Assessing an interaction between solid particles and a thermoplastic material in which the solid particles are dispersed includes combining a thermoplastic material with a multiplicity of solid particles to yield a heterogeneous mixture, processing the heterogeneous mixture to yield an unconditioned sample, conditioning the unconditioned sample to yield a conditioned sample, subjecting the conditioned sample to a ramping shear rate from an initial shear rate to a final shear rate, assessing a viscosity of the conditioned sample at a plurality of shear rates between the initial shear rate and the final shear rate, and assessing a value of a slope of a shear-thinning region for the unconditioned sample using a power-law equation.