Dispersion efficiency of montmorillonites in epoxy nanocomposites using solution intercalation and direct mixing methods

Abstract

The major aims of this paper are the investigation of the effects of the mixing procedure and the montmorillonite (Mt) surface modification on the structure (optical microscopy, XRD, TEM, SEM), rheological, mechanical properties (DMA, tensile test) and corrosion stability (electrochemical impedance spectroscopy) of clay mineral/epoxy nanocomposite (CPN). Two series of CPN samples were prepared based on diglycidyl ether of bisphenol A (DGEBA) and polyamidoamine curing agent with three organophilic Mt and sodium-montmorillonite (1 wt%). Mt were mixed with DGEBA solution in the powder (direct mixing) and in the form of dispersions, preswollen in a commercial coating thinner (solution intercalation). The commercial Mt (Cloisite 30B) modified by quaternary alkylammonium ions bearing hydroxyl groups and especially Mt functionalized by primary (HDA(+)-Mt) alkylammonium ions, at loadings close to cation exchange capacity (CRC), were significantly swollen by thinner and further uniformly dispersed into CPN. Meanwhile, low gel volumes in thinner were found for more hydrophobic Mt (Cloisite 15A). The compatibility of Mt with solvents was well described by solubility and Flory-Huggins interaction parameters. In contrast to the direct incorporation of Mt powders in CPN, swelling enhanced intercalation of epoxy matrix into Mt, and for HDA(+)-Mt based CPN interlayer spacing reached 4.4 nm. The usage of HDA(+)-Mt organoclay and solution intercalation procedure provided the highest enhancement in rheological parameters (G', G", of Mt/epoxy dispersions and glassy storage modulus, Young's modulus and barrier properties of cured CPN.