MACHINERY | ALTERNATIVE COMPOUNDERS
Alternative solutions for changing needs
Alternative compounding systems can play a key part in ensuring that compounders can take on the challenges of high energy costs, material shortages, and the sustain- ability goals of the circular economy, according to compounding expert Hans-Ulrich Siegenthaler. A specialist compounding consult- ant who spent several years at machinery maker Buss, Siegenthaler has, since the beginning of this year, held the post of professor for the Compounding & Extrusion research
axis of the iRAP Plastics Institute at the University of Applied Sciences (HES-SO) in Fribourg, Switzerland. “In this time of major global challenges such as the energy crisis, climate change and raw material scarcity, key technologies such as compounding in general and alterna- tive compounding technologies in particular, can be a concrete answer to the given challenges. Why? Each of these technologies offers a specific property profile that is key to the corresponding requirements,”
filtration and pelletising. Staying with single-screw machines, US-based
Randcastle Extrusion Systems is a well-known developer of smaller extrusion systems with enhanced mixing performance. The company has patented various compounding technology elements, including The Recirculator and The Elongator, which it says “operate with twin-like performance.” CEO Keith Luker says the company recently filed for another patent on mixing, for a product tentatively known as the Molecular Homogenizer. This can be used as a stand-alone mixing device or attached to the end of a twin-screw extruder to enhance homogenization. “The Molecular Homogenizer uses a novel mixing mechanism that has an orderly structure. It organises materials in three dimensions. Each mixing set is capable of order of magnitude improvements in mixing compared to the standard metering section. The ability to keep water vapour from agglomerat- ing into water implies an unprecedented mixing ability. While it’s early in development, we’ve done some amazing things,” Luker says. “For example, we processed undried hygroscop-
ic materials on our mixing screw, and we can’t see any bubbles. Apparently, the mixing is so good that we’re stopping the water vapour gas from agglom- erating into something we’d normally see as bubbles. So, we’re using water vapour and bubbles as a stand-in for measurement,” he says. Undried hygroscopic materials that Randcastle
has processed without visible bubbles include PMMA, PVA, PC, PEEK and PET. The company has also processed mixtures of hygroscopic materials, such as SAN-based colour concentrates. “SAN is
70 COMPOUNDING WORLD | October 2022
Siegenthaler says. He cites several examples: the use
of CPM Extrusion’s ring extruder to process biopolymer resins and natural fibre reinforcements; development of a new technology by Buss and P&M Cable Consulting to improve energy efficiency in XLPE cable compound insulation; a process for recycling end-of-life wind turbine blades using planetary extruder technolgy from Entex; and recycling of scrap carpet and flooring waste using X-Compound’s kneader extruders.
hygroscopic (absorbent); the pigments in colour concentrates are adsorbent,” says Luker. “When processing 100% colour concentrates into film, we saw no bubble in either black or white.” Experiments with reactive extrusion have includ- ed work with PVA, which is hygroscopic. “When mixed with 3% reactive agent it converted about 0.37% of the polymer into a gas. Yet we saw no bubbles.” No sign of bubbles was also reported in tests involving LDPE with coffee chaff, which is hygroscopic and contains oils that become gaseous. Another hygroscopic polymer, PMMA, has also been tested on the system. “We dried it before we put it into our new mixing screw. We pelletised it and left the pellets exposed to the air. Normally, after four or five hours, you’d see bubbles in the extrudate. After three days we processed the PMMA in a conventional single screw and we saw no bubbles,” he says. “The last thing a polymer reactor does is pelletise dry material. As in the PMMA example, we hope to decrease the water absorption rate to the 30 to 60 day range so that no drying, or far less drying, will be necessary. The energy savings potential is enormous,” he claims. Luker also sees potential for the technology in
improving twin screw extrudates. “Better distribu- tive mixing will add to the quality of what twins can produce with a single heat history,” he says.
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.farrel-pomini.com �
www.busscorp.com �
www.cpmextrusiongroup.com �
www.gneuss.com �
www.randcastletechnology.com
www.compoundingworld.com
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