Improved Thermal Stability of Organically Modified Layered Silicates.
Improved Thermal Stability of Organically Modified
Davis, R. D.; Gilman, J. W.; Sutto, T. E.; Callahan, J.
H.; Trulove, P. C.; DeLong, H. C.
Clays and Clay Minerals, Vol. 52, No. 2, 171-179, 2004.
silicates; thermal stability; nanocomposites;
degradation; additives; x-ray diffraction; mass
spectroscopy; thermogravimetric analysis
Bromide containing impurities were found to decrease the
thermal stability of quaternary alkyl ammonium modified
layered silicates. Improved purification procedures
completely removed these bromide anions and led to a 20
DGC to > 100 DGC increase in organic modified layered
silicate thermal stability. Using mass spectroscopy,
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 quantified, and the
efficiency of removing these anions was determined 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.