Studies on wall-slip in entangled polymeric liquids

Commercial plastic extrusion processes are severely limited by the occurrence of instabilities above a critical production rate. There are different types of instabilities observed in an extrusion process. In this work, we are primarily concerned with the stick-slip instability, which occurs above a critical wall shear stress during extrusion and is characterized by fluctuations in flow rate and pressure drop as well as the bamboo-like distorted extrudate surface. The stick-slip instability is believed to occur because of a sudden slip of the polymer chains at the die wall either due to disentanglement or debonding mechanism. In this work we attempt to theoretically understand this phenomenon through empirical and molecular models. Initially, we use the framework a transient network theory, which is suitable for describing dynamics of entangled liquids to model the slip phenomenon. We consider the case of polymers flowing over a high adhesive energy surface. More Info

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