Effect of reaction temperature on grafting of γ-aminopropyl triethoxysilane (APTES) onto kaolinite

The effect of the temperature (175, 185, 195 and 220 °C) on the grafting of γ-aminopropyl triethoxysilane (APTES) on the interlayer hydroxyl groups of kaolinite pre-intercalated with DMSO were investigated using Fourier transform infrared spectroscopy, X-ray diffraction, thermal analysis and elemental analysis. The APTES-modified kaolinite prepared at 220 °C showed a structure with high content of APTES and high thermal stability, in which the APTES molecules were grafted on to the inner-surface hydroxyl groups of kaolinite and arranged in the form of cross-linked monolayers. The APTES-modified kaolinites prepared at 175, 185 and 195 °C exhibited inhomogeneous interlayer structure with pseudo-bilayer arrangements composed of grafted APTES molecules and hydrogen-bound DMSO or APTES molecules coexisting with monolayer arrangements. The monolayer arrangement of APTES corresponded to the basal spacing of about 1.00 nm and the pseudo-bilayer arrangement 1.73–1.89 nm. High reaction temperature was advantageous to the formation of the monolayer arrangement by promoting the exchange of the DMSO molecules by APTES molecules in the interlayer space of kaolinite, as well as the transformation of hydrogen-bound APTES molecules into grafted molecules.