ADDITIVES | FUNCTIONAL FILLERS
Mechanical properties – 15% filler content
automotive, both physical and chemical foaming are being more widely used to achieve lightweight- ing targets, but he says final properties are strongly determined by the dimension of the gas bubbles and their distribution in the thermoplastic resin. IMI Fabi says its NSultraC talc exhibits a stronger nucleating effect than standard fine talcs in foaming applications and provides opportunities for high quality unpainted surfaces.
Figure 2: Effect of coating on impact strength of a 15% filled PC/ABS compound (ratio 65/35) Source: Imerys
dimensional stability in plastics. However, enhanced reinforcement can result in reduced impact resist- ance of the finished product. Berjeaud says that, thanks to a surface coating developed specifically for this application, Luzenac R7C from Imerys provides good stiffness/impact balance and limits interaction with the PC matrix (Figure 2). The 10-micron top-cut talc grade is available in white and grey versions, so is suited to all types of finished applications where it provides the mechan- ical performance and good cost effectiveness. “In addition to mechanical performance, talc also improves char cohesion and limits heat transfer by barrier effect. In many cases, engineer- ing thermoplastics contain a flame-retardant package; Luzenac R7C physically contributes to improving the fire performance of the compound,” says Berjeaud. IMI Fabi has developed a new talc product
Right: IMI Fabi has developed new perfor- mance talcs for automotive applications such as TPO compounds
portfolio specifically for plastic automotive applica- tions. Designed for modification of thermoplastic olefins (TPOs), the new products include highly engineered grades for lightweighting and surface coated grades designed to improve final appear- ance of plastic compounds. HVTextra, for example, has been developed to achieve extremely high stiffness in PP/TPO at a lower filler loading in order to minimise the specific gravity of the compound. It is recommended for TPO compounds containing up to 20% by weight of talc (more typically in the range of 5-15%). The material also helps in reducing the thermal expansion and mould shrinkage of the compound while its plate-like structure helps reduce warpage. It is also available in a compacted format, which makes it easier to feed than other traditional highly micronised talc grades. Product and Application Development Manager
Piergiovanni Ercoli Malacari says the company has also been targeting foamed polymer parts. In
58 COMPOUNDING WORLD | August 2018
www.compoundingworld.com
PEEK performance Moving up the pyramid of ETPs, polymers such as PEEK and PEKK are known for their outstanding thermal and mechanical properties. Aside from the high processing temperatures – typically in excess of 375°C – when these polymers are combined with fillers and fibre reinforcements their viscosity can increase to a point where torque, temperature, and pressure demands can approach the limits of some processing equipment. “A common approach to reducing viscosity is to
decrease the molecular weight of the polymer, or to use bimodal molecular weight distributions which, while allowable for some uses, can decrease mechanical performance,” says Joe Lichtenhan, President of Hybrid Plastics, which produces POSS (Polyhedral Oligomeric Silsesquioxane) additives. “The high processing temperatures of PEEK and PEKK also limit the use of traditional plasticisers due to their propensity to degrade and volatilise during compounding.”
Lichtenhan says POSS is becoming a “go-to additive solution” for precisely such complex compounding scenarios. “Favourably, POSS cages bearing all-phenyl groups – such as dodecaphenyl – melt and are thermally stable in the 400°C tem- perature range. When phenyl POSS cages contain silanols (such as the heptaphenyl trisilanol) they also behave as high temperature dispersants which both reduce viscosity and aid in dispersion,” he says. All-phenyl containing POSS are white-solid
PHOTO: SHUTTERSTOCK
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