A collaborative investigation into the rheology of some polystyrene and polyethylene melts
This report is a compilation of the work carried out by different laboratories participating in the IUPAC Working Party on 'The Relationship of Performance Characteristics to Basic Parameters of Polymers'. The object was to study the relationship between processing and fundamental molecular structure. As a step in this direction participating laboratories have made various rheological measurements on six molten polymers: two polystyrenes, two low density polyethylenes and two high density polyethylenes. Each pair consisted of one material with a narrow molecular weight distribution and one with a broader molecular weight distribution. Measurements of viscosity in steady flow, dynamic viscosity, flow birefringence and stress-relaxation have been carried out. The participants are in general agreement about the relative shapes of the flow curves for steady shear flow and their temperature dependency although full agreement about the absolute values of the viscosities has not been obtained at all shear rates. A definite correspondence between the dynamic viscosity | η*(ω) | and the steady flow viscosity η(q) is found. Good agreement is found between spectra of relaxation times calculated from G'(ω), G"(ω) and from stress-relaxation after steady shear flow. Flow birefringence measurements demonstrated that increasing polydispersity implies increasing elasticity.