Thermal and anticorrosive properties of polyurethane/clay nanocomposites

Abstract

A montmorillonite clay has been modified with two different quaternary ammonium salts, dilauryldimethylammonium bromide (LD) and 4,4′-diaminodiphenylmethane (AP), to form the corresponding organophilic clays, LDM and APM. Two series of PU/clay nanocomposite materials, PU/LDM and PU/APM, were then prepared by the reaction of appropriate amounts of PPG, TDI and 1,4 butandiol, followed by addition of the various amounts of LDM or APM. The X-ray diffraction patterns and transmission electron micrographs of the nanocomposites revealed that the modified clay galleries were exfoliated or intercalated in the polyurethane matrix. In comparison with the corresponding pure PU, the results of the TGA and LOI measurements showed that the thermal stability and the flame retardancy of the PU/clay nanocomposites were significantly enhanced due to the presence of the dispersed nanolayers of the organophilic clay in the PU matrix. Using the Tafel method, the results of the electrochemical measurements, which included the corrosion potential, polarization resistance and corrosion current, showed that all the PU/clay nanocomposites, even with low clay loading, in the form of coating on stainless steel disk (SSD) exhibited better corrosion protection over the pure PU. The SSD coated with the composite containing 2 wt% of APM showed the lowest corrosion rate, which was one order lower than that of the SSD coated with the pure PU.