Influence of composition and morphology on rheological properties of polyethylene/polyamide blends

The effects of composition and resulting morphology on rheology of blends of polyethylene and polyamide 12, two immiscible polymers having the same Newtonian viscosity but different elasticity, were studied in the whole range of volume fraction. The composition dependence of zero shear rate viscosity eta(0) and first normal stress difference N-1 show a positive deviation from the additivity law: eta(0) and N-1 increase gradually at low and moderate volume fraction of the dispersed phase, but remain almost constant in the phase inversion region. The variation of zero shear rate viscosity has been analysed, in relation to morphology observations, by an emulsion model as developed by Oldroyd in the case of droplet-type morphology and by a layer model which takes into account the simultaneous presence of droplets and fibres when the morphology is partially fibrillar. if the volume fraction of the dispersed phase is not too low, the first normal stress difference is proportional to shear rate, in agreement with the prediction of Doi-Ohta theory, as a result of morphology modifications during flow. The linear viscoelastic behaviour has been analysed using Palierne's model and the interfacial tension between the two polymers has been determined by fitting the dynamic moduli with this model. (C) 1998 Elsevier Science Ltd. All rights reserved.