Evaluation of the role of an ionic liquid as organophilization agent into montmorillonite for NBR rubber nanocomposite production

In this work we have shown the preparation of montmorillonite (Na + Mt) co-intercalated with a quaternary ammonium salt (hexadecyltrimethylammonium — HDTMA) and an ionic liquid (IL) (1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)imide — OMImTf2N) using a mechanochemical process. Changes in the structure of the organophilized montmorillonite were characterized using X-ray diffraction (XRD), thermal gravimetry (TG), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The presence of both cations (HDTMA and OMIm) into the clay mineral layers was confirmed by FTIR. XRD studies support that the co-intercalation process of the IL cation is more easily established in phases in which the interlayer space is not totally packed with HDTMA and an additional order in ionic liquid phase was observed when the IL amount exceeds 15 mass%. The addition of IL induced a thermal stability gain of 90 °C in comparison with the ammonium treated montmorillonite. The incorporation of IL in the ammonium based organoclays also displayed their better compatibility with the elastomeric matrix (NBR). Morphology studies by SEM of cryofractured surfaces evidence an improved interface interaction between the clay mineral and elastomer, indicating that ionic liquid has a direct and pronounced effect on the final clay polymer nanocomposites. This result can be assigned to the covered clay mineral particles mainly for higher IL content.