A new slit-radial die capable of simultaneously obtaining steady state shear viscosity η _ γ ð Þ and the average first normal stress difference coefficient ⟨Ψ 1 _ γ ð Þ⟩
T/2 processes in the material and on the correlation with the decrease in static sealing force. To begin with, however, theoretical model concepts will be discussed relating to thermodynamic and kinetic processes during cooling of a polymer melt, i.e. the process of freezing in molecular mobility and volume shrinkage.
Flow instabilities cause various problems in extrusion blow-or flat film processes. Especially shark skin is affected by molecular structure. This phenomenon is analyzed in various scientific works using apparatus that are complex or difficult in operation. A new set-up, now available is being presented as an option for new and existing capillary rheometers or lab extruders, consisting of a special designed die, a fast responsive transducers system and evaluation software. The software allows the evaluation of diverse pressure frequency regimes causing flow instabilities and generate statistics. Measurement examples are given for different shear rates and polymers. The shark skin effect can be detected even before it is visible on the extrudate. The measured frequency regimes are related to molecular parameters
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