Polyester Blend Aids In Scientific Pursuit Of Future Composites

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 fabricof fibers, such as glass or carbon, and then injecting thosepre-formed structures with plastic resins, or by molding apre-mixed paste of resin and fibers. The reinforcing fibersimpart greater strength to the composite parts. But the processis complicated, expensive and labor intensive.

Therefore, materials scientists have been trying to makeso-called "molecular composites" that naturally contain built-infibers. The result would be a sort of self-assembled compositethat could be injected into molds, eliminating steps now neededto incorporate fibers separately. Although the idea for molecularcomposites--a flexible polymer reinforced by a rigid polymer--wasfirst conceived more than 20 years ago by late Nobel laureatePaul J. Flory, scientists only recently have been able to producethem.

NIST researchers achieved such a composite and have learned howthe reinforcing fibers form. This work was presented today in aposter paper in New York, during this year's Annual TechnicalConference of the Society of Plastics Engineers. The paper waswritten by Fang Qiao, Kalman Migler and Charles C. Han,scientists in the Polymers Division of the NIST Materials Scienceand Engineering Laboratory.

The researchers have developed a process in which polyester isdramatically strengthened with a material known as a liquidcrystalline polymer. The liquid crystalline polymer used in theresearch is called Vectra , a plastic material similar to Kevlarthat is five times stronger than steel. By combining the polymerand polyester at just the right mixing speed and temperature, theVectra forms fibrils that are embedded in the polyester andattached to the polyester molecules. That attachment is essentialfor reinforcement and is enhanced by adding epoxy, which acts asa coupler between the polyester and the liquid crystallinepolymer molecules.

Polyester is used because its chemical structure is ideal formaking bonds with the liquid crystalline polymer. Theresearchers, who have been working on the process for a year anda half, also developed a system that uses a light-scatteringdetector and video microscopy to analyze the composite materialas it is being produced, allowing critical adjustments to be madein chemistry, temperature, composition and mixing speed in realtime.

So far, the research has shown that the strength of polyester ismore than doubled in a composite containing only 0.2 percent ofVectra . At around $8 a pound, Vectra is far more expensive thanpolyester, which costs less than $1 a pound. For that reason, theaim is to use as little liquid crystalline polymer as necessaryto produce composites with the necessary strengths and otherproperties.

The NIST research is ongoing. Future work will include researchwith mixtures that contain higher concentrations of Vectra , orother types of liquid crystalline polymers, yielding evenstronger polyester materials.

As a non-regulatory agency of the U.S. Department of Commerce'sTechnology Administration, NIST promotes economic growth byworking with industry to develop and apply technology,measurements and standards through four partnerships: theMeasurement and Standards Laboratories, the Advanced TechnologyProgram, the Manufacturing Extension Partnership and the BaldrigeNational Quality Program.