Modification of clays with ionic liquids for polymer nanocomponents

In attempts to prepare nanofillers with enhanced compatibility with a polymer matrix, cationic and anionic clays susceptible to exchange of their interlamellar ions with a variety of other cations or anions, were selected. In order to treat cationic clay, montmorillonite, which contains sodium ions as interlayer ions, reagents having cations differing in size and structure included three ionic liquids ([EMIM]+ [Br]-, [HXMIM]+ [Cl]-, and [Epty]+ [BF4]-). Results indicated that cationic exchange did occur from aqueous solution as confirmed by FTIR, EDX, WAXS, TGA, and elemental analysis. WAXS indicated a significant increase of interlamellar spacing as a result of intercalation, depending on the cation size. In addition, TGA demonstrated that thermal decomposition of the modified montmorillonites was dependent on the thermal stability of the ionic liquids intercalated. In anionic exchange with layered double hydroxide clays, a synthetic hydrotalcite susceptible to exchange of its interlamellar carbonate ions with a variety of other anions, was selected. Reagents having anions differing in size and structure included two colorless ionic liquids ([Epty]+[BF4]- and [Epty]-[CF3COO]-+ ) and a pH color indicator, bromothymol blue. Results indicated no exchange with the ionic liquids from aqueous solution as confirmed by FTIR, EDX, WAXS, elemental analysis and TGA. However, anion exchange did occur with calcined hydrotalcite (after removal of carbonate ions and water), which was reconstituted in the presence of aqueous solutions of the same ionic liquids. Ion exchange also took place with the much larger anion of bromothymol blue resulting in a colored clay. WAXS indicated a significant increase of interlamellar spacing as a result of intercalation, depending on the anion size. All montmorillonites modified with ILs, which were tested in the preparation of polypropylene nanocomposites, showed very small intercalation of polymer chains as confirmed by WXRD, although much higher in all cases than the pristine mineral. They also showed limited dispersion in the polymer matrix by comparison with commercial organoclays. Future work with different ionic liquids and/or polymer matrices of different polarity is recommended for improved intercalation and dispersion