Nanocrystals from recycled wood waste make compositions with carbon fiber harder

Polymers reinforced with ultrafine strands of carbon fibers form composite materials that are “light as a feather and strong as steel”, and they are versatile applications in various industries. Addition of materials called carbon nanotubes can further improve the functionality of the compositions. But the chemical processes used to incorporate carbon nanotube disperse them unevenly into the composites, limiting the strength and other useful qualities that can eventually be achieved.

In a new study, researchers from Texas A&M University used a natural plant product, called zero-crystalline cellulose, to uniformly pinch carbon nanotubes and coat them on the composite carbon fiber. The researchers said that their prescribed method is faster than conventional methods and allows the design of carbon fiber composites from the nanoscale as well.

The results of the study are published online in the journal American Chemical Society (ACS) Tapaste nano-materials.

Composites are built in layers. For example, polymer composites are made of layers of glass fiber, such as carbon fibers such as Kevlar, and a polymer matrix. This layered structure is the source of the weak composites. Any damage to the layers causes fractures, a process technically known as delamination.

To increase strength and give carbon fiber compositions other desirable qualities, such as electrical and thermal conductivity, carbon nanotubes are often added. However, the chemical processes used to incorporate the carbon nanotubes into these composites often cause the nanoparticles to clump up, which reduces the great benefit of adding these particles.

“The problem with nanoparticles is similar to what happens when you add coarse coffee powder to milk – the powder agglomerates stick together,” said Dr Amir Asadi, assistant professor in the Department of Engineering Technology and Industrial Distribution. “To fully utilize the carbon nanotubes, they must first be separated from each other, and then somehow designed to move to a specific location in the carbon fiber composition.”

To facilitate the equal distribution of carbon nanotubes, Asadi and his team turned to nanocrystals of cellulose, a compound easily obtained from recycled wood pulp. These nanocrystals have segments on their molecules that attract water and other segments that are repelled by water. This unique molecular structure provides the ideal solution to construct composites on the nanoscale, Asadi said.

The hydrophobic part of the nanocrystals of cellulose binds to the carbon fibers and anchors them to the polymer matrix. On the other hand, the water-attractive parts of the nanocrystals help to disperse the carbon fibers evenly, just like how sugar, which is hydrophilic, dissolves in uniform water instead of clumping and settling to the bottom of a beaker.

For their experiments, the researchers used a commercially available carbon fiber cloth. To this cloth she added an aqueous solution of nanocrystals of cellulose and carbon nanotubes and then applied strong vibrations to mix all the items together. Finally, they allowed the material to dry and spread resin on it to gradually form the carbon compound composed of carbon nanotube.

Examining a sample of the composite using electron microscopy, Asadi and his team found that the nanocrystals of cellulose were directed at the tips of the carbon nanotubes, and oriented the nanoburners in the same direction. They also found that cellulose nanocrystals increased the composite’s resistance to bending by 33% and its interlaminar strength by 40% based on measuring the mechanical properties of the material under extreme load.

“In this study, we took the approach of designing the nanoscale composites with cellulose nanocrystals. This method has allowed us to have more control over the properties of the polymer composites that emerge on the macro scale,” sei Asadi. “We think our technology is a way forward in scaling up the processing of hybrid composites, which will be useful for a variety of industries, including aerospace and automotive manufacturing.”