| "These results are quite significant. In particular, it's really hard to reduce water permeation." Professor John Booske |
Go to any grocery store and you'll find freezers, coolers and shelves stocked with products that benefit from special packaging. Items ranging from meat to cheese to potato chips rely on protective oxygen and water, prolonging their shelf life. In many cases, these protective materials are also transparent, allowing consumers to closely inspect the food prior to making a purchase.
While the ability to "preview" edibles before buying them is beneficial, there is a downside to transparent polymer wraps: See-through polymeric materials have more space between their molecules and therefore are not nearly as effective as opaque wraps that rely on a thin metallic layer to keep out detrimental elements. This is a dilemma for companies such as Curwood Inc., of Oshkosh, an industry leader in developing and producing high-performance, high-barrier, polymer-based packaging materials.
Researchers at Curwood, Inc., strive to improve high-performance, high-barrier, polymer packaging materials. These materials are used to protect many of the food products found in grocery stores. |
To help solve this problem, Curwood drew on the resources of the Wisconsin Plasma Processing and Technology Research Consortium, of which it has been a member for many years. Plasma-aided manufacturing involves using partially ionized gases to alter surfaces, produce new or improved materials, and develop new chemical compounds and processes. Under the direction of Professor John H. Booske -- and with the aid of a three-year Industrial & Economic Development Research grant from University-Industry Relations (a technology transfer arm of the graduate school) -- a team of scientists, students and faculty colleagues began looking for plasma surface modification techniques that would offer the same oxygen and water resistance as thin metallic films while retaining transparent qualities.
"The process began with discussions on what constitutes a successful barrier," says Kevin Nelson, Curwood's materials development manager. Once the College of Engineering team had a better idea of what was needed in industry, it began experimenting with different materials and processes. Curwood then analyzed the treated materials and films for permeation resistance.
"By making a plasma discharge in a rich chemical soup, you can engineer a whole range of end products into your film that eventually enhance the properties or performance of your substrate," explains Booske. For example, during the first year of the study, efforts focused on using plasma source ion implantation (a process developed by UW-Madison Professor John R. Conrad -- silver.neep.wisc.edu/psii) to oxidize just the top half of an aluminum thin film, which left it reasonably transparent, says Booske. "However, the resulting film was more vulnerable to cracking when flexed than the original concept had predicted." Researchers also tried depositing a variety of chemical compounds as polymeric thin films, but these methods fell short of Curwood's transparency diffusion standards.
In the final year of the study, the plasma engineering team developed a methane-based process that showed the best results reported to date -- reducing water permeation by a factor of four and oxygen permeation by a factor of 120. The resulting treated material has a slight darkening in color but still retains transparency. "These results are quite significant," says Booske. "In particular, it's really hard to reduce water permeation."
The findings, which have been demonstrated in the laboratory, are quite promising, says Curwood's Nelson. However, he notes, the development process still has a ways to go. "It's one thing to demonstrate these properties in a static situation, it's another to bring them into full-scale operation." But Nelson says he's optimistic that this breakthrough could one day be put to use on the manufacturing floor. "The trend is in the right direction. We just need to push it further."
To scale things up to Curwood's needs would require demonstrating a configuration that would achieve the same results with a continuous flow process, says Booske. "This means Curwood would need either new equipment or modifications to existing equipment. But the fact that it's been demonstrated to be able to do these types of processes at the rate needed was a final factor in getting Curwood to acknowledge this solution has commercial potential."
One tool that could help in transferring this technology to industry is a prototype continuous-flow system developed and patented by a College of Engineering scientist. "This apparatus will help with the scale-up process," says Nelson. A couple of equipment manufacturers have expressed an interest in producing this patented equipment.
"This has been a nice collaborative effort," says Nelson, looking back on the three-year study. And, he notes, the partnership will continue through his company's membership in the Wisconsin Plasma Processing and Technology Research Consortium. "We've come a long way, and now we need to push the technology even further."
--By Paul Bauman--
| For further information, please contact: |
John H. Booske, 608/262-8548
booske@engr.wisc.edu
Copyright 1999 The Board of Regents of the University of Wisconsin System
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Date last modified: Wednesday, 03-Mar-1999 12:00:00 CST
Date created: 03-Mar-1999
