The Effect of Spray‐Freeze Drying of Montmorillonite on the Morphology, Dispersion, and Crystallization in Polypropylene Nanocomposites

The spray‐freeze drying (SFD) technique was applied to sonicated aqueous suspensions of spray‐dried montmorillonite clay (MMT) to produce highly porous agglomerates (SFD‐MMT). Both MMT (used as a reference) and SFD‐MMT were subsequently incorporated in polypropylene (PP) via melt compounding to produce 2 wt % nanocomposites with and without maleic anhydride grafted polypropylene (PP‐ g ‐MA). Polypropylene nanocomposites containing SFD‐MMT exhibited thinner silicate flake layers compared to large agglomerates in PP/MMT nanocomposites. SFD‐MMT particles became even more finer in the presence of PP‐ g ‐MA (i.e., in PP/PP‐g‐MA /SFD‐MMT) where it hindered PP crystallization instead of serving as nucleation sites for the PP crystallization during rapid cooling. SFD‐MMT improved the thermal stability of PP/PP‐ g ‐MA by 30°C compared to only 5–8°C for MMT/nanocomposites. MMT acts as a heterogeneous nucleating agent in the nucleation‐controlled PP nanocomposites, but the hindrance effect was observed for the PP/PP‐ g ‐MA with SFD‐MMT. PP/PP‐ g ‐MA/SFD‐MMT exhibited twice the edge surface energy as compared to PP/PP‐ g ‐MA/MMT. The incorporation of both types of MMT raised the tensile moduli of PP and PP/PP‐ g ‐MA, with no improvement in their tensile strength and a decrease in the elongation at break. The PP/PP‐ g ‐MA/SFD‐MMT showed brittle failure. POLYM. ENG. SCI., 60:168–179, 2020. © 2019 Society of Plastics Engineers