Study on morphology change and viscoelasticity of PP/PE blend under shear flow

The morphology change and viscoelastic behavior of polypropylene/polyethylene blend systems under shear flow was investigated. Polypropylene homo-polymer (PP-A), polypropylene block-copolymer including ethylene-propylene copolymer part (PP-B) and linear low density polyethylene (PE) were used for this study. The steady and dynamic viscoelasticities under shear flow were measured. Mix rule was not adapted for the rheological properties at long times. The relaxation modulus of PP-A and PP-B decreased as a function of the time, but that of both PP/PE blends showed 2-step relaxation mode. The swelling ratio of PP-A and PP-B increased according to the increase of shear rate. Oil the other hand, shear rate dependence of the swelling ratio of PP became small by addition of PE. The morphology of capillary strands after shear flow was observed by TEM. As a result, the morphology change of PP-B was small for wide ran-e of shear rate. The droplets size was large and it strongly orientated to flow direction at low shear rate region for both PP/PE blends. Then, the size and orientation of droplets were reduced due to the increase of the shear rate. It was concluded that the swelling behavior of both PP/PE blends was affected by morphology change according to the shear rate.