Researchers at the Massachusetts Institute of Technology continue to innovate when it comes to creating new materials. Two different groups of chemical engineers at MIT recently revealed their respective work–– one involving a new type of lightweight, super-strong plastic, and the other a composite made mostly from cellulose nanocrystals mixed with a bit of synthetic polymer.
The first project involves using a novel polymerization process to create a new material that the researchers say is stronger than steel, as light as plastic and can be easily manufactured in large quantities. It is a two-dimensional polymer that self-assembles into a sheet called a polyaramide.
This is unlike all other polymers, which form one-dimensional, spaghetti-like chains. Until now, states MIT, scientists had believed it was impossible to induce polymers to form 2D sheets.
This entirely new type of plastic, which they’ve given the snappy name of 2DPA-1, is twice as strong as steel under load tests, with just one-sixth the material bulk, according to Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT and the senior author of the new study, which was published on Feb. 2 in the journal Nature. MIT postdoctoral fellow Yuwen Zeng is the study’s lead author.
The researchers –– who have filed for two patents on the process they used to generate the material –– say the material also can conduct electricity and block gas. Such a material, notes Strano, could be used as a lightweight, durable coating for car parts or cell phones or as a building material for bridges or other structures.
In an interview with Fast Company, Strano explains it this way: “Think of a plate of spaghetti: The sauce goes deep inside.” 2DPA-1, on the other hand, arranges its polymers as flat discs rather than 3D spaghetti, he continued. Laid out like a one-molecule-thick sheet of paper, these discs link to one another with the strongest molecule-to-molecule bond in nature: the hydrogen bond. Strano compared it to “2D Kevlar.”
Another big potential advantage of 2DPA-1 is that it can be bulk produced relatively easily, in much the same manner as other plastics. Because the material self-assembles in solution, it can be made in large quantities by simply increasing the quantity of the starting materials.
All about cellulose nanocrystals
Meanwhile, elsewhere at MIT, A. John Hart and his team published the results of their composites work on Feb. 10 in the journal Cellulose. Hart is a professor of mechanical engineering, director of MIT’s Laboratory for Manufacturing and Productivity, and director of its Center for Additive and Digital Advanced Production Technologies.
He and his research group have engineered a composite that consists of 60-90% cellulose nanocrystals (CNCs) — said to be the highest fraction of CNCs achieved in a composite to date.
They state in their report that “Due to their exceptional mechanical and chemical properties and their natural abundance, cellulose nanocrystals are promising building blocks of sustainable polymer composites. However, the rapid gelation of CNC dispersions has generally limited CNC-based composites to low CNC fractions, in which polymer remains the dominant phase. Here we report on the formulation and processing of crosslinked CNC-epoxy composites with a CNC fraction exceeding 50 wt%.”
Hart and his team say the new cellulose-based composite is stronger and tougher than some types of bone and harder than typical aluminum alloys, such as DuPont’s Kevlar aramid fiber. They add that their recipe for this composite can be fabricated using both 3D printing and conventional casting. Essentially, the team said, they “basically deconstructed wood, and reconstructed it.”
The researchers’ goal was to develop a composite with a high fraction of CNCs that they could shape into strong, durable forms. Composites World quoted Hart as saying that “By creating composites with CNCs at high loading, we can give polymer-based materials mechanical properties they never had before. If we can replace some petroleum-based plastic with naturally derived cellulose, that’s arguably better for the planet as well.”
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