Experimental evaluation of the pseudotime principle for nonisothermal polymer flows

We have applied a series of start-up of uniaxial extensions to very high strain followed by stress relaxation. A potential temperature change was applied during the stress relaxation. We used two thermorheological simple polymers; a linear polystyrene and a branched low density polyethylene. Experiments performed with temperature changes during the stress relaxation were shown to be identical with isothermal ones in the “pseudotime”, within the accuracy of the experiments. This verifies that the pseudotime approach seems to be the general basis for nonisothermal microstructural modeling for flow of polymers. The pseudotime is given as ξ(t) = ∫to 1/aT(T(t1))dT1, where aT are the well established time-temperature superposition shift factors, calculated from the past temperatures (at time t0) in a particle path

Elongational Viscosity of Monodisperse and Bidisperse Polystyrene Melts

Submitted to J. Rheol.The startup and steady uniaxial elongational viscosity have been measured for two monodisperse polystyrene melts with molecular weights of 52 kg/mole and 103 kg/mole, and for three bidisperse polystyrene melts. The monodisperse melts show a maximum in the steady elongational viscosity vs. the elongational rate, ε, of about two times 3η_0 whereas the bidisperse melts have a maximum of up to a factor of seven times the Trouton limit of 3η_0. The Wiest model which incorporates anisotropic drag and finite extensibility may be used to interpret the results in molecular terms.Class of 1960 Fellowship Fund

Catastrophic failure of polymer melts during extension

Numerical flow modeling has been applied to study the break of monodisperse polymer melts during extension. These continuum mechanical based computations are within the ideas of the microstructural ’interchain pressure’ theory. Calculated breaks, a result of small initial sample imperfections, agree with experimental observations