materials feature | Additives for polyolefins
Antifog additives
reduce surface tension to turn condensed
droplets into a thin continuous film
efficiently extracted in the vacuum degassing process. The additive, which is typically used at a dosage of
0.5 to 2% in PP, effectively works as a stripping agent reducing VOCs by more than 80% compared to extrusion without vacuum. For best results, high screw speeds and temperatures are applied to reduce the viscosity and improve degassing. A single degassing zone is used at the end of the extrusion processes with a good vacuum, ideally below 50 mbar. The extruder screw configuration should include a reverse flow segment in front of the degassing zone.
Fighting fogging A very different type of anti-fogging effect is required in packaging applications. Here additives are used to prevent the formation of water droplets on the inside of films – they can also be useful for agricultural films. Danisco has developed chemically-modified fatty acids that work as efficient anti-fogging solutions for both PE and PP. The company’s senior application manager Bjarne
interior applications, developing new additives for reducing odour and fogging levels. Jörg Garlinsky presented the company’s new BYK-P 4200 additive which he said provides highly effective removal of odours and VOCs (volatile organic compounds) without the negative influence on mechanical and optical properties that can be associated with existing zeolite and charcoal based adsorber technologies. Garlinsky explained that BYK-P 4200 works in two
steps. During extrusion, the PP carrier releases the active additive which forms a micro-foam under the raised temperature and shear stress. In this process, the volatile organic compounds and odour components are wetted. Downstream in the extruder, the microfoam collapses and these unwanted components are
Nielsen explained that the additives have a tailored polarity to control migration, and they work by reducing the surface tension at the water/polymer interface. The condensed water forms a thin continuous film and there is no loss of transparency. Danisco’s Grindsted PGE O 80 is recommended for PE film applications, offering good antifog performance in both the short and long term at relatively low loading levels. Nielsen presented data showing that 0.2% of the additive in a 50 micron blown LDPE film was still effective after more than 400 days. If the antifog additive is to be used in a complex
multilayer construction, then it needs to be added to several layers, because the sealing layer where it has to be active may only be 5-8 microns thick. Nielsen added that laminated multi-layer films and metallocene LLDPE require very efficient antifogs and that Danisco’s Grind- sted PGE 308 grade works well in such structures.
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