COLUMBUS, Ohio -- Researchers at Ohio State University have found a way
to make synthetic cloth fibers softer and more absorbent.
The technique may one day boost the absorbency of diapers and feminine hygiene
products, and make these items stronger, lighter, and less bulky. It may
also lead to softer facial tissues.
David Tomasko, assistant professor of chemical engineering at Ohio State,
and his colleagues found that a supercritical fluid form of carbon dioxide
could deposit a chemical additive into a sheet of polymer fibers to make
the material more absorbent. The research appeared in a recent issue of
the journal Industrial & Engineering Chemistry Research.
Supercritical carbon dioxide is composed of carbon dioxide molecules heated
under pressure and held in a state somewhere between a liquid and a gas.
"If you could put supercritical carbon dioxide in a box and look at
it, it would look like a gas," said Tomasko. "It flows very easily,
and penetrates things very easily. You don't typically think of gases as
being able to dissolve things, but they do, and supercritical fluids dissolve
things even better."
The supercritical carbon dioxide carries additives deep into materials like
cloth, plastic, and paper, just as hazardous organic solvents do, but without
diminishing the material's appearance or strength, and without creating
hazardous chemical byproducts.
In the study, the researchers drove supercritical carbon dioxide into a
polymer, a material in which the stringy molecules wrap around each other
like a tangled rope. The carbon dioxide molecules wedged between the strings,
swelling the polymer matrix. Tomasko and his colleagues found that once
the polymer swelled, other molecules could enter the polymer much more easily
through the enlarged holes between the strings.
In this case, the researchers added molecules of detergent to the swollen
polymer to make it absorb water better. After they removed the supercritical
carbon dioxide and the polymer shrunk back down to its original size, the
detergent molecules remained trapped inside the polymer.
"We didn't change the chemical nature of the polymer, and we didn't
change its strength," said Tomasko. "We changed the surface properties
by adding the detergent. Now, instead of beading up on the surface of the
polymer, water molecules spread out and wet the surface."
In the future, this technique could make polymer fibers pick up moisture
faster and more easily in diapers and feminine hygiene products. A polymer
treated with detergent and supercritical carbon dioxide is stronger, lighter,
and less bulky than cellulose, the traditional absorbent material in these
products. A different type of additive could make facial tissues softer.
Supercritical carbon dioxide appears to deposit additives in these materials
better than liquid solvents such as water. Such liquid solvents don't let
the polymer strings shrink back into their original shape. They can kink
up the material and make it weak.
"A really good example of the effects of liquid solvent on a material
is what happens when you get a piece of paper wet. Water penetrates the
fibers of the paper, so the paper swells a little bit. And when the water
evaporates out of the paper it pulls those fibers and twists them, so the
paper crinkles. A supercritical fluid wouldn't do that," said Tomasko.
Now Tomasko wants to find out how fast the process works. He and the other
researchers are constructing a device that will contain the polymer at high
pressure and time how long it takes for the supercritical carbon dioxide
and additive to penetrate the material.
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Contact: David Tomasko, (614) 292-4249; Tomasko.1@osu.edu
Written by Pam Frost, (614) 292-9475; Frost.18@osu.edu