The new plant-derived composites are as strong as bones and as hard as aluminum.

Designed by the MIT team, the new wood composites are bone-hard, aluminum-durable, and have the potential to pave the way for naturally occurring plastics. This image shows a tooth printed by a team resting on a background of tree cells.Credit: Massachusetts Institute of Technology

The strongest part of the tree is not in its trunk or vast roots, but in its fine cell walls.

The single wooden cell wall is the most abundant polymer in nature and is composed of cellulose fibers, the major structural constituents of all plants and algae.Reinforced in each fiber Cellulose nanocrystals, Or CNC is a chain of organic polymers arranged in an almost perfect crystalline pattern. At the nanoscale, CNC is stronger and more rigid than Kevlar. If crystals can be processed into a material in a significant proportion, CNC could be a stronger, more sustainable and path to naturally occurring plastics.

Currently, the MIT team has designed composites primarily made by mixing cellulose nanocrystals with small amounts of synthetic polymers. Organic crystals make up about 60-90% of the material. This is the highest percentage of CNC achieved with composites to date.

Researchers have found that cellulosic-based composites are stronger and stronger than certain bones, and harder than typical aluminum alloys. This material has a fine structure of bricks and mortar that resembles nacre. This is the hard inner shell lining of some mollusks.

The team came up with a recipe for a CNC-based composite that can be manufactured using both 3D printing and traditional casting. They printed the composite and cast it on a penny-sized film and used it to test the strength and hardness of the material. They also machined composites into tooth shapes, which one day used to make cellulosic-based dental implants, and for that matter, stronger, stronger, and more sustainable plastic products. Showed that it could be done.

“By using CNCs at high loads to create composites, we can give polymer-based materials unprecedented mechanical properties,” said A. John Hart, a professor of mechanical engineering. increase. “If we could replace petroleum-based plastics with naturally occurring cellulose, it would definitely be good for the planet.”

Hart and his team (including Abhinav Rao Ph.D.) ’18, Thibaut Divoux and Crystal Owens SM ’17 published their results in the journal today. cellulose..

The new plant-derived composites are as strong as bones and as hard as aluminum.

Caption: The team came up with a recipe for a CNC-based composite that can be manufactured using both 3D printing and traditional casting.Credit: Massachusetts Institute of Technology

Gel binding

Each year, over 10 billion tons of cellulose are synthesized from the bark, trees and leaves of plants. Most of this cellulose is used in the production of paper and textiles, and some is processed into powder for use in food thickeners and cosmetics.

In recent years, scientists have been exploring applications for cellulose nanocrystals that can be extracted from cellulose fibers by acid hydrolysis. Very strong crystals can be used as a natural reinforcement for polymer-based materials. However, because crystals tend to aggregate and bond to polymer molecules weakly, researchers have been able to incorporate only a small portion of the CNC.

Hart and his colleagues considered developing a composite material that has a high percentage of CNC and can be molded into strong and durable shapes. They started by mixing a solution of synthetic polymer with a commercially available CNC powder. The team determined the ratio of CNC to polymer that would turn the solution into a gel. This ratio can be supplied from the nozzle of a 3D printer or poured into a mold for casting. They used ultrasonic probes to break down the cellulose masses in the gel, increasing the likelihood that the dispersed cellulose would form strong bonds with the polymer molecules.

They sent a portion of the gel to a 3D printer and poured the rest into a mold for casting. Then let the printed sample dry. In the process, the material shrank, leaving a solid composite consisting primarily of cellulose nanocrystals.

“We basically dismantled and rebuilt the wood,” says Lao. “We have adopted the best components of wood, cellulose nanocrystals, and rebuilt them to create new composites.”

The new plant-derived composites are as strong as bones and as hard as aluminum.

The team carves a composite material into the shape of a tooth, which will one day be used to make stronger, stronger, more sustainable wood-derived dental implants, and for that matter, any plastic product. Showed that there is a possibility.Credit: Massachusetts Institute of Technology

Tough crack

Interestingly, when the team examined the structure of the composite under a microscope, they found that the cellulose particles were settled in the pattern of the physical store, similar to the structure of the nacre. In the nacre, this zigzag microstructure prevents cracks from passing straight through the material. Researchers have found that this also applies to their new cellulose composites.

They tested the resistance of the material to cracks, first using tools to initiate nanoscale and then microscale cracks. They found that the placement of cellulose particles in the composite, across multiple scales, prevented cracks from splitting the material.This resistance Plastic deformation It gives hardness and rigidity to composites at the boundary between traditional plastics and metals.

Going forward, the team is looking for ways to minimize shrinkage as the gel dries. Shrinkage is less of an issue when printing small objects, but as the composition dries, larger ones can buckle or crack.

“If we can avoid shrinkage, we can probably continue to scale up to the metric scale,” says Rao. “Then, if you have a big dream, you can replace a significant portion of the plastic with: cellulose Composite. ”

Nanocrystals from recycled wood waste make carbon fiber composites stronger

For more information:
Abhinav Rao et al, Printable, Castable, Nanocrystalline Cellulose-Epoxy Composite, Shows Hierarchical Nacre-like Reinforcement, cellulose (2022). DOI: 10.1007 / s10570-021-04384-7

Quote: The new plant-derived composite is as strong as bone and as hard as aluminum (February 10, 2022). .html

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The new plant-derived composites are as strong as bones and as hard as aluminum.

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