A mixture of seven immiscible "virgin" plastics, namely low and high density polyethylene (LDPE and HDPE), polypropylene (PP), polyvinyl chloride (PVC), crystal and high impact polystyrene (PS and HIPS), and polyethylene terephthalate (PET), in proportions representative of those currently found in post-consumer plastics containers, was compounded in a corotating twin-screw extruder. The mechanical properties of the blend were improved through the addition of relatively high concentrations of a dialkyl peroxide which was also found to drastically affect the blend morphology. The results are interpreted in terms of improved dispersive mixing favored by the similarity in the rheological behavior of the modified blend components, improved physical properties of certain blend components upon peroxide modification, and, possibly, enhanced interfacial adhesion.