Cellulose nanocrystals
possible 'green' wonder material
WEST LAFAYETTE, Ind. - The same tiny cellulose crystals
that give trees and plants their high strength, light weight and resilience,
have now been shown to have the stiffness of steel.
The nanocrystals might be used to create a new class of
biomaterials with wide-ranging applications, such as strengthening construction
materials and automotive components.
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, said Pablo D.
Zavattieri, a Purdue
University assistant professor of civil engineering.
This is a material that is showing really amazing
properties," he said. "It is abundant, renewable and produced as
waste in the paper industry."
Findings are detailed in a research paper featured on the
cover of the December issue of the journal Cellulose.
"It is very difficult to measure the properties of
these crystals experimentally because they are really tiny," Zavattieri
said. "For the first time, we predicted their properties using quantum
mechanics."
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 paper was authored by Purdue doctoral student Fernando
L. Dri; Louis G. Hector Jr., a researcher from the Chemical Sciences and
Materials Systems Laboratory at General Motors Research and Development Center;
Robert J. Moon,
a researcher from the U.S. Forest Service's Forest Products Laboratory; and Zavattieri.
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 said. "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. Applications for biomaterials made from the cellulose nanocrystals
might include 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," Moon said. "They have the
potential to be processed at industrial-scale quantities and at low cost
compared to other materials."
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 said. "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 said.
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 said.
The research was funded by the Forest Products Laboratory
through the U.S. Department of Agriculture, the Purdue Research Foundation and
the National Science Foundation.
http://www.purdue.edu/newsroom/releases/2013/Q4/cellulose-nanocrystals-possible-green-wonder-material.html
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