流变讲义.pptVIP

* * * * * * * * * Measurements at low shear rates provided information as to the bubble characteristics of the film blowing resin. The resin with good bubble stability and consistent gauge uniformity had a higher viscosity (at low rates) than the poor resin. Measurements at high shear rates provided information as to how the PE extruded, because extrusion is a high shear rate process. The material that extruded well had a lower viscosity than the one that extruded poorly. The better film blowing resin was the one with higher viscosity at low rates, and lower viscosity at high rates, as shown in Figure * * * * * * * * * * * * * * * * * * Have a viscosity profile, on the log scale one cannot achieve a zero shear rate, so it is extrapolated from very low shear rates In polymers, the zero shear region is proportional to the molecular weight Cox merz basically transforms oscillatory frequency information information into shear rate information * * * * * * * * * * * * * * * Roll the silicone “putty” into a long flexible cylinder. You can grab the silicone “snake” on both ends and slowly move your hands apart = the silicone will flow and deform mostly homogeneously. If you move your hands apart fast, the materials will instantaneously break. Conclusion A material deforms macroscopically, when internally the material’s structure has the time to reorganize itself (by diffusion of the the polymer chains). If the external applied deformation is too fast for these internal reorganization to take place, the material breaks. If the material has plenty of time for reorganization., a material behaves linear and the material properties are independent of the total deformation. If not enough time for the reorganization of its structure is availbale, the material starts to behave non-linear, the material rheological properties depend on the total applied deformation and eventually the material breaks * * * * * * * * * * * * * * * * * Medical and Industrial PSA PSA Performance window