Observation of stable flow - sharkskin

This section analyses the appearance of the extrudate under regimes corresponding to the stable branch of the flow curves [8, 22], i.e., before the first slope discontinuity and, in certain cases, before the jump in flow rate value. 

In conclusion, it seems that by using appropriate pol3uners and techniques, it can be demonstrated that sharkskin  

Lastly, it must be underlined that it is possible to significantly delay or eliminate the appearance of sharkskin, by considering the polymer flow through fluorinated dies [33, 39, chapter III.4. of this book]. Characterized by their particularly low surface energy, these type of dies cause the polymer shpping at the wall even in small flow regimes. Thus, the fluid could be extruded under low stresses and it doesn t crack. 

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