The Dispersion Of Montmorillonite In Alkane Solvents And Characterization Of The Organophilic Montmorillonites Formed In Situ

Organophilic montmorillonites (OMMTs), usually with surface modified by quaternary ammonium surfactants (QASs), are widely used as rheology control agents, as fillers to prepare nanocomposites and as adsorbents of organic pollutants. Moreover, dispersion of OMMTs in the organic medium is an important step for preparing clay-based composites and for rheology controlling of nonaqueous suspensions. For example, when used as fillers, high dispersibility of the OMMT particles in the polymer matrixes is beneficial for the improvement of the materials’ properties.It is supposed that the original purpose of surface-modification for montmorillonites (MMTs) is to improve their compatibility with the organic medium, and then it will be easy to improve their dispersibility in the organic dispersion medium. Thus, if the surfaces of MMTs can be modified in the final dispersion medium (e.g. alkane solvents, polymer matrixes, etc.), then the series steps of fabricating OMMTs could be eliminated. And more importantly, it will be energy-efficient and more beneficial for commercial applications. Therefore, in order to understand the mechanism for natural MMT dispersion in nonpolar dispersion medium, the dispersion processes of Na-MMT in alkane solvents was studied here. The research results will be useful for selecting compatibilizers and optimizing processing conditions for preparing clay-polymer composites from pristine clay. Also it will be helpful to provide a new method to control the rheological behavior of dispersions in alkane solvents.The main contents of the thesis are as follows:1. The dispersion of Na-montmorillonite particles in alkane solventsSome QASs can dramatically improve the dispersibility of Na-MMT in alkane solvents at high temperature (in a dissolved state for the QASs) according to our previous observation. Thus, the dissolution behavior of some QASs in GTL and octane was observed firstly in the experiments with the aim to determine the reaction temperature for the dispersion experiments. The effect of dioctadecyldimethylammonium chloride (DODMAC) on the dispersibility of Na-MMT in GTL was primarily observed by optical microscope. And the rheological behavior of MMT suspensions obtained by in situ organo-modification method (ISOM) was studied and compared with OMMT suspension with the aim to explore the feasibility of using the ISOM instead of using OMMTs in practical applications. The viscosity curves of the MMT suspensions formed by ISOM suggest that this method could be used to control the rheological behavior of dispersions in alkane solvents. And it is shown that the QASs were adsorbed on the surfaces of MMT in alkane solvents through an ion exchange reaction according to the characterization results of the OMMTs synthesized in octane. More importantly, the mechanism for natural MMT particles dispersion in alkane solvents was also proposed based on the former experiment results.2. Synthesis of organophilic montmorillonites in octane and their characterizationSeries of OMMTs were synthesized in octane using Na-MMT and DODMAC, and they were characterized by X-ray powder diffraction (XRD), thermogravimetric analysis (TGA, and differential thermogravimetric analysis-DTG), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) to further demonstrate surface modification of natural MMT in alkane solvents and explore the feasibility of preparing OMMTs in alkane solvents. Furthermore, the OMMT synthesized in octane was also expected to be used as a novel material in the application fields of traditional OMMTs.