Investigations On Wall Slip And Crystallization Behaviors Of POE/PS Blends

In this thesis, the wall slips of polyolefin elastomer (POE) and polystyrene (PS) atdifferent temperatures under dynamic shear conditions were investigated. Thedetermination of wall slip length, b and its dependence on temperature and thecharacter of materials were discussed. Then the crystallization behaviors of POE andPOE/PS blends were investigated by dynamic rheology. And the influences of thedispersed PS in the POE/PS blends on their crystallization behaviors were studied.Similar to the well-known “Time-Temperature Superposition”(tTs), a “Time-GapSuperposition”(tGs) method was established and applied to the obtained angularfrequency sweep data at selected different gaps at certain temperatures, and thesuperposition validity of the data was proved by Maxwell model theoretically. Theshift factors of different curves of storage modulus dependent on angular frequency ofPOE or PS at different selected gaps were obtained by shifting to correspondingmaster curves. On the basis of the relations between the zero shear viscosity and theshift factors, the shift factor was found to be a function of the wall slip length and thegap between the parallel plates. Thus, the wall slip length and the actual experimentalcurves under dynamic shear conditions can be obtained. The results showed that thewall slip showed significant dependence on material character and temperature.Generally, wall slip occurs more heavily at low temperatures while more weakly athigh temperatures, and the tGs was not valid below a certain temperature. The wallslip behaviors of POE is quite different from those of PS and the wall slip of POE ismore heavily dependent on the decreasing temperature while the wall slip of PSchanges a little with the decreasing temperature.The non-isothermal crystallization behaviors of POE and POE/PS under dynamicshear conditions within the linear viscoelastic regions showed that the applied angularfrequency and the dynamic shear stress had no observable influences on thecrystallization behaviors of POE and POE/PS blends. Because the wall slip increasedwith decreasing temperature, the experimental errors of low temperature part of thenon-isothermal crystallization curves were much larger than those of high temperaturepart. Though the errors at low temperatures may be relatively large, from thedifferences between the vGP diagrams of POE and POE/PS blends, the errorsoriginated from wall slip can be ignored and the influences of dispersed PS in POE/PScan be observed easily. It revealed that the dispersed PS shows a different influence on the crystallization behaviors of POE revealed by rheological parameters, such asstorage modulus, complex viscosity and so on, when compared with the formedcrystal structure of POE during crystallization progress. This indicated that the crystalstructure of the crystallization progress cannot be simply handled as hard spheres inrheological characterization of the crystallization progress as in some suspensiontheoretical theories.