Advanced nucleating agents for polypropylene

The present short review aims to summarize advanced nucleating agents for polypropylene (PP). Reviewing the relevant literature, we focused on powerful nucleators that are capable of significantly increasing the crystallization temperature of the polymer at very low working concentrations and also serving as clarifying agents. The nucleation mechanism and efficiency of these compounds are discussed in detail. The nucleating agents were divided into groups according to their tendency to induce monoclinic (α), hexagonal (β), or orthorhombic: (γ) PP cell geometries. The major α-nucleators and clarifiers are sorbitol-based compounds that speed-up the polymer crystallization due to gelation phenomena and induction of epitaxial crystallization by the metal salts of substituted aromatic heterocyclic phosphate. Among β-nucleators, N,N'-dicyclohexyl-2,6-naphthalene dicarboxamide was found to be very efficient and its nucleation ability was highly concentration dependent. In addition, it was shown that nucleation efficiency of a nucleator can be significantly increased by a new dispersion method comprising its solubilization in a microemulsion. Moreover, the nucleator (HPN-68) increased the γ-modification present in the polymer.