Fabrication of partially exfoliated and disordered intercalated cloisite epoxy nanocomposites via in situ polymerization: Mechanical, dynamic mechanical, thermal and barrier properties

Abstract

Clay minerals, especially montmorillonite (Mt), have emerged as a subject of enormous scientific interest due to their unique atomic structure, high cation exchange capacity, high aspect ratio and large surface area. Clay polymer nanocomposites have established a unique position among technologically important materials because of their extensive and potential applications. Herein we have fabricated cloisite epoxy nanocomposites (CPNs) from diglycidyl ether of bisphenol A (DGEBA) epoxy and modified nanoclay, cloisite 93A using triethylenetetramine (TETA) as a curing agent. The major objective was to examine the static and dynamic mechanical properties and the performance of these CPNs for barrier resistance and thermal stability. Determination of cross link density (CLD) of CPNs by Flory–Rehner equation and activation energy by Coats–Redfern procedure were also a focus of the present study. The cloisite layer exfoliation in CPNs was monitored by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and further corroborated using transmission electron microscopy (TEM). Static mechanical properties of CPN were characterized in terms of tensile and flexural properties. Moreover, dynamic mechanical and thermal properties were evaluated by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) respectively. XRD and TEM revealed that the cloisite distribution in the epoxy matrix is of the partially exfoliated kind at lower level loadings and intercalated at higher loadings. The enhancement of mechanical properties of CPNs was to the level of 15% increase in tensile strength and 23% in flexural strength at very low cloisite loadings. The interfacial interactions brought about by cloisite 93A also benefited the thermomechanical properties to a large extent in the form of improved glass transition temperature and an impressive enhancement in storage modulus. Results based on equilibrium swelling experiments revealed that a maximum of 61% increase in barrier performance was achieved by the addition of 5 phr (per hundred gram of resin) cloisite. CLD measurements demonstrated an 11% increase in CLD at 1 phr cloisite loading. TGA results revealed that cloisite can impart greater thermal stability to pure epoxy. All the properties were correlated with the dispersion state of the cloisite in the epoxy resin matrix.