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LAB COMPOUNDERS | MACHINERY


operation to be achieved. He says operation will be enhanced with a simplified and intuitive control system that will be aimed specifically at the needs of researchers and laboratory personal. A compact plug and play system will also support integrated equipment, such as HC units, discharge unit and pelletiser, and optionally including premixer and dosing system. The Thermo Scientific Process 11 parallel twin


screw extruder is a bench-top model intended for laboratory compounding and masterbatch devel- opment. It offers a throughput of up to 2.5 kg/h and can produce samples of as little as 20g. The 11mm diameter 40 LD screws offer a torque of 6 Nm and maximum speed of 1,000 rpm. The company recently added a sheet take-off to the range of accessories for the machine, allowing direct production of sample materials. The com- pany says Process 11 results scale well to its larger compounding models, which include the Eurolab 16 XL and TSE 24 MC.


Single screw options


While most lab compounding is carried out on twin screw units, or perhaps internal mixers, there is a role for single screw extruders in producing high quality development compounds, argues Keith Luker, President of Randcastle Extrusion Systems. “This depends on the application, but there is now good evidence to support this,” he says. “Labora- tory single screw compounding has advanced and is slowly moving into production. In addition, small batch mixers are known to be an order of magni- tude better than conventional batch mixers. In terms of laboratories, small batch mixers have downsized - a single pellet can now be mixed. This means that exotic, often otherwise prohibitively expensive materials, can be mixed. Structurally, the technology for single screw mixing is the same for the batch mixers. This is important for scale-up.” One area that Luker believes offers potential benefits in laboratory compounding is three-di- mensional mixing. “Mixing is best advanced towards uniformity by stretching and folding. Orderly mixing requires an understanding of what is being stretched and the order of stretching. Mixing in all three dimensions is required in order to get effective, distributive mixing. Mixing in all three dimensions is not linear but exponential - to the cube - so it is vastly better than mixing in one (linear) direction,” he says. “Historically, single screw extruders have been


poor mixers using shear, melt separation and recombination. Meanwhile, twins have used chaotic elongation for mixing which made them far


www.compoundingworld.com


Right: The Process 11 twin screw extruder from Thermo Scientific is designed for R&D applications


superior for both distribution and dispersion to the single screw extruder. Single screw mixing can now be both elongationally dominant and orderly. The combination can yield results that are superior to twin screws for distributive mixing,” Luker says. “Polymers are viscous and they behave in an


orderly way. By eliminating chaos from the mixing process, a single screw extruder can mix three dimensionally in an ordered fashion. This distribu- tion has inherent advantages over the chaotic mixing inherently present within the twin screw extruder,” he claims. “We continue to make advances in 3D com- pounding through the Randcastle 3D Elongator. The 3D mixing technology increases mixing performance while maintaining the natural advan- tages of the single screw — high, stable pressures at low cost,” he says. “There are many extruder mixing applications that require distribution rather than dispersion and self-wiping — the two main assets that a co-rotating twin screw has over a single. These include polymer alloying, fine mixing of immiscible polymer blends, mixing free flowing particulates, mixing of nano-scale objects, and mixing of plasticisers.”


CLICK ON THE LINKS FOR MORE INFORMATION: � www.coperion.com � www.entek.com � www.kraussmaffeiberstorff.com � www.leistritz.com � www.drcollin.dewww.farrel-pomini.com � www.busscorp.com � www.thermofisher.com � www.randcastle.com


December 2018 | COMPOUNDING WORLD 25


PHOTO: THERMO SCIENTIFIC


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