Abstract: The effect of three rare earth oxides, La₂O₃, Y₂O₃, and a mixture of rare earth oxides on the crystallization behavior of isotactic polypropylene (iPP) has been studied via differential scanning calorimetry (DSC). Avrami exponents n, the mechanism of nucleation, spherulite growth style and the crystal form of iPP have not been influenced badly by the rare earth oxides during the isothermal crystallization. However, a little of rare earth oxides will increase the crystallization rate and decrease the fold surface free energy, Oe, remarkable. This effect for Y₂O₃ most obvious and lowest for La₂O₃. The effect of the mixture of rare earth oxides is similar to the effect of Y₂O₃. By adding 1 wt% Y₂O₃ into iPP, the overall rate constant k in Avrami equation increases in one order.

Key words: polypropylene, rare earth oxide, isothermal crystallization kinetics, differential scanning calorimetry (DSC)