ABSTRACT
This chapter shows that flow is an integral part of any shaping operation, and, very frequently, it is useful to know quantities, such as the pressure drop needed to pump a polymeric fluid at a specified flow rate through a channel of a given geometry. It describes methods of measuring the stress response of polymeric fluids in well-characterized flow situations, presents the associated methods of data analysis, and provides the typical results. A reduction in entanglement density comes about in a sheared fluid because some polymer molecules, which would otherwise be entangled with the chain under consideration, pass through this sphere of influence with a residence time that is less than the fluid relaxation time. A specific form of the stress–relaxation modulus may be obtained by permitting the stress response in a polymer to be made up of an elastic contribution and a viscous contribution.
