The rheology of aramid platelet suspensions

Abstract

AbstractThe flow responses of aramid platelets (fibrids) suspended in a mixture of corn syrup and water at loadings of less than 1% were determined in steady shear, oscillatory shear, transient shear, and extensional flow. The effects of fibrid size, concentration, and suspending medium viscosity were examined. These suspensions exhibit a high zero‐shear viscosity, strong shear thinning with power law indices as low as 0.2, an infinite shear viscosity, and thixotropy. Steady shear viscosity data over six decades of shear rate were described very well by traditional models such as the Carreau or Cross equations. The platelets appear to form an interacting, flocculated network at rest that is the reason for the large relative viscosity. The largest platelets, however, appear to curl or fold and offer the least flow resistance during shear flow. The structure formed at rest is easily destroyed, and this is the reason for the observed shear thinning. In extensional flow, large Trouton ratios are observed even at very low fibrid concentrations, and these increase with the true aspect ratio, indicating that the fibrids are fully unfurled in the strongly orienting extensional flow. These rheological properties make fibrid suspensions good candidates for thickeners in sealant, caulk, and adhesive applications. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers