The dynamic crystallization and melting behavior of isotactic polypropylene-tungsten disulfide (iPP/IF-WS2) composites incorporating incorporating a beta-nucleating agent is investigated by X-ray diffraction and differential scanning calorimetry. A conventional melt-processing strategy is employed to generate new materials that exhibit variable alpha and beta polymorphism under the appropriate kinetic conditions. The results show that when the dual additive system is employed the nucleation ability on isotactic polypropylene not only depends on the nucleation efficiency (NE) and relative content of the individual alpha and beta-nucleating agents, but also on the cooling rates employed. The nucleating behavior of the additives is explained by competitive nucleation, and the correlation between crystallization and melting temperatures and relative content of alpha and beta-crystals of iPP in the nanocomposites is discussed.