A new composite SSEM_SF/FF computer model of solids conveying, melting and melt flow has been developed for starve fed/flood fed single screw extrusion using conventional and non-conventional screws, mixing and Maddock screws. 3D non-Newtonian FEM simulations using Ansys-Polyflow software have been performed for study of the polymer melt flow in these configurations to develop screw pumping characteristics which have been implemented into the composite model of the process. Starving and screw filling have been discussed and clarified via screw/die interactions. Experimental studies have been carried out for starve fed/flood fed extrusion of several polymers, incl. LDPE/PS polyblend. “Screw Pulling-out Technique” has been applied to investigate the material transport and melting in the machine. Pressure and temperature were measured, as well as power consumption was evaluated. CSM type of melting mechanism (contiguous solids melting) was observed for flood fed extrusion, but it was not observed for starve fed extrusion. A new melting mechanism for polyblend materials has been proposed, including conductive melting in the starve fed region, and dispersed melting in the fully filled region. A forward/backward scheme of calculation has been applied for composite modeling. Screw pumping characteristics based on 3D non-Newtonian simulations of the polymer melt flow in conventional and mixing configurations have been used to calculate pressure gradient back along the screw. A composite SSEM_SF/FF model has been applied for simulation of the experimental runs. The model predictions were consistent with experimental data. Keywords: Composite Modeling, Starve Fed/Flood Fed Extrusion, Polyblends, FEM Simulations. ACKNOWLEDGMENTS The authors would like to acknowledge support from National Science Center, Poland (DEC-2012/07/B/ST8/03327).