additives | Clarifiers & nucleators


Right: The needle-like


structure of phosphate ester (top)


contrasts with the lathe-like structure of Milliken’s Hyperform HPN-20E nucleator (bottom)


oriented films,” he says. “During the stretching process the beta crystals


transform back to alpha crystals and simultaneously produce micro-voids through a self-cavitation process. This micro-voiding allows for the production of low density microporous films, and even breathable films when biaxial stretching is used,” Jacoby explains. The more uniform stretching of beta crystalline


extruded thermoformable sheet leads to improved uniformity in sidewall thickness distribution, resulting in containers with better rigidity and top load crush strength, Jacoby adds, facilitating lightweighting by as much as 20%. The micro-voids produced during stretching also cause the container to turn white due to light scattering from the voids. For companies wanting to produce white parts, this allows for a dramatic reduction in the loading of white pigment.


certain pigments. Phosphate ester salts remain popular as nucleators,


and development continues in this area, too, says Jacoby. Products such as Adeka’s NA-27 have been shown to allow down-gauging of 7% in certain automo- tive parts while maintaining the required stiffness of the component, leading to significant weight reductions. Jacoby also highlights Mayzo’s MPM 2000 master-


batch, which contains proprietary additives that produce the beta crystalline form of polypropylene rather than the more common alpha form. This has a lower melting point, and parts made using beta nucleation are more ductile. “Perhaps even more interesting is the fact a beta crystalline extruded sheet deforms in a very uniform manner during solid state stretching processes such as the production of thermoformed parts and


Sodium benzoate demand Sodium benzoate continues to be used as a nucleating agent. In fact, one leading supplier, Emerald Perfor- mance Materials, says demand for its product, branded Kalama, continues to increase for this application, citing injection moulded consumer goods as well as blow moulding and thermoforming. “Benzoic acid derivatives are well known for their


strong nucleating ability in PP applications, plus they offer better economy and overall superior value in use than other nucleating agents,” says Hubert Degens, VP of Emerald’s Benzoates and Intermediates business. “The ‘dense’ form of Kalama sodium benzoate is ideal for nucleating applications because it grinds or micronizes well without the handling issues associated with powder forms, taking less energy to micronize than other particle forms of sodium benzoate,” he says. Degens says that with particle size having a major impact on the clarity of the end product, the company


One disadvantage of needle-like nucleating agents such as phosphate ester is their tendency to induce very strong and anisotropic crystalline orientation, particularly in the machine versus the transverse (MD /TD) directions of flat part (left image). This can lead to post-mould warpage. Milliken’s Hyperform HPN-20E particles have a high aspect ratio and orient strongly in the polymer melt (right image). This induces strong crystalline orientation of PP lamellae through the thickness of the part so anisotropic shrinkage is minimised


62 COMPOUNDING WORLD | May 2016 www.compoundingworld.com


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