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Clays and Clay Minerals; April 2004; v. 52; no. 2; p. 171-179; DOI: 10.1346/CCMN.2004.0520203
© 2004 Clay Minerals Society
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IMPROVED THERMAL STABILITY OF ORGANICALLY MODIFIED LAYERED SILICATES

Rick D. Davis1,*, Jeffrey W. Gilman1, Thomas E. Sutto2, John H. Callahan3, Paul C. Trulove4 and Hugh C. De Long4

1 National Institute of Standards and Technology, Building and Fire Research Laboratories, Gaithersburg, Maryland 20899-8665, USA
2 Naval Academy and Naval Research Laboratory, Code 6170, Washington, DC 20375, USA
3 FDA/CFSAN, HFS 717 Instrumentation and Biophysics Branch, 5100 Paint Branch Parkway, College Park, Maryland 20740, USA
4 Air Force Office of Scientific Research, 801 Randolph St. Room 732, Arlington, Virginia 22203-1977, USA

* E-mail address of corresponding author: rick.davis{at}nist.gov

Bromide-containing impurities were found to decrease the thermal stability of quaternary alkyl ammonium-modified layered silicates. Improved purification procedures completely removed bromide and led to a 20°C to >100°C increase in organic modified layered silicate thermal stability. Using mass spectrometry and thermal and electrochemical analysis, N,N-dimethyl-N,N-dioctadecyl quaternary ammonium-modified montmorillonite and fluorinated synthetic mica were found to degrade primarily through elimination and nucleophilic attack by these anions. The nature of residual bromides was identified and quantified, and the efficiency of removing these anions was found to be solvent dependent; sequential extraction, first ethanol then tetrahydrofuran, gave the best results. This exhaustive extraction method represents a viable alternative to the use of expensive, more thermally stable oniumion treatments for layered silicates.

Key Words: Alkyl Ammonium • Montmorillonite • Nanocomposites • Organic Modifier Degradation • Organoclay • Synthetic Mica






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