Rheology and flow behavior of suspensions of nanosized plate‐like particles in polyester resins at the startup of shear flows; Experimental and modeling

Abstract Applications of organoclays to polymer resins are potentially of great technical interest. This research targets preparation and characterization of nanocomposites of organoclays in an unsaturated polyester resin (UP). The nanocomposites with two distinct dispersion levels were compounded in a complex multisteps mixing process at three concentrations and subsequently their microstructures were characterized by XRD. The solution‐state rheological properties of layered silicate/UP were measured in the start‐up of steady state in the simple shear mode and analyzed based on our observations of internal structure of nanoparticles dispersion. Strong shear thinning behavior caused by increasing particle alignment induced by the shear field was observed for the suspensions. Effects of nanoparticles loadings and shearing on transient viscosity of the UP resin were examined. The experimental results show that increasing shear time in nanosuspension preparation steps and hence improvements of nanoplate dispersion in the polyester resin give rise to viscosity of the suspensions. A theoretical analysis of the motion of rigid ellipsoidal particles in a Newtonian fluid based on the thermodynamic approach and Jeffery's analysis of the motion of ellipsoid particles with an interaction term was developed to determine the orientation state of disc‐shape layers and then, the expression for the extra stress tensor was calculated to predict transient viscosity and normal stress differences. It is found that the thin oblate particles have significant orientation preference in the shearing direction. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers