By Steve Karsjen
On this day there are six large white boxes stacked neatly along the wall of Roger Jones' laboratory. The boxes each contain several bags of wood chips from Douglas Fir trees. Each of the chips ranges in size from approximately an inch to an inch and a half long to about an inch wide.
Altogether there are thousands, perhaps hundreds of thousands of wood chips in the boxes, which have been shipped to Jones by the Weyerhaeuser Paper Company, an industry giant in the making of paper and paper products. Weyerhaeuser has supplied the wood chips as part of a three-year research project in which Ames Laboratory scientists are participating to improve paper-industry techniques for analyzing the major components of timber harvested from forests across America.
The Ames Lab research revolves around the use of Transient Infrared Spectroscopy, or TIRS, which was invented by Jones, an Ames Laboratory associate chemist, and Ames Lab physicist John McClelland. TIRS relies on spectroscopy, the art of analyzing substances by measuring the radiant (light or heat) energy their molecules either emit or absorb and then interpreting the resulting electromagnetic spectra.
Today manufacturers are most interested in the mid-infrared (mid-IR) portion of the spectrum (400 to 4000 cm-1), which contains an abundance of information about a material's molecular and chemical makeup. But solids, like wood chips, aren't popular in the mid-IR because they are thick and absorb infrared radiation. So in order to perform spectroscopic analysis of wood chips or other materials in the mid-IR region, technicians are forced to remove samples of the materials randomly from the process line, prepare thin or diluted specimens from the samples and then conduct the spectroscopic analysis in the laboratory.
Thin samples are necessary to obtain useful spectra for analysis. If it sounds like a labor intensive, lengthy, and costly process -- one that slows down the type of quality control necessary in the paper-making process -- it is. "Of course, anytime you have to go off-line and into the laboratory, the measurement process becomes much slower and more expensive," Jones says.
Whereas current technology is slow and cumbersome, the TIRS technique is fast and efficient, providing on-line analysis. TIRS actually takes advantage of the fact that the material, whatever it is, is moving down the process line. "The material has to be moving in order for TIRS to work," says McClelland.
TIRS can't actually make a thick material thin, but it can trick the infrared spectrometer into thinking that's the case. To do so, Jones reduces absorption by inducing a temperature transient in the moving surface of the wood chips as they move by on their way to the digestor that feeds into the paper machine. Gas jets blowing on the material temporarily create a very thin hot or cold layer at the surface of the material without physically thinning it. The mid-IR spectrum of the thin layer can then be measured by an infrared spectrometer.
With a laboratory model of a wood chip process line, Jones demonstrates the TIRS technique by placing wood chips on a large circular plate, which looks a lot like an oversized pizza pan. The chips are piled up along the outer edge of the plate and rotate with it as the plate spins around and around. At one point in the rotation, the chips come in contact with a hot blast of air from a gas jet, which strikes the surface of the chips, heating them. As the wood chips rotate through the field of view of an infrared spectrometer, the spectrometer measures the electromagnetic spectra of the heated sample.
In Jones' experiment, the spectra being measured come from one of the major components of wood, lignin, the material that turns paper brittle and yellow over time. Low quality paper, like newsprint, contains a lot of lignin while most of the lignin is removed from high-quality paper. "By keeping track of how much lignin the wood contains, technicians control the quality of the paper they're producing," says Jones.
In addition to its on-line capabilities, TIRS conducts its analysis in real-time. "This is actually the most important aspect of TIRS," says McClelland. "Real-time measurement allows you to get data immediately so you can make adjustments that improve the quality of the paper on-line."
Jones had a pretty good idea TIRS would provide the type of analysis the paper industry needs. Since its invention, the TIRS technology has been successfully used to analyze over a hundred materials from plastics to coal and corn. All of these samples were smooth, however, which is a far cry from the rough, irregular-shaped wood chip samples provided by the paper industry. There was also a question of whether the TIRS technology would work across tree species (hardwoods and softwoods) and on trees from all regions of the country.
"Our model contains over a dozen species at this time," says Jones. "So far they haven't thrown anything at us that we haven't been able to analyze."
Although Jones says initial feedback from the paper industry on TIRS has been "good," he'll have a better feel for whether it will be effective when an actual field test is conducted. Other analysis techniques are also being considered by the paper industry at this time, which, McClelland admits, may actually prove to be better fits than TIRS.
"If that's the case, then there may be additional aspects of the paper-making process that can benefit from the TIRS technology," says a confident McClelland, who adds that instead of using TIRS to analyze wood chips as they are going into the paper digestor, it might be better to conduct the TIRS analysis at the other end of the production process, where the paper is being manufactured by the paper machine.
"We're already conducting tests on different paper coatings and paper processes to see how well our technique works," says McClelland.
And beyond the paper manufacturing-industry, McClelland and Jones are looking at adapting TIRS to meet specific needs of the glass industry.
"We have a proposal to analyze the 'cure' of coatings on fiber optic cables," says McClelland. If not properly cured, the cables stick together and the coatings tear as the cables are being unwound from spools. This amounts to a multi-million dollar problem for this industry and we hope there might be an opportunity for TIRS to also have some impact in this area."
For more information:
Roger Jones, (515) 294-3894, jonesrw@ameslab.gov
John McClelland, (515) 294-7948, mcclelland@ameslab.gov
Current research funded by:
DOE Energy Efficiency and Renewable Energy Office
Last revision: 12/17/99 sd
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