Thermal degradation chemistry of alkyl quaternary ammonium montmorillonite

The thermal stability of organically modified layered silicate (OLS) plays a key role in the synthesis and processing of polymer-layered silicate (PLS ) nanocomposites. The nonoxidative thermal degradation of montmorillonite a nd alkyl quaternary ammonium-modified montmorillonite were examined using c onventional and high-resolution TGA combined with Fourier transform infrare d spectroscopy and mass spectrometry (TG-FTIR-MS) and pyrolysis/GC-MS. The onset temperature of decomposition of these OLSs was approximately 155 degr eesC via TGA and 180 degreesC via TGA-MS, where TGA-MS enables the differen tiation of water desorbtion from true organic decomposition. Analysis of pr oducts (GC-MS) indicates that the initial degradation of the surfactant in the OLS follows a Hoffmann elimination reaction and that the architecture ( trimethyl or dimethyl), chain length, surfactant mixture, exchanged ratio, or preconditioning (washing) does not alter the initial onset temperatures. Catalytic sites on the aluminosilicate layer reduce thermal stability of a fraction of the surfactants by an average of 15-25 degreesC relative to th e parent alkyl quaternary ammonium salt. Finally, the release of organic co mpounds from the OLS is staged and is associated with retardation of produc t transfer arising from the morphology of the OLS. These observations have implications to understanding the factors impacting the interfacial strengt h between polymer and silicate and the subsequent impact on mechanical prop erties as well as clarifying the role (advantageous or detrimental) of the decomposition products in the fundamental thermodynamic and kinetic aspects of polymer melt intercalation.