Rheology of metallocene polyethylene-based nanocomposites: Influence of graft modification

Several compounds were prepared by melt compounding a metallocene linear low density polyethylene with a graft-modified polyethylene and an organically modified clay in different proportions in a twin screw extruder. X-ray diffraction, transmission electron microscopy, and rheology were used to characterize the extent of intercalation of the silicate galleries. Incorporation of minimum weight fraction of 2% clay and 50% maleated polyethylene was found to introduce radical changes in the rheological behavior of the nanocomposites. Broadening peaks in x-ray diffraction indicated increasing dispersion of silicate galleries into polymer as a function of graft modification. With higher incorporation of maleated polyethylene, possible networking was seen with solidlike response beginning to appear at low frequencies. Flow activation energy was found to decrease with incorporation of clay. Relaxation spectra determined using a parsimonious model were found to extend to higher relaxation time scales with exfoliation. Finally, the Cox-Merz rule was found to fail over the whole range of shear rates for exfoliated compounds, indicating increased interactions in the matrix resulting in highly anisotropic distribution of individual silicate layers. (c) 2006 The Society of Rheology.