Poly(amic acid) (PAA)/organo clay nanocomposites and PAA/polyaniline-modified clay nanocomposite were prepared by in situ polymerization processes. The progress of condensation polymerization was followed by measuring the shear viscosity for both neat and filled PAA polymerizing solutions. The shear viscosity of the polymerizing solution increases quickly during the initial stage of polymerization followed by a slight increase all the stage of polymerization. The presence of clay expedites the initial stage of polymerization reaction as shown by a much higher shear viscosity for PAA/PANi clay polymerizing solution during the initial 30 mins of reaction, but results in a lower solution viscosity after a long polymerization time. The optical property for the poly(amic acid) solution with and without clay was studied by using UV/Vis spectrophotometry. Both PAA/organo clay and PAA/PANi clay solutions showed well resolved absorption in the visible region, between 500 and 600nm. There was no noticeable UV/Vis absorption peak in the visible region for samples prepared by ex situ method.
Polyimide (PI)/clay coatings were cast from the PAA/organo clay and PAA/PANi nanoclay composite solutions onto steel and Al substrates, followed by thermal treatments at varying temperatures. The degree of imidization (DOI) of neat and filled PI resin was studied as a function of the curing temperatures by using the attenuated total reflectance infrared spectroscopy (IR-ATR). Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were used to determine the morphology of PI/clay nanocomposites. SEM images show much larger clays for PI/organo clay nanocomposites than those for PI/PANi clay nanocoposites. TEM analysis shows that the clay platelets and tactoids are properly dispersed and oriented in the polyimide matrix. Wide-Angle X-ray Diffraction (WAXD) was utilized to analyze the structure of clays in the nanocomposites. The extent intercalation of clay improved with increasing imidization temperature and weight % of clay. The result suggests the existence of a hybrid clay structure in the nanocomposites cured at T≥150°C: unintercalated or marginally intercalated, and highly intercalated or exfoliated clay platelets.
Corrosion inhibition properties for neat PAA, PAA/organo clay, and PAA/PANi clay nanocomposite coatings were tested by using DC Polarization (DCP). PI/organo clay coatings show superior corrosion inhibition properties. The corrosion rate decreases drastically as curing temperature and clay concentration increases for PAA/organo clay nanocomposites.