Abstract
Viscosity is the property most used with molten plastics. It relates the shear stress to the shear rate in steady simple shear flow, which is the deformation generated between two parallel plates, one of which undergoes linear displacement. For viscoelastic fluids, two other quantities are needed for a complete description of the stress field, and these are the first and second normal stress differences. The viscosity and the two normal stress differences are functions of shear rate that are called the viscometric functions, and flows governed by these are called viscometric flow s. In addition to simple shear, other viscometric flows include flow in straight channels and rotational flows between concentric cylinders, between a cone and plate and between two disks. Flow in an extruder is dominated by the viscometric functions, mainly the viscosity. This chapter describes the dependence of viscosity on shear rate, temperature, molecular weight and its distribution, tacticity, comonomer content, and long-chain branching.
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Dealy, J.M., Wang, J. (2013). Viscosity and Normal Stress Differences . In: Melt Rheology and its Applications in the Plastics Industry. Engineering Materials and Processes. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-6395-1_2
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DOI: https://doi.org/10.1007/978-94-007-6395-1_2
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