Polyethylene applications have successfully demonstrated the use of calcium carbonate (CaCO3) for enhancement in properties such as productivity, impact resistance, and barrier performance. Because of high surface area and shape of the CaCO3 particles, it is challenging to disperse and stabilize high levels of CaCO3 within the polymer matrix. This issue was addressed by using a novel high speed quad screw extruder to examine the effect of screw speed (i.e., high shear rate) and screw design on resultant composites. Three different polyethylenes were compounded with 10, 40, and 70 %w micro CaCO3 at screw speeds of 1000, 1500, and 2000 rpm. The resultant composites were characterized for their rheological, dynamic mechanical, and morphological properties. The rheological behavior (frequency sweeps) were used to analyze the change in molecular weight, molecular weight distribution, and viscosity. In addition, the strain sweeps were used to characterize the linear viscoelastic region and the structure breakdown. Dynamic mechanical rheological testing was conducted to assess the elastic (storage) and viscous (loss) properties of these compounds. The morphology of composites (CaCO3 dispersion) was investigated using scanning and transmission electron microscopy.