Flow Behavior of Polymers

Flow Behavior of Polymer Blends as Affected by Interchain Crosslinking... 

It is well known that LCB has a pronounced effect on the flow behavior of polymers under shear and extensional flow. Increasing LCB will increase elasticity and the shear rate sensitivity of the melt viscosity ( ). Environmental stress cracking and low-temperature brittleness can be strongly influenced by the LCB. Thus, the ability to measure long chain branching and its molecular weight distribution is critical in order to tailor product performance. 

The term pseudoplastic is somewhat outdated because there is nothing pseudo in the flow behavior of polymers. In this book we use the term shear thinning, which well describes the phenomenon. 

Even at a phenomenological level, the flow behavior of polymers differs significandy from that of low-viscous liquids such as water. The flow behavior of polymer melts is markedly dependent on the applied shear stress o, the shear rate y, and on time. Elastic effects and normal stresses also occur in practice, and their effects can either help or hinder the processes underway. 

Polymer chains anchored on solid surfaces play a key role on the flow behavior of polymer melts. An important practical example is that of constant speed extrusion processes where various flow instabilities (called sharkskin , periodic deformation or melt fracture) have been observed to develop above given shear stress thresholds. The origin of these anomalies has long remained poorly understood [123-138]. It is now well admitted that these anomalies are related to the appearance of flow with slip at the wall. It is reasonable to think that the onset of wall slip is related to the strength of the interactions between the solid surface and the melt, and thus should be sensitive to the presence of polymer chains attached to the surface. 

Takahashi H (1990) Flow behavior of polymer melts under extremely high shear rates and flow analysis of injection molding. J Rheol (Jpn) 18 172-9. 

In most cases the elastic response of filled polymers is severely reduced with respect to that of the polymer, though occasionally fillers may form an entangled structure with the melt exhibiting an anomalous elastic response. The study of the flow behavior of polymers filled with interacting particles presents serious complications. A major one is the agglomeration of... 

---