Page 63 - Plastcs News August 2017

TEChNOLOGY

New Method to improve New technique to make heat

properties of polymers pass through plastic

esearchers at the Department of Energy have esearchers in materials science and mechanical
Rdiscovered a surprising way to improve the properties Rengineering at the University of Michigan (UM)
of polymers by blending nanoparticles with polymer have developed a new technique that can change
materials. A team of scientists led by the DoE’s oak Ridge plastic's molecular structure to help it cast off heat.
National Laboratory (oRNL) were studying the role of The new technique uses a process that engineers the
polymer structure, the interaction between nanoparticles
structure of the material itself, considering the nature
of plastics made of long chains of molecules that are
tightly coiled and tangled like a bowl of spaghetti,
Xinhua reported.

It used a chemical process to expand and straighten
the molecule chains, giving heat energy a more direct
route through the material. To accomplish this, the
researchers first dissolved a typical polymer, or plastic
in water, then added electrolytes to the solution to
raise its pH, making it alkaline. The individual links
in the polymer chain, called monomers, take on a
and polymer, and nanoparticle size and shape on the negative charge, which causes them to repel each
structure, dynamics, and macroscopic properties of other. As the monomers spread apart, they unfurl the
polymer nanocomposites, which are used in numerous chain's tight coils. Finally, water and polymer solution
applications.Understanding these effects would allow is sprayed onto plates using a common industrial
the team—which also included researchers from the process called spin casting, which reconstitutes it
University of Illinois at Urbana-Champaign (Illinois) and into a solid plastic film. The uncoiled molecule chains
the University of Tennessee, Knoxville (UTK) - to improve
the design of new composite polymers, since they can within the plastic make it easier for heat to travel
tune mechanical, chemical, electrical, optical and thermal through it.Researchers also found that the process
properties. In particular, the team was trying to verify that has a secondary benefit: it stiffens the polymer
shrinking the nanoparticle size would adversely affect the chains and helps them pack together more tightly,
mechanical properties of polymer nanocomposites, but making them even more thermally conductive.
they learned something else entirely, according to Alexei "Polymer molecules conduct heat by vibrating, and a
Sokolov, a researcher from ORNL and UTK. “We expected stiffer molecule chain can vibrate more easily," said
that there is a limit of how small a nanoparticle should be Apoorv Shanker, a materials science and engineering
to affect macroscopic properties of nanocomposite. And graduate student."Think of a tightly stretched guitar
at the nanoparticle size, we expected either no effect string compared to a loosely coiled piece of twine.
or deterioration of nanocomposite properties. We got a
surprise.” The guitar string will vibrate when plucked, the twine
won't. Polymer molecule chains behave in a similar
What researchers learned instead was not that an optimal way," Shanker added. The process is a major departure
nanoparticle size must exist, which is what they believed from previous approaches, which have focused
they would discover. Instead, they found that moving to on adding metallic or ceramic fillers to plastics, a
really small nanoparticles enabled them to access totally
new properties, Sokolov said. This occurred not due to process that is expensive as well as can change the
size but because small particles move faster than large properties of the plastic in undesirable ways.The work
ones and interact with fewer polymer segments on the has important consequences because of the large
same chain. Many more polymer segments stick to a large number of polymer applications where temperature
nanoparticle, making dissociation of a chain from that is important. The study has been published in the
nanoparticle difficult. journal Science Advances.

63 Aug ust 2017 | Plastics News