Heterogeneous nucleation and self-nucleation of isotactic polypropylene with addition of nano-ZnO

Abstract

The influence of nano-zinc oxide (nano-ZnO) on the crystallization and melting behaviors of isotactic polypropylene (iPP) was investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and polarized optical microscopy (POM). The results indicated that nano-ZnO is an efficient β-nucleating agent for iPP. The relative content of β-crystal rises at first and then goes down with increasing nano-ZnO concentration and can reach 95.2% while incorporating 3% nano-ZnO during isothermal crystallization at 132 °C. The β-nucleating efficiency of nano-ZnO depends on its concentration and dispersibility in the iPP matrix. The lattice constants of nano-ZnO are a = b = 0.325 nm and c = 0.521 nm, and 0.325 nm is exactly half of the unit cell parameter in the c-direction of β-iPP. This lattice matching facilitates the formation of β-crystal. Moreover, the relationship between heterogeneous nucleation and self-nucleation of iPP with addition of nano-ZnO was also explored by adjusting the fusion temperature Tf. DSC measurements confirmed that the ordered structures of iPP inhibit β-crystallization induced by nano-ZnO. Meanwhile, the introduction of nano-ZnO also reduces the α-nucleating activity of the ordered structures. A possible interaction mechanism was proposed.