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additives | Functional fillers


Right: LKAB Minerals’ UltraCarb


hydromagne- site huntite in rock and


powder form


some key compounding issues. It was this need that led to the project with Leistritz. “Fillers are becoming more and more functional,” says Michael Thummert, head of Corporate Communi- cations at Leistritz. “New coatings and other surface chemistries are a tremendous advantage for final applications and further facilitate higher filling levels.” Viering explains that he sees two main technical


trends at present – high quality fillers with greater func- tionality along with improved polymers able to incorpo- rate an increased filler content. “We believe that providing functional fillers with metallic characteristics and anisotropy for better utilisation of the polymer filled volumes is becoming very important,” he says. “For example, hydromagesite huntite is an efficient halogen- free flame retardant filler, which provides good endothermic fire retardancy and char formation. However, it does require compounding and conversion processes that are well adjusted. High filler content requires stable, high volumetric dosing. It is also often observed that die heads are not particularly well designed to handle highly filled compounds.” Thummert says that the key concept for good


Below:


Compounds incorporating LKAB’s UltraCarb filler are used in wire and cable applications


incorporation of a high degree of fillers in the polymer matrix is volume. “The more volume the machinery provides, the easier the handling will be. If this is combined with compounding equipment providing high torque levels, then this is extremely helpful in process- ing highly viscous materials. High filler content also means a lot of air is inserted in the process, which makes venting and degassing a challenging task for processors. This means that the screw geometries have to be adapted to this task, in addition to the high dispersion needs of the highly filled compound formula- tions. In particular, in order to meet the compounding requirements of UltraCarb LH3C, the improved design of the side feeders in terms of functionality with segmented screws, high volume and better handling was extremely helpful,” he says.


Surface treatments New treatment technologies are also being developed that allow existing fillers to deliver improved functional- ity. One company working in this area is Hybrid Plastics – the developer of POSS additives. “The trend is for multifunctional fillers that, in addition to providing filler effects such as reinforcement, adding volume and providing cost reductions, can also provide other enhancements including dispersion, fire retardancy, clarity and anti-scratch effects,” says Joe Lichtenhan, the company’s President. “Multifunctionality can simplify formulations, reduce formulation SKU count, and provide differentiation in the market place.” Hybrid Plastics says that POSS – Polyhedral Oligomeric Silsesquioxane – is a nanostructured product that bridges the gap between ceramic and organic materials. POSS can improve product perfor- mance without sacrificing mechanical properties and is used in a range of industries. The company adds that POSS technology is derived from a continually evolving class of compounds closely related to silicones through both composition and a shared system of nomenclature. POSS chemical technology has two specific features.


Firstly, a chemical composition that is a hybrid, interme- diate (RSiO1.5


) between that of silica (SiO2 (R2 ) and silicone SiO). Secondly, POSS molecules are physically large


with respect to polymer dimensions and nearly equiva- lent in size to most polymer segments and coils. “POSS silanols - SO1458, SO1450 and SO1455 - are our primary surface treatment products,” explains Lichtenhan. “For thermoplastics, the POSS is com- pounded into a resin at the feeder throat with pellets, while the filler is b-staged. However, for pre-treatment of powders POSS is dissolved in solvent and/or sprayed onto powders and tumble mixed. Silanols are chemi- cally unique and a bit rare, but POSS silanols are chemically stable. Silanols react to surfaces in a similar fashion to coupling agents. The POSS silanols bind to polar surfaces of powders or key ingredients and ultimately form a Si-O-Metal bond on the surface. No ethanol, methanol or acetate is eliminated, with the


20 COMPOUNDING WORLD | August 2016 www.compoundingworld.com


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