additives | Clarifiers and nucleators
low-cost product from China coming onto the market following the expiry of at least one important patent for DMDBS (Millad 3988). This caused some western suppliers to adjust their prices – as well as emphasise the quality of their own products. More recently, supply of Chinese product has become restricted following Chinese government crack-downs on pollution. These have resulted in several hundred production plants producing various materials to be shut down. Conse- quently, price fighting seems to have abated. Emerald points out that sodium benzoate can be used
Graph showing the effect of nucleation on ozygen gas barrier and water vapour transmission rate for and 0.96 density 0.95 MFI HDPE film without nucleator (in grey) and with nucleator (orange) Source: Milliken Chemical
has been used for many years as a nucleating agent for polypropylene, enabling injection moulded parts to be removed from the mould at temperatures that are 15-20°C higher than would otherwise be the case. The use of a nucleating agent for polypropylene is
especially critical, says additive supplier Emerald Kalama Chemical, as PP normally has a relatively low rate of crystallisation. “Sodium benzoate’s balance of efficiency and economy makes it a reliable choice for this application. Emerald is the world’s largest producer of benzoic acid and a leader in sodium benzoate. Emerald has been working on the development of optimised sodium benzoate forms in recent years. For example, it now produces a dense form that grinds or micronises well without the handling issues associated with powder. “The result is that it takes less energy to micronise than other particle forms of sodium benzo- ate,” the company says. “Micronisation aids in dispersibility, which is
Figure 1: An unoriented PE spherulite. Amorphous tie chains (in
yellow) between lamellae provide an easy path for gas permeation through the matrix
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important when a pre-blend is used for incorporation. Many nucleating agents struggle with dispersibility since they are not soluble in the resin. Sorbitol-based clarifiers are another solution that can help, but at much higher cost and use levels relative to inorganics. By refining our dense grade, we preserve the economy of our customers’ operations while allowing for greater dispersibility.” In terms of economics, Compounding World under- stands that prices of sorbitol clarifiers had fallen as a result of
N COMPOUNDING WORLD | May 2017 C
www.compoundingworld.com
in polypropylene products for food contact, helping PP to be used as a replacement for PET. It recently completed a $40m expansion to double benzoic acid expansion at its Rotterdam, Netherlands, operation. This expansion significantly supports increased capabilities for sodium benzoate production. A further expansion to increase sodium benzoate capacity by another 30,000 tonnes/yr is currently in the planning stage. Milliken says its Hyperform HPN “third generation”
nucleators provide an excellent balance of physical properties. They are also said to override the nucleating effect of pigments, meaning that high part quality is possible regardless of the colour used. Hyperform HPN achieves an improvement in
stiffness of around 10%, when compared to PP nucleated by other means, while still retaining the same impact behaviour as a non-nucleated resin. The claimed improvement in stiffness over non-nucleated PP is 25-30%. “The unique isotropic shrinkage behav- iour of each Hyperform HPN nucleator allows dimen- sionally stable, non-warping tailor-made PP solutions to be developed for use even in demanding injection moulding applications like caps and closures, and in the elevated temperature environments like in some automotive and appliances applications,” Milliken says. Dimensional stability is maintained at temperatures
up to 25°C higher than when used with a non-nucleated resin and up to 10°C higher than a conventional nucleated resin, the company claims. It also claims advantages in cycle time reductions.
Better barrier
Darin Dotson, Senior Scientist in Milliken & Company’s Chemical Division, explains that nucleat- ing agents also have the ability to improve the barrier proper- ties of polyethylene film.
Passive barrier ingredients such as talc or calcium carbonate or montmorillonite nanoclay are proven in their ability to enhance
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