**8.2 Nucleating agents**

Nucleating agents are generally used to enhance the formation of nuclei for the growth of crystal in the polymer melt. A higher degree of crystallinity and a more uniform crystalline structure in the hard phase can be obtained by adding a nucleating agent in the polymer. Nucleating agents can be classified as inorganic additives (talc, silica), organic compounds (salts of mono- or polycarboxylic acids) and polymer. Nucleating agents may be used to enhance crystallinity of a hard phase segment.

#### **8.3 Colorants**

Colorants are often referred to as dyes and pigments. Generally, dyes are soluble in water while pigments are not. The colours from dyes are produced from the light absorption and they are transparent. Pigments produce colours from the dispersion of fine particles throughout the resin. Inorganic pigments are thermally stable than organic pigments. They are less transparent and resistant to migration, chemicals and fading. Some examples of inorganic pigments are oxides, sulfides, hydroxides, and other complexes based on metal.

#### **8.4 Flame retardants**

Most thermoplastics are flammable, burning easily when heated to high temperature. Flame retardants are added to polymer to delay the ignition and burning of polymer. Char-formers form a foamy porous protective barrier on the polymeric material to shield it for further combustion. Flame retardants acting in the condensed phase deposit a layer on the surface of polymer to prevent it from the heat source while flame retardants acting in gas phase interrupt the combustion chemistry of the fire.
