INFLUENCE OF COMPOSITION AND MORPHOLOGY ON RHEOLOGICAL PROPERTIES OF POLYETHYLENE POLYAMIDE BLENDS/

The effects of composition and resulting morphology on rheology of ble nds of polyethylene and polyamide 12, two immiscible polymers having t he 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 sh ow a positive deviation from the additivity law: eta(0) and N-1 increa se gradually at low and moderate volume fraction of the dispersed phas e, but remain almost constant in the phase inversion region. The varia tion of zero shear rate viscosity has been analysed, in relation to mo rphology 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 disp ersed phase is not too low, the first normal stress difference is prop ortional to shear rate, in agreement with the prediction of Doi-Ohta t heory, as a result of morphology modifications during flow. The linear viscoelastic behaviour has been analysed using Palierne's model and t he 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.