Magnetic resonance imaging (MRI) has significantly enhanced diagnostic medicine by allowing physicians to look deep inside the human body without using a scalpel.
Now, researchers at the Georgia Institute of Technology are applying the technique to a broad range of industrial processes, using MRI to watch carpet dry from the inside, peer into peanut shells, and study how fabrics wick moisture away from the body. The work could lead to faster and more efficient drying processes, carpet less prone to mildew, and fabrics that are more comfortable to wear.
"The advantages for us are the same as for the medical community," explained Dr. Haskell W. Beckham, associate professor in Georgia Tech's School of Textile and Fiber Engineering. "The technique is non-invasive; we don't need special tracers, dyes or contrast agents for image capture, and information can be extracted from arbitrary locations inside opaque objects."
The Georgia Tech researchers are believed to be the only ones in the world using MRI to study textile drying.
Using the instrumentation in Georgia Tech's Nuclear Magnetic Resonance Center, Beckham and his collaborators have examined how moisture flows into carpets, measured where it accumulates, and monitored its removal as a function of time during conditions simulating industrial drying processes. They've also seen how surface fluorocarbon finishes affect the way water penetrates into the carpet.
While such information on fluid behavior within textiles is important in itself, it also provides a means for describing the internal structure of the material. This is especially useful for soft porous substrates such as textiles; the traditional method required physically cutting the sample into thin slices and then examining each slice using microscopy. Soft materials are easily deformed during such sample preparations.
The MRI technique has the unique ability to follow fluid distribution in real time. "For carpets and textiles, you can't get this information any other way," he said. "Simply stated, all we do is wet the sample, put it in the instrument, and take snapshot images as a function of drying time."
Beckham will present the latest MRI results at the 218th National Meeting of the American Chemical Society in New Orleans, LA. His collaborators in the work are Dr. Wallace W. Carr and Dr. Johannes Leisen of Georgia Tech, and Dr. Hubert Kinser of Dalton College. The presentation, GEOC 63, will take place at 3:25 p.m. August 25, 1999.
Magnetic resonance imaging uses powerful magnetic fields to align the magnetic moments of the nuclei in molecules. Following an excitation pulse of electromagnetic radiation, the nuclei return to their original state and give off a signal that can be measured and analyzed, showing scientists where the molecules are located.
The Georgia Tech MRI instrument is much smaller than a hospital machine designed for imaging the human body. Beckham and his collaborators study a sample about one inch in diameter, imaging it repeatedly to see how moisture levels change over time as they apply heated air.
The carpet imaging has provided a few surprises. For example, it was found that moisture can flow into cut-pile carpet through the center of its tufts, even when the carpet contains a fluorochemical finish. The water then concentrates near the carpet backing, even if the carpet sample is placed upside-down in the machine.
This information is important to manufacturers because drying carpet after dyeing and finishing steps slows the manufacturing process and consumes large amounts of energy. By knowing the drying rates at different locations within the carpet, researchers could improve the drying process. One possibility being considered is the addition of an infrared predryer to concentrate energy onto the carpet backing, where the moisture is concentrated.
"The drying process is the limiting factor in the speed of the carpet production process," Beckham explained. "If we can improve the efficiency of the drying process, we can dry more quickly and the manufacturer will be able to produce more carpet in less time. And if we can dry carpet with less energy, that's ultimately good for the environment."
The benefits could also extend to property owners in humid climates where mildew can be a problem. By understanding how water enters and leaves carpet, the researchers may be able to help manufacturers design a carpet structure and coating system less prone to trap moisture.
That project, supported by the Consortium for Competitiveness in the Apparel, Carpet and Textile Industries (CCACTI), also involves microbiologists at the University of Georgia.
"There are different ways to make carpet," Beckham said. "We're looking at the different constructions and treatment combinations to see if one is less favorable for supporting microorganism growth. This could be a major issue for the carpet industry in south Florida and south Texas where the humidity is very high."
Moisture flow in textiles is also important for those who value fabrics that draw sweat away from the body as they exercise. In a relatively new program, Beckham will use MRI to examine how different fabrics and fabric structures wick moisture away from the skin.
For food processors, the researchers have also looked at moisture and oil concentrations in peanut shells. Like textiles, peanuts must be dried during processing, and that consumes energy. To determine where the moisture and oil concentrate, the researchers used a selective MRI imaging sequence.
"In the normal imaging sequence, we can place a series of excitation pulses that act as a filter to differentiate oil from moisture," Beckham explained. "As long as there is a chemical difference between fluids, we can use a filter to select for one of them. This fluid-selective imaging capability is another special distinction of MRI as compared to other imaging methods."
Beyond carpet, apparel and peanuts, the researchers are using MRI to study how moisture enters fertilizer pellets, where moisture concentrates in fiber-reinforced composites, and even how chemically different fluids mix while flowing.
"We see tremendous potential for the application of magnetic resonance imaging to a variety of engineering challenges," he said. "This is a very powerful technique that has been extensively developed and used in the medical community, while its application in materials science or engineering is not yet as common."
The work has been sponsored by the National Science Foundation, the National Textile Center, and the Georgia Consortium for Competitiveness in the Apparel, Carpet and Textile Industries (CCACTI).
Technical Contact: Dr. Haskell Beckham (404-894-4198);
E-mail: haskell.beckham@textiles.gatec
h.edu.