Study on morphology evolution, orientational behavior, and anisotropic phase formation of highly filled polymer-layered silicate nanocomposites

Morphology evolution, anisotropic phase behavior, and orientational behaviors of the highly filled polymer-organically modified layered silicate nanocomposites are investigated by using synchrotron small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and polarized light microscopy (PLM). Two kinds of polymers, maleated polypropylene and maleated polyethylene were used as a matrix polymer. The final morphology of both polymer-organically modified layered silicate nanocomposites evolves via four stages; intercalation, dual states of intercalation and exfoliation, ordered exfoliation, and disordered exfoliation in sequence as the concentration of silicate decreases in the nanocomposites. The morphology evolution of nanocomposites is determined by balancing an interaction between polymer and silicate against interactions between silicate platelets such as a steric interaction and an attractive interaction, which depends on the concentration of silicates. Both the nanocomposites show the optical anisotropy above 12 vol % clay originating from the ordering of silicate layers. The layered silicates subjected to shear flow show the orientation behavior that the silicate platelet's normals are perpendicular to the flow direction. Degree of orientational order changes with the concentration as well as shear rate in a complex manner. Up to an intermediate concentration, the extent of order is enhanced with the clay concentration. In contrast, at high concentrations, the extent of order decreases or increases according to the type of nanocomposite. The differences are discussed through the consideration of the morphology, the particle-particle interaction, and the rheological property of the nanocomposites.