MACHINERY | ALTERNATIVE COMPOUNDERS
reduced sensitivity to any foreign materials that may be incorporated in feedstocks. Last year, Korean bio-products group CJ Bio conducted research comparing the Farrel Continu- ous Mixer with a twin-screw extruder for processing bioplastic formulations including PHB, PHA and talc, and PHB, PLA and talc under a variety of conditions. The research concluded that the Farrel Continuous Mixer processed both formulas with lower specific energy resulting in enhanced molecular weight retention, lower melt index and higher impact strength than a comparably sized twin-screw extruder.
IMAGE: FARREL POMINI
Above: A CPeX Laboratory Compact Processor (right) and CP550
continuous mixer in Farrel Pomini’s
development lab
continuous mixing technology is inherently well suited to the processing of biopolymers and recyclates, for example, because they require low processing temperatures, short residence times and efficient shear mixing,” he says. “Biopolymer and recycled material applications
are also temperature sensitive, subject to molecular weight degradation. Over 70% of customer demonstration trials in both our US and UK facilities are currently within this landscape and include PLA, PHA and wood fibre/cellulose,” says Lloyd. “Farrel Continuous Mixers offer efficient and uniform mixing shear, in combination with lower processing temperatures and residence time, effectively reducing molecular degradation. The one large feed port offered by the continuous mixer lends itself to the irregularly shaped material that is often seen with recycled feedstock.” Compounding recycled plastic materials is a
complex process because recyclates are intrinsi- cally contaminated, partially degraded, and contain different pigments and granule sizes that make processing challenging. Lloyd says Continuous Mixers offer some advantages for compounders of recycled materials, including the large single-entry feed port that is capable of ingesting irregularly sized feedstocks as well as large volumes of additives and fillers. Large rotor tip to wall clear- ances and mixing chamber volume also allow for efficient processing at controlled temperatures, increased material flow, high filler levels and
The concave feed flight design in Farrel Pomini’s new High Dispersion Rotor increases conveying efficiency of lower bulk density materials
64 COMPOUNDING WORLD | October 2023
www.compoundingworld.com Lloyd says the company is also seeing significantly
increased activity in traditional markets such as PVC flooring compounds and decking products. “PVC is extremely temperature sensitive and Farrel Continu- ous Mixers excel at processing heat sensitive material because of its short residence time, low processing temperatures and efficient rotor shear, which imparts less energy and therefore temperature into the polymer. Our equipment also has multiple tempera- ture controls zones and rotor cooling.” Energy reduction is important from two perspec-
tives, Lloyd explains. “Firstly, with escalated energy costs, it is important to be energy efficient to maintain profitability. Secondly, it is often important to impart less specific energy into the polymer to minimise heat history and maintain molecular structure.” Continuous mixing technology is based on two
counter-rotating, non-intermeshing rotors and a large free volume mixing chamber. The large mixing chamber allows for liberal material circula- tion and good distributive mixing, while the specialised rotor geometry facilitates efficient levels of shear and good dispersive mixing. The standard 6 L/D rotor provides a short residence time and a low heat history for the polymer, while still providing a high-quality homogeneous mixture at the exit of the processor. With a single-entry feed port, materials are fed into the mixer separately or as a pre-blend while liquids can be injected directly into the mixing chamber. This straightforward feeding method eliminates the need for side feeders. Continuous mixing technology also utilises atmospheric
IMAGE: FARREL POMINI
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