materials feature | Additives for polyolefins
allows the use of more complex mould designs. daan Vanwynsberghe of Milliken discussed the
historical development of nucleation technology leading up to what he described as “hyper nucleation” with the company’s latest Hyperform Hpn-20E and Hpn-600ei additives. The former is particularly suited to thin-wall injection-moulded packaging and pipe extrusion applications, giving balanced physical properties, low level efficacy and high productivity. it can also be used for pigment levelling in caps and closures plus other injection moulded parts. Hpn-600ie is used in thermoforming applications to
SEM Plastik is using PP containing Milliken Hyperform HPN-600ei to thermoform these milk- shake cups for a global fast- food company
Property and processing improvements leo nijhof of AkzoNobel discussed the application of organic peroxides in polyethylene. They can be used for a variety of purposes at different stages of pE production and processing. peroxides act as an initiator for free radical polymerization of ethylene in ldpE production. They are also used in polymer modification, for example as viscosity modifiers through molecular weight broadening or for grafting functional groups. in com- pounding and processing they can be used for gelation or increasing viscosity to facilitate foaming processes. And of course peroxides are widely used in cross-linking pE for applications such as cables and pipes. nijhof said that on-going developments in the power
cable, pEX-a pipe/tubing and cross-linked rotomoulding markets are creating opportunities for alternative peroxides. He said that more and more producers of medium-voltage (mV) power distribution cables are producing compounds in-house rather than buying in ready-made products. He stressed that in such cases, the cable producers should apply “clean room” working conditions and go for easy-to-handle and easy-to-dose peroxide and antidegradant additives, preferably in a liquid form. one example is Akzonobel’s Trigonox T, which is a tert-butyl cumyl peroxide. For cross-linked pEX-a pipes, nijhof highlighted the
advantages of a single-step screw extrusion process using infra red curing compared to ram-extrusion with pipe heating. However, the former’s open cure technol- ogy demands a more safe peroxide, such as Trigonox 145 instead of Trigonox B. For rotomoulding applications, a peroxide with very high thermal stability, such as Trigonox 311, facilitates the melt flow behaviour. This gives more freedom in polymer selection, makes particle size less critical and
22 compounding world | January 2012
give an improved quality/output ratio along with excellent aesthetics and optimised use of resources. one company that has recently taken advantage of these benefits is SEm plastik, a leading Turkish sheet extrusion and thermoforming company. it is using pp containing Hyperform Hpn-600ei to produce milkshake cups for a global fast-food company and is targeting an annual production of around 6.5 million cups. SEm says that using the new grade has enabled it to cut the weight of the cup by close to 10% with no loss of mechanical properties. dr oleg Kulikow of the Universität Der Bundeswehr
Munchen presented the results of research work into fluorine-free processing additives for extrusion. These have greater adhesive properties to metal than molten polyolefins and form a lining at the die surface during extrusion to help prevent shark-skin effects. Hydropho- bic materials like fluoropolymers are often used as lubricants, however in natural joints the lubricant is hydrophilic. dr Kulikow proposed a new ppA comprising polyethylene glycol and silanol, which he said is friendly to environment and cheap to produce.
Fire fighting one inherent property of polyolefins is that they burn well with high heat capacity; therefore flame retardants are important for some products and applications. Thor has developed its new Aflammit pco halogen-free flame retardants for polyolefin films and thin-wall parts. Jérôme de Boysère explained how the new products, which are based on organic phosphorus chemistry, address some of the weaknesses of existing Fr systems for polyolefins. They have good synergistic effects with nor HAlS
structures, such as BASF’s Flamestab nor 116, and tests were carried out with Aflammit pco and nor 116 at a ratio of 9:1. Various factors affect the loading required, including the mFi, film thickness, and the presence of fillers, particularly carbon black and titanium dioxide. According to de Boysère, Aflammit pco gives similar
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