Renewable cellulose crystals are as stiff as steel
The same tiny cellulose crystals that give trees and plants their strength and light weight could be used to create a new type of tough, renewable material.
Calculations using precise models based on the atomic structure of cellulose show the crystals have a stiffness of 206 gigapascals, which is comparable to steel, says Pablo D. Zavattieri, a Purdue University assistant professor of civil engineering.
“This is a material that is showing really amazing properties,” he says. “It is abundant, renewable, and produced as waste in the paper industry.”
Findings are detailed in the journal Cellulose.
“It is very difficult to measure the properties of these crystals experimentally because they are really tiny,” Zavattieri says. “For the first time, we predicted their properties using quantum mechanics.”
Create lots of biodegradable stuff
The nanocrystals are about 3 nanometers wide by 500 nanometers long—or about 1/1,000th the width of a grain of sand—making them too small to study with light microscopes and difficult to measure with laboratory instruments.
The findings represent a milestone in understanding the fundamental mechanical behavior of the cellulose nanocrystals.
“It is also the first step towards a multiscale modeling approach to understand and predict the behavior of individual crystals, the interaction between them, and their interaction with other materials,” Zavattieri says.
“This is important for the design of novel cellulose-based materials as other research groups are considering them for a huge variety of applications, ranging from electronics and medical devices to structural components for the automotive, civil, and aerospace industries.”
The cellulose nanocrystals represent a potential green alternative to carbon nanotubes for reinforcing materials such as polymers and concrete.
Cellulose biomaterials might be used to create biodegradable plastic bags, textiles and wound dressings; flexible batteries made from electrically conductive paper; new drug-delivery technologies; transparent flexible displays for electronic devices; special filters for water purification; new types of sensors; and computer memory.
Cellulose could come from a variety of biological sources including trees, plants, algae, ocean-dwelling organisms called tunicates, and bacteria that create a protective web of cellulose.
“With this in mind, cellulose nanomaterials are inherently renewable, sustainable, biodegradable, and carbon-neutral like the sources from which they were extracted,” says Robert J. Moon, a researcher from the US Forest Service’s Forest Products Laboratory and study co-author. “They have the potential to be processed at industrial-scale quantities and at low cost compared to other materials.”
Use the leftovers
Biomaterials manufacturing could be a natural extension of the paper and biofuels industries, using technology that is already well-established for cellulose-based materials.
“Some of the byproducts of the paper industry now go to making biofuels, so we could just add another process to use the leftover cellulose to make a composite material,” Moon says. “The cellulose crystals are more difficult to break down into sugars to make liquid fuel. So let’s make a product out of it, building on the existing infrastructure of the pulp and paper industry.”
Their surface can be chemically modified to achieve different surface properties.
“For example, you might want to modify the surface so that it binds strongly with a reinforcing polymer to make a new type of tough composite material, or you might want to change the chemical characteristics so that it behaves differently with its environment,” Moon adds.
Zavattieri plans to extend his research to study the properties of alpha-chitin, a material from the shells of organisms including lobsters, crabs, mollusks, and insects. Alpha-chitin appears to have similar mechanical properties as cellulose.
“This material is also abundant, renewable, and waste of the food industry,” he says.
The Forest Products Laboratory through the US Department of Agriculture, the Purdue Research Foundation, and the National Science Foundation funded the research.
Source: Purdue University