Assessing the nanoscale structure of clay epoxy nanocomposites by tuning the physicochemical and processing conditions

Abstract Organoclay/polymer nanocomposites are known to present improved mechanical properties, mainly when the organoclay is well dispersed or completely exfoliated in the polymer matrix. The objective of this work was to systematically evaluate the effect of different parameters, such as premixing procedure, role of the intercalating agent as well as the influence of the curing agent on the dispersion and intercalation/exfoliation state of organoclay in epoxy nanocomposites and how the extent of the dispersion affects the mechanical properties. For this purpose, two commercial organically modified montmorillonite (Cloisite 20A and Cloisite 30B) were dispersed within diglycidyl ether of bisphenol A (DGEBA) using different mixing approaches, namely conventional mechanical stirring followed by high-speed homogenization and/or ultrasonication. The dispersion state was evaluated before curing by means of X-ray diffraction (XRD), small-angle X-ray scattering (SAXS) and rheological measurements and after curing by SAXS, transmission electron microscopy (TEM), dynamic mechanical analysis (DMA) and mechanical properties. High-speed mixing combined with ultra-sonication resulted in better dynamic mechanical properties. The DGEBA/Cloisite 30B system cured with 4-methyl-tetrahydro-phthalic anhydride presented a better clay mineral dispersion in comparison with triethylene-tetramine (TETA)-cured systems. When the clay mineral was previously dispersed in acetone and submitted to high-speed mixing and sonication the dispersion of the clay mineral was even better. Epoxy networks containing Cloisite 30B and cured with anhydride presented both elongation at break and modulus significantly higher than those got with the other systems, including neat epoxy network. The previous treatment of clay mineral with solvent resulted in a marginal increase in tensile strength of the epoxy network and a decrease in modulus.