A study of polymer/clay nanocomposite formation by melt-intercalation process

A comprehensive study was performed to determine the mechanisms of intercalation of polymers into montmorillonite clays and the formation of polymer/clay nanocomposites in the melt compounding process. Polymer nanocomposites are considered formed from montmorillonite clay fragments when such clay fragments have dimensions in one direction of order 10--100 A or 1 to 10 nm. Various polymers including polyolefins, polybutadiene, halogenated polymers and acrylonitrile copolymers were melt-compounded with natural and organic modified montmorillonite clays. A total of 19 polymers and 6 clays were studied. X-ray diffraction (WAXS) and transmission electron microscopy (TEM) characterizations showed the separation of montmorillonite layers and the formation of polymer nanocomposites.; All chlorinated polymers, vinylidene fluoride containing fluorinated copolymers, and acrylonitrile copolymers formed polymer/clay nanocomposites with organoclays. Systems consisting of non-polar polyolefins and polybutadiene or natural montmorillonite clay could not make polymer nanocomposites.; It was concluded that the polarity of the polar polymers and organophilicity of the organoclays lead to the formation of polymer nanocomposites. The dielectric constant i.e. dipole moment of polymers could be used to predict the formation of polymer nanocomposites. Polar polymers with high dielectric constants generally form polymer nanocomposites with commercially available organoclays. However, the degree of organophilicity of organoclays also affects the formation of nanocomposites.; Various organic modified montmorillonite clays were investigated including commercial organoclays containing the quaternary alkyl ammonium compounds. Generally the latter showed excellent compatibility with polar polymers. Polystyrene creates nanocomposite with Cloisite(TM) 20A, but not with Cloisite(TM) 30B. The primary (12ALA), secondary (DOA), and tertiary (TOA) organoclays showed poor compatibility with polymers compared to the quaternary organoclays.; Thermodynamic equilibrium in the formation of polymer/clay nanocomposite in melt compounding processes was interpreted by modeling heat and entropy of mixing for the free energy of formation. Exothermic interaction between polar polymers and quaternary amine organic groups seems to be essential to the nanocomposite formation.