How do PP Nucleating Agents work?
A "Nucleator" is typically characterized as an insoluble particulate that increases the rate of crystallization.
When semi-crystalline polymers crystallize from the melt (typically during the cooling phase of a process), the lamellae organize from a primary nucleus to form complex macro-structures called spherulites. These spherulites continue to grow until they impinge on an adjacent spherulite at which point the growth ceases.
Properties of the polymers, including optical and physical characteristics depend on the end size of the spherulite structures and the crystalline orientation in the matrix.
In nucleated polypropylene, crystallization occurs earlier in the cooling process and happens at a faster rate. This allows decreased cooling time of the polymer. Also, nucleation density is much higher and crystal spherulite size is much smaller.
Figure 1 shows an illustration of the heterogeneous nucleation process versus a non-nucleated resin for comparison:
Figure 1: Illustration of the crystallization process in non-nucleated or nucleated matrix
Polypropylene is recognized as a relatively easy material to nucleate. This is because the rate of crystallization is low enough to allow the nucleating agent to have a direct impact on the nucleation density.