NIST Researchers Create Molecular Composite Materials

Scientists at the Commerce Department's National Institute of Standards and Technology (NIST; Gaithersburg, MD; 301-975-NIST) have developed a more efficient method for producing composite materials. The results of this new process, so-called "molecular composites," represent a major step toward the manufacture of strong yet inexpensive composite materials. These composites would have a variety of potential applications, from cars, boats, and aircraft to sporting goods and other consumer products.

Molded Composites Vs. Molecular Composites
Creating Molecular Composites
Finding The Right Mixture

Molded Composites Vs. Molecular Composites (Back to Top)
Today's molded composite parts 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. Unfortunately, the current process is complicated, expensive, and labor intensive.

For years materials scientists have been trying to fashion 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.

Creating Molecular Composites (Back to Top)
After a year and a half of work, NIST researchers have developed a process in which polyester is dramatically strengthened with a material known as a liquid crystalline polymer. In this study, the researchers a liquid crystalline polymer called Vectra, a plastic material similar to Kevlar. 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 's chemical structure is ideal for making bonds with the liquid crystalline polymer. The researchers 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.

The work was presented in a poster paper at the Annual Technical Conference of the Society of Plastics Engineers in New York. 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.

Finding The Right Mixture (Back to Top)
The research has shown that the strength of polyester is more than doubled in a composite containing only 0.2% of Vectra. At around $8 a pound, Vectra is far more expensive than polyester, which costs less than $1 a pound. The aim is to use as little liquid crystalline polymer as necessary to produce composites with the necessary strengths and other properties. In future work, the researchers will focus on mixtures that contain higher concentrations of Vectra, or other types of liquid crystalline polymers, yielding even stronger polyester materials.

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.

For more information, call Fang Qiao at 301-975-4295, or e-mail fang.qiao@nist.gov.