Role of silane concentration on the structural characteristics and properties of epoxy-/silane-modified montmorillonite clay nanocomposites

Abstract

In the present work, sodium montmorillonite (MMT) was modified with varying concentrations of (3-amino propyl) triethoxy silane (APS) using water as the dispersing medium. Successful grafting of APS was corroborated using Fourier transform infrared spectroscopy (FT-IR). X-ray diffraction (XRD) studies of silane-modified clay revealed that the average d-spacing values increase at low silane concentration with the almost constant values at higher silane concentration. Total grafting yield of APS calculated using differential thermogravimetric results revealed that grafting yield decreases with increasing silane concentration. Epoxy-based MMT clay nanocomposites were prepared with different loading amounts of pristine (PM_0.0) and silylated clay (SM_4.4), and its influence on the mechanical, dynamic mechanical, and water uptake properties of the nanocomposites was investigated. The degree of intercalation of pristine or modified clay in the epoxy matrix estimated by XRD experiments exhibits a clear diffraction peak corresponding to the interlayer spacing d₀₀₁ of 14.8–28 Å. Characterizations of mechanical properties revealed that Young’s modulus and tensile strength increase with increasing concentration of the modified clay, while the fracture toughness shows a maximum at 6 wt% of clay. From the results of dynamic mechanical analysis, it was observed that the nanocomposites filled with silylated clay display higher storage modulus mainly at temperatures above the glass transition temperature. The equilibrium water uptake was reduced significantly on loading 6 wt% of pristine MMT, and this effect is more pronounced on loading silanized MMT in the nanocomposites when compared to the neat epoxy system.