the potential to produce more resilient, more environmentally friendly natural plastics.

A layer of cellulose nanocrystals in a petri dish.

To that end, a team of researchers at MIT created a synthetic substance made of cellulose crystals combined with a bit of an artificial polymer. The number of organic crystals accounts for 60-90% of the material's composition; Scientists also set a record when creating the most CNC-containing matter ever.

The new material is stronger than some solid forms of bone, and also tougher than the aluminum alloys still used in the fabrication. The microstructure of the new material is comparable to the glossy white mother-of-pearl commonly found in the shells of mollusks.

Glossy white nacre in the shell.

The new CNC compound formulation allows scientists to both 3D print matter and mold it in the usual way. 'By creating a compound that contains a large amount of CNC, we are able to introduce unprecedented properties into polymer-based materials,' said A. John Hart, a professor working on the new project.

'If we could replace petroleum-based plastics with natural-based cellulose, that would be able to improve [the well-being of] the planet'.

A flexible assembly

Each year, industrial production lines synthesize more than 10 tons of cellulose from the bark, wood and leaves of plants. Most of them are used in the production of paper or textiles, a small part are used in food processing or cosmetics.

The wood lignin contains cellulose nanocrystals.

In recent years, science has begun to pay attention to the nanocrystal structure of cellulose, which can be easily extracted by acid hydrolysis. However, the effort to add CNC to the material still faces many obstacles, as this crystal tends to clum, not firmly clinging to polymer molecules.

Professor Hart and colleagues are still struggling to find a way to create a composite material containing high levels of CNC, which can be easily molded into beneficial shapes. They plan to mix CNC and polymer into a pliable gel that can be used in 3D printers or poured into molds. Using ultrasonic technology to remove clumping, the team was able to help bind the adhesive together more effectively.

"We basically decomposed the wood and then reassembled it," said researcher Abhinav Rao. 'We take the best part of the wood, i.e. cellulose nanocrystals, and reconstruct them into a new composite material'.

Solid material

Exploring the structure of the compound under a microscope, the team discovered that cellulose particles had been arranged into a structure similar to the nacre found in the shells of many mollusks. Naturally, this structure will be more resistant to cracks, making the new material more solid.

The block is 3D printed from a new material, with solid properties similar to industrial aluminum.

When put to the test, the team found that the cellulose particles kept the material from breaking in half despite cracking. The resistance makes the material a potential compound, bringing in the rigidity and toughness of both metal and plastic.

In the near future, the team continues to find ways to limit the material's volume loss when solidified. On a large scale, volume reduction can destabilize an object's structure.

'If we can prevent the material from shrinking, we can continue to scale up the project, with objects up to meters in size,' researcher Rao said. "If the apricots are big enough, we can even replace a significant portion of the plastic with synthetic cellulose."