Effect of composition on crystallization behavior for polypropylene catalloys

Effect of composition on crystallization behavior for polypropylene catalloys ( PP-cats) was studied by using differential scanning calorimetry (DSC) and polarized optical microscopy (POM) The decrease of melting point for PP-cats indicates the existence of stronger interaction between the propylene homopolymer and the ethylene-propylene random copolymer (EPR) in PP-cats. The isothermal crystallization kinetics of PP-cats in the early stage could be described by the Avrami model, and a comparison with that of pure iPP was carried out. It is found that the crystallization of PP-cats proceeds with instantaneous nucleation and three-dimensional growth. The overall crystallization rate of PP-cats is higher than that of pure iPP and increases with the increase of the EPR content. However, the spherulite growth rate of PP-cats appears slower than that of pure i PP and decrease with the increase of the EPR content,which is ascribed to the difficulty in moving of propylene chains due to the higher viscosity of PP-cats melt. Furthermore, the results of morphology observation reveal that the nucleation density of PP-cats is rather higher than that of pure iPP. It is suggested that the higher overall crystallization rate of PP-cats is a result of the nucleation effect of the EP content.