Relaxation Behavior and Optical Transmission of Nylon/Clay Nanocomposites

Monitored During Compounding by an Online Dielectric Sensor

Yu-Hsin Lee, Anthony J. Bur, Steven C. Roth and Paul Start

MSEL, Polymers Division

Polymer/clay nanocomposites are industrially important materials because a small amount of clay filler (less than 5 % by weight) mixed with the polymer resin produces vastly improved mechanical and thermal properties compared to the unfilled polymer. A key factor that controls the properties of the compounded product is the extent of exfoliation and intercalation of the clay particles in the polymer matrix. Exfoliation is the process of reducing micron size clay particles to nano size silicate flakes and dispersing the flakes throughout the resin matrix. Analyzing and quantifying the amount of exfoliation of a compounded product usually involves extensive post processing examination using X-ray and transmission electron microscope (TEM) observations. The objective of this project is the application of dielectric and optical instrumentation to monitor the microstructure of the composite during processing, thus eliminating time consuming off-line measurements. We will present real-time measurements during compounding of nylon 11 with organo-modified clays using an innovative dielectric slit die sensor that was attached to a twin screw extruder. The organic modification of the clays involves an ion exchange of Na+ ions in the gallery regions between silicate layers of the natural clay with alkyl ammonium ions that render the clays more compatible with organic resins. Several organo-modified clays are used in this study to produce nanocomposites with varying amounts of exfoliation. On-line dielectric and optical transmission data are correlated with off-line X-ray and TEM observations to establish relationships between on-line and off-line determinations of the extent of exfoliation. The dielectric data display a Maxwell-Wagner relaxation whose characteristic frequency is a function clay microstructure where the characteristic frequency decreases with the extent of exfoliation. The on-line optical transmission data also correlate with the extent of exfoliation where optical transmission increases with the exfoliation because the exfoliated nano particles are too small to scatter light. Using the optical transmission and Maxwell-Wagner characteristic frequency, we establish an exfoliation scale that can be used to quantify the extent of exfoliation.

Yu-Hsin Mandy Lee

Polymers Division, Materials Science and Engineering Laboratory

A227, Bldg. 224, MS 8542

Phone: 301-975-6847; FAX: 301-975-4924

Email: yu-hsin.lee@nist.gov

Not member of sigma Xi

Poster category: Materials