Isothermal Crystallization Behaviors of Isotactic Polypropylene Nucleated with the Third Generation Sorbitol Derivative Nucleating Agents

Differential scanning calorimetry (DSC) was used to study the isothermal crystallization kinetics of isotactic polypropylene (iPP) nucleated with a third generation sorbitol derivative l,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS). The results show that the incorporation of DMDBS can greatly shorten crystallization half time (t1/2) and increase the crystallization rate of iPP. The Avrami exponents of both virgin iPP and iPP nucleated with DMDBS are close to 3, which indicates that the addition of the nucleating agent DMDBS doesn't change the crystallization growth patterns of iPP under isothermal conditions. The Hoffman theory is adopted to calculate the σe—interfacial free energy per unit area perpendicular to PP chains of virgin iPP and iPP nucleated with DMDBS. The result shows that the addition of DMDBS can decrease the σe value of iPP so that the nucleation rate of iPP is increased greatly.