Relationship Among Rheology, Morphology, And Properties Of Pp/eva Blends Prepared Under Different Flow Fields

Polypropylene (PP) is widely used in automotive, household appliance, chemical and package industries. But the lack of toughness hinders the application of PP. Toughening modification of PP is the intention of this paper, and PP/EVA blends were prepared. In this study,70/30 PP/EVA blends were mixed through different flow fields (shear mixing field and chaotic mixing field) and through changing the screw speeds of single screw extruder. The samples were collected with sampling devices at four locations along the extrusion direction. And the samples collected along the extrusion direction were compared from rheology, phase morphology, and mechanical property. The mixing capabilities of three screw elements(conventional, chaos, and pin elements) used in this experiment in single extruder were simulated by finite element method. Through phase morphology, the relationship among flow field, rheology property, phase morphology, and mechanical properties was investigated.The result of rheological test and scanning electron microscopy (SEM) observation of blends indicated that chaotic mixing facilitated to form interpenetrating laminar, thinner laminar, co-continuous and fine droplets phase morphology. The dynamic complex viscosity and dynamic elastic modulus for the sample with droplets phase morphology were higher than sample with laminar and co-continuous phase morphology at lower frequencies, and the value became higher when diameters of droplets became smaller. The dynamic elastic modulus for the sample with co-continuous phase structure presented a solid-like response at lower frequencies. The Bousmina model was used to predict dynamic complex modulus of blends and the results were compared with experimental values. The result indicated that dynamic complex modulus could be predicted more more accurately by the Bousmina model for the sample with droplets phase morphology.Mechanical properties test showed that EVA increased the Izod impact strength but decreased the tensile strength of PP. The samples with co-continuous and interpenetrating laminar phase morphology had the highest Izod impact strengths. The Izod impact strengths of this two kind of samples were 12.2kJ/m2 and 9.7kJ/m2, which were 4.7 and 3.7 times of the Izod impact strength of pure PP respectively. The sample with droplets phase morphology had the highest tensile strength, and tensile strength increased when the diameters of droplets decreased. The result of simulation showed that the dispersive mixing, distributive mixing and chaotic mixing were the best for chaos screw element. The combination of simulated and experimental results indicated that chaotic mixing facilitated to form thinner laminar, co-continuous and fine droplets phase morphology. The dynamic complex viscosity and dynamic elastic modulus of blends increased when the dimension of dispersed phase decreased. For the blends with different phase morphology, this paper quantitatively developed the relationship of the mechanical properties and the continuity of dispersed phase for the first time, and the result showed that the Izod impact strength increased when the continuity of disperse phase increased. For the blends with droplets phase morphology, the Izod impact strength and tensile strength increased when matrix ligament thickness decreased.