Strategies for optimizing polypropylene-clay nanocomposite structure

The structure of nanocomposites produced by melt-mixing polypropylene and 5 wt % of organically modified layered silicates with varying amounts of different maleated polypropylene compatibilizer grades has been analyzed with X-ray diffraction, transmission electron microscopy (TEM), and melt rheology. The extent of delamination in different nanocomposites has been quantified from analysis of several TEM images for each specimen by a product of the single particle volume fraction and the intrinsic viscosity of such particles, This measure correlated directly with the low shear relative viscosity of the molten composites (relative to the silicate free mixture of polypropylene and compatibilizer). The results also indicate that the acid number alone is not a good predictor of compatibilizer effectiveness, i.e., the amount required for exfoliation. The molar ratio of functional groups to compatibilizer chains is found to be a better parameter for ranking compatibilizer effectiveness than the acid number, which is a weight ratio, With higher values of the molar ratio, lower concentrations of compatibilizer are required for significant exfoliation. With the highest molar ratio compatibilizer, an optimum compatibilizer concentration of about 10 wt % leads to a composite with the most exfoliated structure.