Nucleating agents efficiency

The main factors determining the efficiency of sodium salts of organic acids as nucleating agents for PET are alkalinity, solubility and thermal stability. These are widely varying for different families of products and a compromise has to be made between these properties. The more soluble and the more stable, then the... 

Figure 14.14 Sodium stearate is an efficient nucleating agent for PET since it scissions an ester bond and creates an ionic chain end which acts as the primary nucleation site. The disadvantage of this form of nucleation is that it leads to a reduction in the molecular weight of the polymer...

For evaluating the efficiency of the nanostructured interface for cell nucleation, the particle density of PPE, as a measure for the number of nucleating sites available for nucleation, is plotted versus the nucleation density observed for the foam (Fig. 21). For comparison, the previously found values of the uncompatibilized PPE/SAN blend are added. For PPE/SAN, even the relatively high number of PPE particles of around 5 x 10ncm-3 only leads to nucleation of approximately 2.5 x 1010 cells cm-3, i.e., only 1/20 of the potentially available PPE particles act as cell nucleating agents. Via compatibilization, however, not only the particle density of PPE and the nucleation density can be increased, but also the efficiency is strongly enhanced. While the number of cells directly scales with particle density, more than two foam cells are nucleated by one PPE particle. 

The effectiveness/efficiency of nucleation with (n-s) polymer-CD-ICs was observed to be at least comparable or superior to that produced by more traditional nucleation agents, such as talc, and for that matter pure CDs. The alteration of crystalline morphology achievable by using n-s polymer-CD-ICs as nucleants in melt-crystallization is demonstrated in Fig. 19. It is very clear that the morphology of PCL melt-crystallized in the presence of a small amount of (n-s) a-PCL-C-IC is very distinct from the pure melt-crystallized PCL. Crystal sizes are drastically reduced and more homogeneously distributed for the nucleated PCL. 

In this section we have demonstrated that certain nucleating agents based on substituted 1,3,5-benzene trisamides and bisamides are efficient additives to improve... 

Recycled material acts as a nucleation agent in polypropylene but is much less efficient than titanium dioxide pigment in this capacity unless higher generation regrind is utilized. 

Phthalocynine is known as efficient nucleating agent of the a form of polypropylene. The high crystalline structure of the fibres results from its high nudeation ability. Appearance of the small number of P crystals is surprising. 

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. 

Also, Amash and Zugenmaier [38] observed an increase in the crystallization temperature of polymeric matrix with the addition of cellulose fibers and MAPP, used as a compatibilizing agent. The DSC results clearly show that the addition of small amounts of cellulose fibers to PP increases the crystallization temperature of the polymer matrix. The effects observed can be explained by the assumption that the cellulose fibers act as efficient nucleating agents for the crystallization of PP. 

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