Nucleating agents and clarifiers

Transparency of PP products can be efficiently improved both with traditional nucleating agents and clarifiers, which are various sorbitol derivatives. The improvement in the optical properties depends on the efficiency in destroying the spherulitic structure of PP or at least decreasing the size of the spherulites below a critical value. Strong nucleation... 

The results presented above and Figure 1 indicate that transparency is closely related to the crystallization and the crystalline structure of the polymer. Any effect which influences these factors will change transparency as well. Several publications indicate that the introduction of heterogeneous nucleating agents or clarifiers into PP homo- and copolymers considerably improves the transparency of the product. 

The first three materials listed in Table 11.6 are amorphous thermoplastics. CR-39 is a cross-linked, amorphous network (see Section 17.2). Most highly crystalline polymers are hazy because the crystals and the amorphous phases do not have the same index of refraction and light is scattered at the interfaces. Poly(4-methyl-l-pentene) is unusual in that the two phases have nearly the same index of refraction. The haze in crystalline polymers can be reduced if the crystallite size is very small. A sorbitol-based clarifier for polypropylene is bis(3,4-dimethyldibenzylidene) [25]. It acts as a nucleating agent and makes it possible to produce a water bottle with PET-like clarity. 

There appears to be no physical (e.g., crystal habit or morphology) or chemical (e.g., surface groups) correlation to identify which nucleating agent works best with which polymer matrix. However, it is known that dibenzylidene sorbitol works best with PP (it is sometimes called a clarifier because it enhances transparency), and inorganic benzoate salts are successful with PET. 

Polypropylene can have its clarity and transparency improved by orientation, or by use of clarifying/nucleating agents. 

Nucleation and clarity 10 High crystallization and processing rates, high haze in cloudy PE and PP Nucleating agents for higher properties, clarifying nucleators for clearer PP containers... 

Table 10.1 Summary of Nucleating and Clarifying Agents Discussed in this chapter...

Strength and modulus Fundamental tests for strength and stiffness, along with HOT testing, reveal to what extent a clarifier also serves as a useful nucleating agent. 

Early clarifying and nucleating agents sometimes resulted in difficult ejection from the mould, or gave rise to organoleptic problems. The suppliers have addressed these issues in recent years. 

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%. ... 

Polypropylene nonwovens or yams are produced by extruding a mixture of polypropylene and P-nucleating agent or certain clarifiers to form the improved polypropylene filaments." The P-nucleating agent comprises at least one of N, N -dicyclohexy 1-2,6 naphthalene dicarboxamide and NJ-Star NU-lOO from Rika."... 

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