Purdue News

January 21, 1991

Prof. Turns Corn, Waste Paper Into Rayon

West Lafayette, Ind. -- A new chemical process that makes an extremely strong silk-like fiber from sources as varied as corn and wheat stalks, straw, and wood pulp could be used to make a tough new rayon cloth, according to Purdue University Professor Li Fu Chen.

The process, which was recently patented by Chen, 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," Chen says.

Cellulose is a chain of sugar molecules that makes up such common products as wood and paper. Rayon 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.

Rayon is fiber that produces a cloth that has a texture similar to raw silk. It is used in tire cords and industrial products as well as clothing.

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.

Chen says that developing the process was a personal triumph as well as a scientific one: "Fifteen years ago at a scientific meeting everyone said that this (chemical process) couldn't be done," Chen says. "But we stayed with the research and after 15 years we've been able to make the process work." Chen presented a paper on his process at the 1990 national meeting of the American Chemical Society.

Chen's process has several advantages over the standard ways of producing fiber from cellulose:

*It can use cellulose from any source. Currently, 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. "If you have a cotton or rayon shirt, and nobody likes that color, just throw it into the solution, manufacture new fiber, and make a new shirt," he says, adding, "We've actually done this and it works well."

*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 so that it can be recycled. "The reason rayon is so expensive to manufacture today is because of all of the pollution controls and because the chemicals cause the equipment to corrode quickly," Chen notes.

*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.

A manufacturer in Tennessee has begun testing the procedure to determine if it can be used on an industrial scale. If the tests are successful, Chen says, the low-cost rayon could make its way to consumers within five years.

If the process proves successful on an industrial level, 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.

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, according to Chen.

Purdue News Service: (765) 494-2096; purduenews@purdue.edu