Nucleating and clarifying agents for polyolefins

Abstract

Nucleating agents are used in semi-crystalline polymer systems (mainly polyolefins) to increase the rate of crystallization. These agents increase degree of crystallinity and lamellae thickness and, hence, improve stiffness and strength. In addition to altered mechanical characteristics, clarifying agents do also improve optical properties. This paper provides a brief overview on nucleating / clarifying agents. The efficiency of such products (e.g. Na-benzoate, sorbitol acetals) for polypropylene (PP homopolymer, PP copolymer) is evaluated. The clarifiers Irgaclear D ((1,3:2,4)-dibenzylidene sorbitol) and Irgaclear DM (1,3:2,4-Bis-(p-methylbenzylidene) sorbitol) provide a 3-dimensional fibrillar structure upon cooling from the polymer melt. This magnified nucleation density yields spherulites with reduced size (< lmicron) - in comparison to non-nucleated products. Addition of Irgaclear to polypropylene leads to increased clarity, reduced haze and enhanced stiffness of molded parts. Higher recrystallization temperatures results in shorter cycle times and increased throughput during the molding process.