Effect of the type of Montmorillonite on the Morphology and the rheological behaviour of Polypropylene Nanocomposite

C.O. ROHLMANN; M. D. FAILLA; L. M. QUINZANI

Rio de Janeiro, Brasil

Congreso; Fourth International Conference on Science and Technology of Composite Materials; 2007

Polymer/clay nanocomposites (PNC) are prepared by the intercalation and exfoliation of inorganic clay platelets in a polymeric matrix. Properties such as strength, gas permeability and thermal stability are found to be equivalent, and even superior, than in conventional microsized composites. In particular, PNC based in Montmorillonite (MMT) are among the most studied composites nowadays. This clay is constituted by ~1nm thick layers stacked in ~1mm average diameter particles. The use of MMT in PNCs requires an initial step of purification of the material followed by the interchange of the natural conterions by organophylic ones.  This step increases the interlayer spacing and improves the compatibilization with the polymer.  Furthermore, in the case of PNC based in polypropylene (PP), an anhydride grafted PP (PPg) is added to further improve the compatibilization. In the present work, blends of a PP (Petro­química Cuyo S.A.I.C.), a PPg (Uniroyal Chemical Co.) and different MMTs are analyzed.  The composites are prepared by melt mixing in a thermoplastic mixer.  The aim of the work is to perform a comparative study of the structural characteristics of the PNCs and their melt rheological properties as a function of the type of MMT and the organophylic surfactant used in the modification. All the blends considered have 5 wt% of MMT and 15 wt% of PPg. The  morphology of the clays and the PNCs is analyzed using scanning electron microscopy and x-ray diffraction, while the dynamic moduli of the materials were obtained in a rotational rheometer under different thermo-mechanical conditions. The results show that the degree of dispersion and exfoliation of the clay depend on the thermal stability of the clay, the degree of hydrophilicity of the surfactant, and on the thermo-mechanical history applied to the samples. The viscoelastic behavior of the PNCs show the same dependency.