Extrudate swell in some dilute elastic solutions

An experimental programme has been carried out to obtain data for the isothermal swelling of dilute viscoelastic fluids based on the polyisobutylene-polybutene system. The fluid was thus a constant viscosity one and so the observed swell was predominantly due to elastic effects alone. To establish the experimental rig and procedure, preliminary results for the creeping flow of a Newtonian fluid, based on a polybutene, were acquired. The Newtonian results, showing a creeping flow swell of 13.8%, demonstrated that the rig and procedure were satisfactory for the formation of free, isothermal jets. The viscoelastic results were quite unexpected, showing that dilute elastic solutions can exhibit significant swelling despite the fact that the recoverable shear is small (S _R < 0.1). These results qualitatively confirm a recent numerical study 1].