Modification of montmorillonites with thermally stable phosphonium cations and comparison with alkylammonium montmorillonites

Alkylammonium montmorillonites have onset temperature of degradation in the same temperature range used for compounding of thermoplastics, thus, requiring more thermally stable organic cations. In the current study, phosphonium, imidazolium and pyridinium ions differing in their chemical architecture (length of alkyl chains, number of phenyl groups etc.) were exchanged on the surface of montmorillonites. The montmorillonites with two different cation exchange capacities (CECs) were used. The thermal behavior of the modified montmorillonites was analyzed by thermogravimetric analysis. To achieve quantitative insights into the onset of degradation, temperatures to reach 5% and 10% mass loss and peak degradation temperatures were compared. Time to reach 1% mass loss was also calculated in the dynamic TGA. The surfactants used in the study were more thermally stable than the conventional alkylammonium cations due to their delayed onset as well as peak degradation temperatures. The time required to attain certain extent of degradation was also much higher in the case of phosphonium montmorillonites, thus, confirming their better thermal resistance. Though the degradation temperatures as well as profiles of the modified montmorillonites with different CECs were similar, the dynamic TGA revealed better thermal behavior of the higher CEC montmorillonite. The X-ray diffraction studies also concluded that optimal modification of the montmorillonite surface could be attained, thus, confirming the high potential of phosphonium montmorillonites for nanocomposites.

TGA thermograms of 2C18N●Mt880, 4C8P●Mt880 and 4PhP●Mt880 montmorillonites.Figure optionsDownload as PowerPoint slideHighlights
► Thermal comparison of phosphonium and alkylammonium montmorillonites.
► Dynamic TGA gained insight into thermal resistance of modified montmorillonites.
► Effect of chemical structure of organic cations and CEC on thermal behavior.