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Isothermal crystallization behavior of isotactic polypropylene (iPP) nucleated with three cyclic carboxylate nucleating agents, namely, sodium bicyclic[2,2,1] heptane dicarboxylate (HPN-68), sodium benzoate (Be-Na), and sodium salt of hexahydrophthalic acid (HHPA-Na), was investigated by using differential scanning calorimetry. The classical Avarmi method was used to evaluate the isothermal crystallization behavior of iPP. The nucleus density was obtained by the calculation model of Lamberti based on the Avrami method of crystallization kinetics from calorimetric crystallization curves recorded under isothermal conditions. This method was able to measure nucleus density and growth rate of nucleated iPP, for which the nucleation phenomenon was substantially heterogeneous. The addition of nucleating agents shortened the crystallization halftime (t1/2) and increased the crystallization rate of iPP under isothermal crystallization, eventually increasing the nucleus density of iPP nucleated with nucleating agents for finishing crystallization under higher crystallization temperature, which was larger than that of virgin iPP. The results of polarized optical microscopy also showed that the nucleus density and crystallization rate were greatly increased with addition of nucleating agents. In these three nucleating agents, HPN-68 had the best nucleation effect, and iPP nucleated with HPN-68 had shorter crystallization halftime and higher nucleus density than iPP nucleated with Be-Na and HHPA-Na. [ABSTRACT FROM AUTHOR]

The incorporation of a nucleating agent into isotactic polypropylene (iPP) is one of the most important and widely used methods to improve performance in the polypropylene industry. Aromatic heterocyclic phosphate salt is a kind of highly effective nucleating agent for iPP and one of the typical products is a compound nucleating agent based on 2, 2-methylene-bis (4, 6-di-tert-butylphenyl) phosphate hydroxyl aluminum (commercial product name: ADK NA-21). In this paper the isothermal crystallization kinetics of iPP nucleated with the α-nucleating agent NA-21, investigated using differential scanning calorimetry (DSC), is described with the crystallization data being analyzed by using the classic Avrami method. During isothermal crystallization the addition of nucleating agent NA-21 dramatically shortened the crystallization half time (t1/2) of iPP under the same conditions and the crystallization activation energy, ΔE, decreased from 422 kJ/mol for virgin iPP to 369 kJ/mol with the addition of NA-21. Thus, the addition of NA-21 significantly increased the crystallization rate of iPP. [ABSTRACT FROM AUTHOR]