The rate of the morphology development of immiscible polymer blends is closely related to the rates of melting of the polymer constituents. A two-zone model was developed to describe the rate of melting of the polymer pellets of mixtures of two semicrystalline polymers in an internal batch mixer. The mixing chamber was divided into two zones: high temperature and high shear zone, and low temperature and low shear zone. Melting was assumed to occur mainly in the first zone. Moreover, pellets were assumed to be spherical, and melting proceeded from the outer-surface to the core in a gradual manner. For a given pellet, the rate of melting depended, among other things, upon the number of passes through the high shear and high temperature zone and the time it experiences therein. The validity of the model was confirmed experimentally in terms of the number and weight fraction of solid pellets as a function of mixing time.