A composite model has been developed to simulate a starve fed single screw extrusion of thermoplastics. The model is based on combining melt conveying models with new melting models. Illustrative computations are made for low-density polyethylene and polypropylene at various operating conditions. Simulations are made for axial fill factor, pressure, temperature, and melting profiles. The results are validated experimentally. (C) 2013 Society of Plastics Engineers