Montmorillonite modification by cationic surfactants.

A.E. BIANCHI; M. FERNÁNDEZ; M. PANTANETTI; R. VIÑA; I. TORRIANI; R.M. TORRES SÁNCHEZ ; G. PUNTE

New Orleans

Congreso; ACA 2011 Annual Meeting; 2011

America Crystallographic Association

Montmorillonite modification by cationic surfactants. Enhancement of environmentally caring polymeric materials performance is a field of great activity and ecological interest. Polymers blended with natural minerals in the form of nanoparticles lead to composites with highly improved stiffness, thermal stability, decreased flammability and gas-barrier properties at low loading (< 5vol %). Natural clay minerals are a good choice to this end due to their availability, low cost and the possibility of changing their physicochemical properties by different methods. The first step in the development of nanocomposites polymer?silicate is the intercalation of cationic surfactants in the selected clay. In this work we present the synthesis process and physicochemical studies of organoclays obtained by intercalation of an Argentinean bentonite with hexadecyltrimethylammonium (HDTMA) and octadecyltrimethylammonium (ODTMA). The employed bentonite is predominately sodium montmorillonite (MMT), structural formula: [(Si3.89 Al0.11) (Al1.43 Fe0.26 Mg0.30)] M+0.41, cation exchange capacity (CEC): 174 meq/100g, isoelectric point (IEPpH): 2.7), external surface area 34.0 m2/g and total specific surface area 621 m2/g (Magnoli et al.). The organoclays (OMMTs) were produced by addition of 1 and 2 CEC of ODTMA and HDTMA to raw MMT diluted in deionized water. The successful development of new materials based on organically modified clays requires the knowledge of the surfactant intercalation and arrangement in the interlayer space of MMT and the factors that influence that array.  The four produced OMMTs were characterized by specific surface, SEM, SAXS, WAXS, apparent diameter of the particles (determined by DLS) and zeta potential. The entry of alkylammonium in the pillared galleries of the MMT modify the hydrophilic nature of MMT (OMMTs showed a drastic reduction in interlayer specific surface) and interlayer distance, d001=d, d: dMMT=1.25nm; dHDTMA1=2.09nm; dHDTMA2 =1.95nm; dODTMA1= 2.05nm y dODTMA2= 2.10nm. Observed OMMTs d001 values can be interpreted as mainly due to a paraffin-type monomolecular arrangement with different tilt values for both surfactants. SAXS profiles and SEM micrographs along with particles apparent diameter values indicated aggregates formation and several d values within each species. The reverse of the surface charge of MMT, evidenced by the positive zeta potential found in the OMMTs in all range of pH studied, induced by the adsorption of both alkylammonium on MMT, is discussed.   Magnoli. A. P. Et al. (2008) Appl. Clay Sci. 40, 63?71.