Polyamidoamine as a clay modifier and curing agent in preparation of epoxy nanocomposites

Abstract

In the present study the commercial multifunctional fatty acid polyamidoamine (PAA) was for the first time simultaneously applied as a curing agent and clay modifier for epoxy/clay nanocomposites (NC) based on diglycidyl ether of bisphenol A. The montmorillonite (Cloisite (R) Na+) was modified with different quantities of partially and fully protonated polyamidoamine. The NCs with 0.5 wt% novel organoclay were prepared by solution intercalation method. The major aims of this paper are investigations of the effects of the composition of PAA modified clays on structure, mechanical, barrier properties and corrosion stability on steel substrates of NCs were studied. The thermogravimetric, flame photometry and X-ray diffraction analyses confirmed the efficient modification of clay surface with polyamidoamine, predominantly located within layers. The NCs exhibited an intercalated/exfoliated morphology and the presence of free amino groups and increased content of modifier facilitated dispersion of clay particles within the polymer matrix, as shown by electron microscopy techniques (SEM, TEM). Under an optimized loading of PAA (molar quantity of total amino groups per clay cation exchange capacity of 1.75), the layers in stacks were separated by 5.0 nm and high number of individual layers was present in NC. Clay modified by PAA with free amino groups showed increased storage modulus in the rubbery state, glass transition temperature of NCs, while dumping factor was decreased. The tensile test confirmed that introduction of flexible modifier on the epoxy/clay interface lead to increase in the ultimate tensile strenght and elongation at break by 31% and toughness up to 83%. The electrochemical impedance spectroscopy and permeability tests proved the pronounced barrier effect of clay particles against corrosive species and water vapor when high dispersion degree of clay in NC was achieved.