Reinforced polymers with ultra-thin carbon fiber fibers epitomize composite materials that are “light as feather and strong as steel”;, gaining those versatile applications in some industries. Adding materials called carbon nanotubes can further increase the performance of the components. But the chemical processes used to incorporate carbon nanotubes end up spreading them unevenly in the composition, limiting the strength and other useful qualities that can eventually be achieved.
In a new study, researchers at the University of Texas at A&M have used a natural plant product, called cellulose nanocrystals, to seamlessly bond and wrap carbon nanotubes into carbon fiber composites. The researchers said that their described method is faster than conventional methods and also allows the design of carbon fiber composites from nanosca.
The results of the study were published online in the journal American Chemical Society (ACS) Nano applied materials.
Composites are built in layers. For example, polymer compounds are made from layers of fibers, such as carbon fiber or Kevlar, and a polymer matrix. This stratified structure is the source of component weakness. Damagedo layer damage causes fractures, a process technically known as delamination.
To increase the strength and give carbon fiber composites other desirable qualities, such as electrical and thermal conductivity, carbon nanotubes are often added. However, the chemical processes used to incorporate carbon nanotubes into these compounds often cause nanoparticles to accumulate, reducing the overall benefit of adding these particles.
“The problem with nanoparticles is similar to what happens when you add thick coffee powder to milk – the powder agglomerates or sticks to each other,” said Dr. Amir Asadi, Assistant Professor in the Department of Engineering Technology and Industrial Distribution. “To take full advantage of carbon nanotubes, they must first be separated from each other, and then somehow designed to go to a specific location within the carbon fiber composition.”
To facilitate the even distribution of carbon nanotubes, Assad and his team turned to cellulose nanocrystals, an ingredient readily obtained from recycled wood pulp. These nanocrystals have segments in their molecules that attract water and other segments that repel water. This unique molecular structure offers the ideal solution for building nano-scale composites, Assad said.
The hydrophobic part of cellulose nanocrystals binds to carbon fibers and anchors them to the polymer matrix. Attractive water portions of nanocrystals, on the other hand, help distribute carbon fibers evenly, just as sugar, which is hydrophilic, dissolves evenly in water rather than accumulating and settling to the bottom of a cup.
For their experiments, the researchers used a commercially available carbon fiber cloth. To this cloth, they added an aqueous solution of cellulose nanocrystals and carbon nanotubes and then applied strong vibrations to mix all the items together. Finally, they let the material dry and spread resin on it to gradually form the polymer composite coated with carbon nanotubes.
After examining a composite sample using electron microscopy, Assad and his team observed that cellulose nanocrystals attached to the tops of carbon nanotubes, orienting the nanotubes in the same direction. They also found that cellulose nanocrystals increased the composite’s resistance to bending by 33% and its inter-laminar strength by 40% based on measurement of the mechanical properties of the material under extreme load.
“In this study, we took the way of composing nanosca composites using cellulose nanocrystals. This method has allowed us to have more control over the properties of polymer composites coming out in macroscale,” Assad said. “We think our technique is a way forward in escalating the processing of hybrid composites, which will be beneficial to a variety of industries, including airlines and vehicle manufacturing.”
Both carbon plants and nanotubes can improve cars
Shadi Shariatnia et al, Nanocrystalline bonded carbon nanotubes / Carbon fiber polymer complexes for structural applications, Applied Nano Materials ACS (2020). DOI: 10.1021 / acsanm.0c00785
Provided by Texas A&M University
citation: Nanocrystals from recycled wood waste make tougher carbon fiber composites (2020, August 12) taken on August 12, 2020 from https://phys.org/news/2020-08-nanocrystals-recycled-wood- carbon-fiber-composites.html
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