MACHINERY | ALTERNATIVE COMPOUNDERS


plumbing. Like the Baker’s Transformation, they are only better mixed in two dimensions. That is their fundamental flaw because what is wanted is better mixing in three dimensions,” Luker argues. “Our dynamic multiplicative mixer has a multiplier of 100. Treated like a two-dimensional static mixer, its seven mixing elements make 100 trillion layers (1007


). As a three-dimensional mixer acting on


Figure 1: A schematic representation showing the basic principle of the Bakers’ Transformation in melt mixing Source: Randcastle Extrusion Systems


venting, eliminating the need for additional vacuum systems. Recent developments include a new rotor with a concave feed flight design. The High Dispersion Rotor increases conveying efficiency at the infeed of the mixer, aiding intake of lower bulk density materials. It is well suited to applications requiring high dispersion such as processing fibre grade, high colour carbon black and colour concentrates. Farrel Pomini is also working with FPInnovations,


a Canadian non-profit Research and Technology Organisation, on biocomposite applications. Togeth- er with wood products producer West Fraser and bio-based products manufacturer Good Natured Products, the companies are developing engineer- ing bio-based alternatives to traditional plastics. biocomposites. Central to the research is the integration of various products from West Fraser operations into biopolymer blends to create 100% bio-based and compostable compounds. US-based single-screw systems maker Randcastle Extrusion Systems has developed a new option for compounding applications. “It is in a class that I call ‘multiplicative mixers’, of which there are two kinds - static and dynamic,” says Keith Luker, Chief Execu- tive Officer. “This new single screw compounder is a dynamic, multiplicative mixer, known as the Molecu- lar Homogenizer.” Static multiplicative devices emulate the Baker’s


Transformation (Figure 1), he says, and the most common is the twisted ribbon which has a multi- plier of two (meaning that it doubles the layers with every twist). After eight twists, it makes 256 layers (28


is a static device used to make layered film and sheet. They also have a multiplier of two and as many as 4,096 layers (212


) are known. “Conceptually, static multiplicative mixers are 66 COMPOUNDING WORLD | October 2023


polymer chains, it mixes and homogenises at the polymer molecular level.” Luker says that the essence of the static mixer is its simplicity. Once installed, it does its job. Opera- tors do not need to take it apart to reassemble parts to make it work better, he says, it works the same, no matter how the mix changes. He says that the dynamic multiplicative mixer shares this advantage — it does not require taking apart and reassembling with other expensive parts on shafts. Randcastle claims the Molecular Homogenizer


overcomes some of the drawbacks of static mixers — it does not use pressure to convey the mix, so output is not compromised, and it is dispersive in three dimensions. It also has an advantage over twin screw extruders in that the entire flow is processed through the sequential mixing zones, so all is mixed the same. Luker believes that the Molecular Homogenizer


can replace twin-screw extruders in many applica- tions. “It is simple to operate, produces a more uniform mixture and is far less expensive.” Preliminary experiments carried out by the company show significantly slowed water vapour absorption in PMMA, from hours to over three days. “Potentially, we may be able to influence water absorption for other hygroscopic materials and that could reduce the amount of drying necessary for hygroscopic materials.” Luker adds that that single screw venting, as


represented by the conventional two stage screw, is not especially good but says there are many elongational flows in the Molecular Homogenizer that can all be accessed by a single vent process- ing at zero pressure. These constantly remix the flow and expose new, stretching surfaces that greatly enhance bubble break-up and gas release.


). The second device is the layer multiplier, which


CLICK ON THE LINKS FOR MORE INFORMATION: � www.aimplas.net � www.linkedin.com/in/hans-ulrich-siegenthaler � www.irap.heia-fr.ch � www.busscorp.com � www.cpmextrusiongroup.com � www.farrel-pomini.com � www.fpinnovations.ca � www.randcastletechnology.com


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