Preparation, characterization and properties of organoclay reinforced polyurethane nanocomposite coatings

A processing scheme is used to reinforce polyurethane coatings with an organoclay Cloisite 20A in three different weight percentages (1, 3 and 5 wt%). Transmission electron microscopy of Cloisite 20A-polymer dispersions shows exfoliation, intercalation and even agglomeration of clay layers. X-ray diffraction studies also indicate expansion in gallery spacing of organoclay layers in polyurethane coatings. Light scattering experiments shows the unimodal and bimodal particle size distributions for 3 and 5 wt% Cloisite 20A dispersions. Rheological behavior of these dispersions changes from quasi-Newtonian to strongly pseudo-plastic fluid. The power law index values decrease from 0.46 (0 wt%) to 0.29 (5 wt%) indicating increased shear thinning in coating formulation due to addition of Cloisite 20A. Although gloss reduces by 33%, maximum temperature of degradation improves by 27 °C in 5 wt% Cloisite 20A-PU coatings. A loading of 5 wt% Cloisite 20A enhances the mar resistance by 22%, while the char residue of polyurethane coatings increases by 6 times. Color changes ( CIEL* a* b*) in polyurethane nanocomposite coatings are insignificant below an addition of 5 wt% organoclay. Fourier transform infrared analysis shows that Cloisite 20A has good chemical compatibility with polyurethane and there is no change in basic urethane structure of the coatings.