Purdue News

March 19, 1993 Professor turns waste paper into silk-like cloth You may not be able to make a silk purse from a sow's ear, but a Purdue University professor has figured out how to make silk-like rayon from recycled office paper–a material that is more readily available than pig's protuberances, anyway. The chemical process can also make cloth from corn and wheat stalks, straw, and wood pulp, and an Indiana company is hoping to use the technique to make high-quality home insulation from recycled newspapers. The Purdue-developed process uses a relatively safe chemical, zinc chloride, to make fiber from low-grade cellulose. "For the first time we can make fiber from almost any source of cellulose, even from waste paper from offices," says Li Fu Chen, associate professor of food science. "We're hopeful that we've found uses for a waste product that had no value," says Philip Nelson, head of Purdue's Department of Food Science. "The term 'value-added' certainly applies to this research project." Three companies are examining the process to determine if it will be practical for their operations: Regal Industries of Crothersville, Ind., is looking at the process to improve cellulose insulation for home building construction. The company currently makes blow-in cellulose insulation from recycled newspapers, but says it hopes to use fibers spun using the new process to improve blow-in insulation, and to make bats of cellulose insulation from the process. "Insulation 'batts' are the most popular form of insulation because of the way most buildings and homes are built today, and nearly all of those are made with fiberglass or rock wool," says Duvon McGuire, director of research at Regal Industries. "But one advantage of cellulose insulation is that it doesn't have convective loops that you have with fiberglass." The result, McGuire says, is that insulation made using cellulose normally has a higher "R value" than comparable fiberglass insulation, which means that it provides more insulation per inch of thickness. North American Rayon of Elizabethton, Tenn., says it hopes to use the process to produce rayon yarn, and has donated equipment and technical assistance to Chen's laboratory. If the research on the yarn is successful, Chen says, the low-cost biodegradable rayon could make its way to consumers within five years. A Japanese company is also looking at the process hoping to manufacture rayon. Cellulose is a chain of sugar molecules that makes up such common products as wood and paper. Rayon, a fiber that produces a cloth that has a texture similar to raw silk, is formed by separating out the chains and forming them into fibers. Before Chen's process was developed, rayon could only be made from high-quality cellulose made up of very long chains. Although the method of using zinc chloride to extract fiber from cellulose was discovered in 1889, the fibers produced weren't strong enough to use. According to Chen, his process produces a fiber that is several times stronger than present-day rayon. "We are now looking at how the purity of the chemical and biomass [cellulose raw material] affect the purity of the cloth fibers," Chen said. "We are also trying to find the ideal mix of chemicals in the process. The fiber strength can vary two to three times depending on the mixture we use." Chen's process has several advantages over the current methods of producing fiber from cellulose: It can use cellulose from any source. Presently, only high-quality wood pulp can be used to make rayon, but Chen says that with his-process rayon could be made from virtually any grade pulp –including that made from recycled paper or agricultural by-products such as corn stalks. It would even be possible to dissolve materials made from the fiber and recover cellulose from them, according to Chen. The process doesn't harm the environment. one of the chief problems associated with rayon is that the viscose manufacturing process (the most common method) uses toxic chemicals. The zinc chloride is a much safer chemical, and it can be recovered from the manufacturing process and recycled. The process used to make the fiber is much faster and cheaper than the methods now used. Chen's method allows almost instantaneous production of fiber; current methods can take up to 18 hours. Also, because the process can use almost any pulp source, the raw materials are much cheaper. The method produces a fiber that is free of chemical residue. This would allow the fiber to be used for food packaging or in medical procedures. Chen says he foresees the fibers being used to make an inexpensive form of graphite, or carbon-fiber, material. This material, known for its strength and light weight, is currently used to make products as diverse as tennis rackets and military fighter-airplane parts. If the material could be made cheaply, it would be an ideal material for auto parts, Chen says. "It's farfetched, but an entire automobile could be made so that it is biodegradable," Chen says. Because cellulose is just one component of plant tissue, or biomass, Chen is now at work on using other components found in the raw materials. Agricultural biomass, for example, could be used as food for farm livestock, and lignin, which is the substance that makes plant cells rigid, could be converted into a hard, plastic-like material, or used as an adhesive. "Finding uses for lignin is the third generation of biomass conversion," Chen says. "Plant tissue is one-third hemicellulose, one-third cellulose, and one-third lignin. Making ethanol from the hemicellulose was the first generation of biomass conversion. The second was making materials, such as our rayon, from the cellulose. The next step will be to use the lignin." Chen is working with Purdue's Wood Research Laboratory to use lignin as an adhesive in composite lumber products such as plywood. The current adhesive, phenolic formaldehyde, is made from petroleum and is a toxic material. Lignin would have the advantage of being much more environmentally safe since it is a naturally occurring poly-phenolic thermoplastic. Lignin is most often found in industry as a waste product from the manufacturing of paper. Chen and Nelson both say it is not unusual that a food scientist is developing building materials and cloth from agricultural waste products, since Chen uses the same techniques and tools for his research that are used by other food scientists. Chen says his research is important to the future of agriculture in Indiana and the United States. "Today, agriculture is based on the production of food," Chen says. "But as we find other uses for agricultural products, we will have a world of other markets. In the future, agriculture–not manufacturing–will again be the basis for the world economy." NOTE: A black-and-white photograph is available. Contact Purdue News Service (765) 494-2096 or purduenews@purdue.edu To the Purdue News and Photos Page