Polyproplene Nanocomposites Via Melt Intercalation:Formation,Exfoliation,Morphology And Property

Polymer melt intercalation is a more versatile approach to make polymer layered silicate nanocomposites, which has been most widely investigated in recent years. The thermodynamics and kinetics theories involved in polymer melt intercalation have also been intensively reported. However, most of the theoretic simulations are too ideal to describe the formation of polymer melt intercalation. The formation mechanism of polymer nanocomposites is the key to the development of nanocomposite. The final properties of the fabricated articles depend on mainly the exfoliation and dispersion of the platelets. In this work, Polypropylene (PP) /montmorillonite (MMT) nanocomposite made by melt intercalation was chosen to study the melt intercalation process, exfoliation mechanism, morphology and properties of polymer nanocomposites.First, The formation process and exfoliation mechanism were investigated by WAXD and SEM. Based on the results from melt compounding time, temperature, shear force, a model of nanocomposites formation and exfoliation was proposed. At the same time, influences factor in nanocomposite formation were also discussed. We found that the melt intercalation process has occured in one minute and MMT layers may aggregate as the increasing of the compounding time. The final structure of nanocomposites depends on the interaction between polymer and silicate, the contentof compatibilizer, shear force, compounding time, melt temperature and polymer melt viscosity.In order to improve the dispersion of MMT in PP matrix, the prepared PP/MMT nanocomposites via direct melt intercalation were further subject to oscillating stress achieved by dynamic packing injection molding. Shear induced morphological changes were investigated by WAXD, SEM and TEM, as well as Instron. The original nanocomposites possess a partly intercalated and partly exfoliated morphology. A transformation of intercalated structure into exfoliated structure was found after shearing, and more homogeneous dispersion of MMT in PP matrix was obtained. On the other hand, the orientation of PP chains in PP/MMT nanocomposites becomes very difficult under external shear force, which indicates that the molecular motion of PP chain intercalated between MMT layers is highly confined.Most of articles on polymer nanocomposites focus on the importance of the chemistry used to modify the surface of the clay, usually montmorillonite(MMT) and characterization of the nano-scale structure obtained. The role and importance of processing was also discussed recently. However, few papers concerning the correlation between morphology of MMT and mechanical properties were reported. In order to better understand the tensile behavior of PP/ Montmorillonite(MMT) nanocomposites, and further improve the reinforcement efficiency, we prepared the PP nanocomposites via direct melt intercalation using conventional twin-screw extrusion. The macroscopic and microscopic dispersion of MMT in PP matrix was verified by XRD and TEM, combined with SEM. While the tensile property was obtained by video-controlled tensile set-up, which gives true stress-strain curve. The orientation of silicates platelets and the degree of exfoliation are two key factors to determine the reinforcement efficiency. The other properties of nanocomposites are also discussed.The crystal morphologies were investigated by PLM, WAXD, and SAXS. It is found that exfoliation MMT layers can serve as the nucleating agent, which speed up the crystallization rate of the nanocomposites and also causes the decreasing of crystal size. The melting point and lamellar of PP nanocomposite were found decreased, compared with the pure PP, which is an indication of a strong interaction between PP and MMT. In this case, it can be considered that PP crystallizes in a confined space.