A Study On Morphology, Structure And Rheological Behavior Of Polyethylene-Montmorillonite Nanocomposites Prepared By Melting Intercalation

The nanocomposites with exfoliated structure composed of low density polyethylene (LDPE), of organically modified montmorillonite and ethylene vinyl acetate copolymer (EVA) were prepared through two steps melt intercalating technique using a twin-screw extruder. The factors relevant to montmorillonite intercalation and exfoliation were analyzed through X-ray diffraction (XRD), thermogravimetry (TG), transmission electron microscope (TEM), scanning electron microscope (SEM) and Fourier transform infraredspectroscopy (FT-IR). The morphology, structure and properties for the composites were discussed. And the linear viscoelastic behavior, steady rheological behavior and the formation/evolvement of particles net structure for molten nanocomposites were studied using an advanced rheometric expansion system (ARES) and capillary rheometry.It is believed that the melt intercalation is a more efficient processing for formation of nanophase in polymer-layered silicates hybrids. LDPE intercalated into the space between the layers of organically modified montmorillonite (org-MMT), especially in the presence of compatibilizer EVA. The unstable stacking of layers of org-MMT was easily damaged under force and heat. Hence, it is very important to decide the process temperature for preparing the composites, and it was found that 200 ℃ was a upper limitation of temperature. On the other hand, the proportion of LDPE/EVA and adding of EVA were very important factors for composites preparing. The results shown that the nanocomposites with exfoliated structure could be prepared in the case of LDPE/EVA=77/20, EVA/org-MMT melted firstly and then extruded with LDPE using a twin-screw extruder.The layers of montmorillonite could disperse into polymer matrix uniformly rather than individually. Based on TEM images and FT-IR characteristics, it is found that most of layers formed as "pseudoparticles", which connected due to very stronginteraction. As a result, the tensile modulus of the composites were more tower than the corresponding values calculated by using Halpin-Tsai continuous equation, but higher than those of polymer matrix. While the steam barrier of films prepared by casting from the composites were enhanced as compared with that of the matrix film.The linear viscoelastic behavior of melts for nanocomposites with different content of montmorillonite modified by cetyltrimethylammonium bromide and octadecyltrimethylammonium bromide was studied. The results obtained through examining the dynamic storage module G', dynamic loss module G" and stress relaxtion module G(t) of the composites revealed that the linear viscoelastic properties of composites strongly depended on the loadings of montmorillonite exfoliated into the composites. With the increasing of montmorillonite content ,thecomposites showed a trend of pseudo-solidlike at lower frequencies, The montmorillonite layers could align along the stress direction, and as a result, the dependence of dynamic modules on the frequency was quite different before and after suffering from large amplitude oscillatory shear.The results obtained through examining loss tangent tan at deferent temperature and G' dependence on frequency ω of the composites revealed that the secondaryrelaxation asd G' of samples depended on the loadings of montmorillonite exfoliated into the composites. With the increasing of montmorillonite loading, the peak position corresponding to secondary relaxation for composites moved to higher and the peak values appeard higher, too. Time-temperature superposition principle could bee applied to G' dependence on CD, and the dependence of shifted factor aT on temperature demonstrated a linear relationship by a plot of In aT vs. T-1.The steady rheological measurements for nanocomposites melts were conducted.The results revealed that the melts of exfoliated nanocomposites with lower loading oforg-MMT exhibited shear-thinning even at lower shear rate as compared with polymers filled with common particles, while the melts flow depended weakl...