Abstract: The effects of La₂O₃, Y₂O₃ and mixed rare earth oxides on the crystallization, melting behavior and the dynamic mechanical properties of isotactic polypropylene in its composites with oxides have been investigated by means of DSC and viscoelastometry. Y₂O₃ and the mixed rare earth oxides appeared to be an a and β-nucleator and La₂O₃ is an α-nucleator for iPP. The crystallinity degree increases in order of PP/Y₂O₃,PP/mixed rare earth oxides,PP/La₂O₃ and pure iPP. Tanδ values of the samples containning both α and β-phases are lower than that of the iPP and PP/La₂O₃ in the region near T_g relaxation. Dynamic storage modulus E in the PP/Y₂O₃ and PP/mixed rare earth oxides was higher than that of PP/La₂O₃ and iPP in the range of -50℃ to 50℃, but lower in 50℃ to 145℃.These results are attributable to the β-phase of polymer crystal in the samples.

Key words: differential scanning calorimetry, polypropylene, rare earth oxide, dynamic mechanical property, crystal phase