In the current study, an assessment of the melt-compoundingapproach upon the behavior of blast furnace slag (BFS) filledpolypropylene (PP) is reported. Two melt-compounding tech-nologies are compared in terms of thermodynamic considera-tions as well as final behavior of the produced compounds.For this comparison, three PP-BFS formulations are intro-duced, where non-treated BFS is melt-mixed with PP via (1)internal lab mixer (IM) and (2) co-rotating twin-screw com-pounder (TSC). PP-BFS compounds from both processes areformed into plates via compression molding, characterizedand tested for rheological, thermal and mechanical behavior.Processing parameters were evaluated for both processessuch as specific shear work, residence time and shear rates.In addition, the rheological, thermal and mechanical behaviorof comparable compounds are evaluated. The calculated spe-cific shear work values for IM and TSC are 0.15 and0.1 kW·h·kg–1. Calculated residence time for TSC is 55 s.Regarding the rheological behavior, it was found that meltmixing via both technologies did not show major differencesin complex viscosity or storage- and loss moduli values. DSCfindings show that crystallization and melting temperaturesof IM- and TSC formulations are comparable. Decreasedstrain values are noticed for TSC compounds, while tensilemodulus is found to be independent of process variation.