ADDITIVES | CLARIFIERS AND NUCLEATORS
Right: Beta nucleation technology is used to make micro-porous films for Li-Ion battery separator films
Relative advantage Jacoby points out, however, that new products must offer some advantage relative to existing products and that is usually measured in terms of higher performance and/or lower cost. At present, most commercially available nucleants and clarifiers increase stiffness but not impact strength, while beta nucleating agents increase impact strength but can result in lower stiffness. He says that, in terms of future development, nucleating agents that simultaneously improve stiffness and impact strength would be highly desirable. As well as improved stiffness and strength, other important factors include clarity, faster cycle rates, lighter weight parts and lower cost. Jacoby has worked extensively on development and commercialisation of beta nucleating agents for PP. While working for Amoco he developed and patented a product and process using beta nucleated PP to produce breathable polypropylene films for protective clothing and roofing mem- branes. Today, such technology is used in battery separators in lithium ion batteries. He also patented
a process using beta nucleation to reduce the weight and cost of thermo- formed PP food packaging. While working with Mayzo, he developed beta nucleant masterbatches for use in
markets including thermoforming, breathable films, geotextiles and injection moulded products. His research has found beta nuclea-
tion particularly useful for improving the properties of PP in moulded applications
that require high impact strength without a significant sacrifice of stiffness. “Beta nucleation also dramatically broadens the processing window for producing thermoformed containers and improves material distribution, leading to higher rigidity, higher top-load crush strength, and the ability to down-weight by up to 20%,” he says. “For example, when thermoforming occurs at low temperatures, cups take on a white appearance that dramatically lowers the amount of white pigment that is required. Beta nucleation also facilitates the production of low density oriented microporous films without the need for a cavitating filler to obtain the void cavities.” Beta nucleation can be used in a variety of
applications to improve properties such as impact strength, drawability, thermoformability, and creep rupture performance in pressure pipes, for example. The drawing characteristics of the beta crystal phase results in more uniform wall thickness distribution in thermoformed PP and biaxially oriented geogrids, allowing for improved down- weighting and cost savings.
Terminology: Nucleator or clarifier?
Nucleators and clarifiers both do broadly the same thing in that they encourage crystallisation of the polymer. This can result in significant improvement in physical properties such as strength and stiffness, heat deflection temperature (HDT), and dimensional stability. It can also shorten cycle times and allow pro- cessing at lower temperatures, which can lift output and save energy. And, depending on the size of the crystal- lites formed, enhance clarity. Nucleators for PP can be divided into two main types – insoluble and soluble. Insoluble types include talcs, metal oxides and sodium benzoate.
46 COMPOUNDING WORLD | June 2020
They are relatively low cost and function by providing sites in the polymer that initiate crystallisation during cooling, so particle size and dispersion is important for effective functioning.
Soluble nucleators, such as sorbitols and nonitols, work by crystallising faster than the polymer during the cooling phase to form a multitude of initiation points. Clarifiers are best seen as nuclea- tors optimised to improve clarity by forming crystallites smaller than the wavelength of light, resulting in reduced light scattering. A number of sorbitols have been used as clarifiers,
including DBS (dibenzylidene sorbitol), MDBS (methyldibenzylidene sorbitol) and DMBDS (dimethyldiben- zylidene sorbitol). DMBDS in particular provides good clarity, thermal stability and favourable organoleptics. It was established in the market by Milliken under the Millad 3988 name but is now available from other suppliers. Milliken’s NX 8000 product line has now taken over as its premium clarifier. Last year, the company announced a 50% capacity expansion for the product, a move brought forward by two years due to “unprec- edented global demand”.
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IMAGE: SHUTTERSTOCK
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