Epoxy composites based on amino-silylated MMT: the role of interfaces and clay morphology

Epoxy-based composites containing sodium montmorillonite (MMT) modified by silylation reaction with 3-aminopropyltriethoxysilane (A1100) and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (A1120) were prepared. The effect of MMT chemical functionalization, as well as inorganic content and dispersion method (i.e. sonication or combination of sonication and ball-milling) on the morphology and mechanical and thermal properties of composites was thoroughly investigated by X-ray diffraction analysis, dynamic mechanical and tensile static analysis, nanoindentation measurements and cone calorimeter tests. Morphological characterization showed that the MMT particles are only slightly intercalated by epoxy molecules. Tensile stress, elongation at failure and toughness of the epoxy composites based on silylated MMT were found to be improved. The presence of 1 and 3% wt/wt of A1100 and A1120 silylated MMT clays allowed the tensile elastic modulus to increase respectively of about 10 and 15% with respect to the pristine epoxy matrix. The overall results showed that 1) the silylation of MMT clays is a valuable method to improve the interfacial interaction between filler and epoxy matrix and 2) the interfacial interaction plays a role more significant than the clay morphology (i.e. the extent of clay intercalation/exfoliation) over the composite properties.