MACHINERY | ALTERNATIVE COMPOUNDERS
Left: The satellite-
screw configuration of the Gneuss MRS extruder makes it well suited to processing nanoparticle suspensions
post-production waste are produced in different shapes. These include film
edge cuts, regrind from more voluminous backing layers and milling dust. “The recycling of these
materials and returning it into the produc- tion was one of the main ideas in the develop-
ment of X-Compound’s CK225,” he says. The CK225 unit incorporates a kneader screw of 225mm diameter and has been designed to accept all recycling material stream types (both internally and externally recycled materials) and to convert them all into material that can be used for further production of flooring products. “Due to the very gentle mixing principle, a
degradation of the sensitive PVC materials is avoided at high capacities – up to 8,000 kg/h,” Kretschmer says. “The experience shows that the machine is capable to process an extremely broad range of materials. This makes the machine well suited for current and future challenges to produce sustainable floors.” The CK225 first arrived on the market in 2017. Since then X-Compound has delivered some eight lines. “Some of these lines are already used for LVT recycling,” says Kretschmer. “Currently our custom- ers mainly use post-industrial sources while having a view on the market for all kinds of post-consumer sources.”
Nano opportunity The MRS multi-screw devolatilising extruder from Gneuss was also developed to rival twin-screw equipment. Available in various sizes, it was originally aimed at reprocessing post-consumer and industrial PET waste without the need for pre-drying. Close to 40 units are now being used for this application around the world and a handful of units are processing other polymers. Since its introduction, however, the company has seen opportunities in other diverse applications and nanocomposites is one of them. Incorporating fillers with at least one dimension under 100nm – nanofillers – into polymer melts is not a task for the faint-hearted. The powders
82 COMPOUNDING WORLD | October 2019
frequently contain agglomerates that need to be broken up and handling requires more extensive safety measures than are used with “regular” powders. One of the reasons for using nanofillers is the much higher surface area-to-volume (SA:V) ratios than regular fillers, but that advantage is not fully realised if there is a high proportion of agglomer- ates – something that does happen frequently. Gneuss says that after six years of development work, it can now offer an industrial scale process that allows the introduction of nanofillers into polymers, without agglomerates and with “com- pletely safe handling” of the nanoparticles. Gneuss Nano Compounding Technology makes
use of the company’s MRS extruder in combination with a twin-screw extruder. Gneuss says nanoparti- cles are extremely difficult to integrate into com- pounds using conventional technologies. “They stick together like crazy” is how Gneuss Executive Andrew Prangnell puts it. So the best way to mix them into a polymer melt is by introducing them, not in powder form, but as an aqueous dispersion. Creating dispersions of nanoparticles such as carbon nanotubes is already a well-established practice. “The particles are contained safely in the suspension and cannot get into the environment,” the company says.
Managing dispersion It is not simply a matter of pouring the dispersion into a hopper, however. In the Gneuss equipment the dispersion is introduced into the melt via a special injection and mixing chamber part-way down a purpose-built twin extruder, which oper- ates at very high pressure of around 100 bar. The extruder is manufactured by a third-party company and the quality of the dispersion achieved using it is said to be very good. This compound then passes directly to the MRS, which drives the water out of the melt. The MRS is extremely effective at this because its configuration of eight satellite screws rotating around a central screw means the water is provided with a much greater melt surface to escape from than is available in either single- or twin-screw extruders. In addition, the MRS provides useful secondary distributive mixing. The version of the MRS used for this application
is different from “standard” units as it is taking a polymer melt rather than a solid, so the feed zone does not need to be as long. The extruder is designed so that, with a mixture of at least 70% polymer and suspension, the liquid holding the nanoparticles in suspension is removed within five
www.compoundingworld.com
PHOTO: GNEUSS
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