Reinforcement of elastomeric polypropylene by nanoclay fillers

Polypropylene (PP) was prepared by metallocene catalysts so as to have a stereoblock structure, with isotactic sequences long enough to give crystallites functioning as crosslinks, but small enough in number to have the atactic chains predominate in a surrounding elastomeric matrix. The resulting thermoplastic elastomer was then blended with organically modified clays to document the conditions required to exfoliate the clay layers in a way to maximize the chances for good reinforcement. Some experiments included the use of modified PP as a compatibilizing agent or a commercial silica, for reference purposes. The clays were clearly superior to the silica, which was found to be ineffective for reinforcing this elastomer. The nanoclay fillers did provide improvements in modulus but not toughness, because of corresponding decreases in extensibility. Resistance to creep also remained a problem, presumably due to the clay layers interfering with the growth of the crystallites needed to form a robust network structure.