Scientists at the Commerce Department’s National Institute of Standards and Technology today announced that they have taken a major step toward the manufacture of strong yet inexpensive composite materials, developing a more efficient production method than those currently in use.
Today’s molded composite parts are used in everything from cars, boats and aircraft to sporting goods and other consumer products. They are made by first fashioning skeletons out of a woven fabric of fibers, such as glass or carbon, and then injecting those pre-formed structures with plastic resins, or by molding a pre-mixed paste of resin and fibers. The reinforcing fibers impart greater strength to the composite parts. But the process is complicated, expensive and labor intensive.
Therefore, materials scientists have been trying to make so-called "molecular composites" that naturally contain built-in fibers. The result would be a sort of self-assembled composite that could be injected into molds, eliminating steps now needed to incorporate fibers separately. Although the idea for molecular composites—a flexible polymer reinforced by a rigid polymer—was first conceived more than 20 years ago by late Nobel laureate Paul J. Flory, scientists only recently have been able to produce them.
NIST researchers achieved such a composite and have learned how the reinforcing fibers form. This work was presented today in a poster paper in New York, during this year’s Annual Technical Conference of the Society of Plastics Engineers. The paper was written by Fang Qiao, Kalman Migler and Charles C. Han, scientists in the Polymers Division of the NIST Materials Science and Engineering Laboratory.
The researchers have developed a process in which polyester is dramatically strengthened with a material known as a liquid crystalline polymer. The liquid crystalline polymer used in the research is called Vectra™, a plastic material similar to Kevlar™ that is five times stronger than steel. By combining the polymer and polyester at just the right mixing speed and temperature, the Vectra™ forms fibrils that are embedded in the polyester and attached to the polyester molecules. That attachment is essential for reinforcement and is enhanced by adding epoxy, which acts as a coupler between the polyester and the liquid crystalline polymer molecules.
Polyester is used because its chemical structure is ideal for making bonds with the liquid crystalline polymer. The researchers, who have been working on the process for a year and a half, also developed a system that uses a light-scattering detector and video microscopy to analyze the composite material as it is being produced, allowing critical adjustments to be made in chemistry, temperature, composition and mixing speed in real time.
So far, the research has shown that the strength of polyester is more than doubled in a composite containing only 0.2 percent of Vectra™. At around $8 a pound, Vectra™ is far more expensive than polyester, which costs less than $1 a pound. For that reason, the aim is to use as little liquid crystalline polymer as necessary to produce composites with the necessary strengths and other properties.
The NIST research is ongoing. Future work will include research with mixtures that contain higher concentrations of Vectra™, or other types of liquid crystalline polymers, yielding even stronger polyester materials.
As a non-regulatory agency of the U.S. Department of Commerce's Technology Administration, NIST promotes economic growth by working with industry to develop and apply technology, measurements and standards through four partnerships: the Measurement and Standards Laboratories, the Advanced Technology Program, the Manufacturing Extension Partnership and the Baldrige National Quality Program.
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