Nucleating agents are widely used to modify the properties of various polymers. The rate of crystallization and the size of the crystals have a strong impact on the mechanical and optical properties after conversion of the plastic, especially (but not exclusive) in polypropylene.
The addition of nucleating agents to the semi-crystalline polymers provides a surface on which the crystal growth can start. As a consequence, fast crystal formation will result in many small crystal domains. Cycle times in injection molding are reduced. Mechanical properties like flexural modulus, strength, heat distortion temperature and hardness will increase. The clarity and transmittance will improve.
Nucleating agents used for optimizing the optical properties are called clarifying agents.