Nucleating agents/optical property

Nucleating Agents (optical property modifiers) Increasing crystallinity ... 

Polypropylene molecules repeatedly fold upon themselves to form lamellae, the sizes of which ate a function of the crystallisa tion conditions. Higher degrees of order are obtained upon formation of crystalline aggregates, or spheruHtes. The presence of a central crystallisation nucleus from which the lamellae radiate is clearly evident in these stmctures. Observations using cross-polarized light illustrates the characteristic Maltese cross model (Fig. 2b). The optical and mechanical properties ate a function of the size and number of spheruHtes and can be modified by nucleating agents. Crystallinity can also be inferred from thermal analysis (28) and density measurements (29). 

The incorporation of carbon nanotubes (CNT)s into polymer matrices has resulted in composites that exhibit increased thermal stability, modulus, strength, electrical and optical properties (33-35). Several investigations have concluded that carbon nanotubes can also act as a nucleating agents for polymer crystallization (36,37). 

Nucleating agents help to increase crystallinity in crystallisable polymer systems, and thus they also can be considered as optical property modifiers . 

Another side benefit that accompanies with the use of certain nucleants is improved clarity. Since clarity or transparency is evidently related to the crystalline structure of the polymer and the structure is determined by the conditions of crystallization, parameters characterizing crystallization must be also connected with the optical properties of a PP product. The peak temperature of crystallization (Tc) is one of the quantities often used for the characterization of the crystallization process and efficiency of nucleating agents. With increased crystallization temperature, the thickness of the lamellae increases well. Higher efficiency and concentration of nucleating agent lead to an increase of Tc (as determined by DSC) and decrease of the size of the spherulites. 

Polypropylene blown film which has excellent optical and mechanical properties was obtained using nucleating agents. The polypropylene composition contains a clarifier selected from the group of aromatic phosphoric acid ester metal salts and almniniitm-hydroxy-bis[2,2 -methylene-bis(4,6-di-t-butylphenyl)phosphate] in the qirantities from 0.01 to 5 wt%. ... 

Blown film is manufactured from metallocene-catalyzed polypropylene containing a-nucleating agent. The a-nucleating agent is a phosphate ester salt or a carboxylate salt added in quantity of 10 to 5000 ppm. The blown film has improved film forming properties and good optical and mechanical properties. ... 

All physical properties have influence on performance of nucleating agents but only the most relevant properties to their main contributions to the changes of the materials performance (crystallization, optical properties, and mechanical performance) are discussed below under separate headings. 

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