Exercise Exfoliants

The disappearance of basal signals from a WAXD pattern is often considered a sign that exfoliation occurred. Considerable attention should be exercised in taking this condusion, though, because WAXD alone is not suffident to prove exfoliation [16,17,53,56-58]. Alternative explanations of the absence, or of the dramatic weakening, of a diffraction peak in composite materials could be poor dispersion quality, preferential orientation of the layers, or low clay content, rather than exfoliation. In order to correctly assess the degree of interaction between polymer and day, WAXD, SAXS, and TEM must be used complementarily. Extensive intercalation could separate day layers to a distance undetectable by WAXD but that can still be determined by SAXS [1,10,13,56,59-63]. Only the simultaneous disappearance of SAXS signals and TEM observations can confirm that exfoliation has occurred. 

Intercalation of the montmorillonite galleries with PP without full exfoliation was observed. Caution must be exercised when evaluating the tensile modulus results. The modulus of the polymer blends needs to be compared with and without montmorillonite present (as in the work above) to obtain a more valid comparison of the impact of the different montmorillonite composites on mechanical properties. PB 3200 would appear to be the best choice (as in the work above) for a PP-g-MA compatibilizer for the preparation of a PP-montmorillonite composite. The tensile modulus for a 5 wt.% organomontmorillite containing PP composite with 15 wt.% PB 3200 as a compatibilizer increased from 936 MPa with the hopper feed to 1037 MPa for the side-feeding protocol. The pure PP had a tensile modulus of 690 MPa. 

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