A filled polymer melt as a new thixotropic model system and insights on efficacy of two thixotropic models

TEVP (thixotropic elasto viscoplastic) fluids exhibit phenomenon such as shear thinning, yield stress, viscoelasticity and thixotropy. A filled polymer melt system consisting of LDPE (low density polyethylene) filled with fumed silica is presented here as a material system that exhibits the different features expected from a general TEVP fluid. It is evaluated through different rheological protocols such as steady shear, step shear, start up shear and flow reversal. Further it is compared against the experimental data corresponding to the standard TEVP material system, namely the fumed silica suspension from literature to understand the influence of dispersing medium on the breakdown and rebuilding time scales of the microstructure. It is observed that the proposed formulation which is simpler (consisting of only two constituents), with hardly any solvent evaporation, chemical aging and yields better viscoelastic transients compared to fumed silica suspension. In the proposed formulation, structural breakdown occurs on longer time scales. The rheological data of the proposed filled melt system is then compared to predictions from two different mathematical models. The comparison yields insights into the efficacy of the two models, providing some guidelines for improvement.