TECHNOLOGY | REACTIVE COMPOUNDING
Right: Steer is fine tuning its Omega series extruders for high quality TPV production
and zinc that are usually difficult to disperse in PP. The application with peroxides came about almost by accident, he says. The new masterbatch is said to
provide the same effect as regular peroxide masterbatches at addition rates some 20-25% lower. The pelletised product is claimed to have “exceptional” storage stability: Albee says it will not crystallise or fuse together during shipping or storage, even under extreme warehouse storage conditions.
Crosslinking peroxides Swiss compounder Polycompound is also working with peroxides, but in its case, it is creating polyeth- ylene compounds (filled and unfilled) that are subsequently crosslinked, typically during produc- tion of cable and tubing, using the Sioplas process. This employs a mixture of peroxide and silane to produce a polymer with vinyl silane grafts that is subsequently crosslinked in a separate process once the cable or tube has been extruded. Crosslinking occurs via silane groups grafted onto the PE, with the function of the peroxide being to break the PE chains to provide locations for the grafts. The company also grafts maleic anhydride (MAH) onto polymers (including polyolefins, PVdF, and others). Once again, peroxide is frequently used as the polymer chain opener. Polycompound operates exclusively with
co-kneader technology. Grafted compounds can be produced on twin-screw extruders, but Peter Imhof, Head of Sales at the firm, says co-kneaders provide greater flexibility over where the peroxide, which it normally uses in liquid form, can be injected. It can do this directly into the melt at various positions along the co-kneader extruder using a pump. “This provides us with the control we need over the distribution of the peroxide in the compound,” he says. “We only have a very small temperature window to work in, so this is crucial for a good compound.” Staying below the temperature limits required
with peroxide can be very difficult during a normal compounding operation, Imhof explains. This is why a two-step process is very often used, separat- ing peroxide addition from other compounding steps. However, he says with appropriate equip- ment such as a well-configured co-kneader, it is possible to stay within the limits in a one step process, which enables cost savings to be made. One of the best-known examples of the use of reactive compounding is in production of thermo-
38 COMPOUNDING WORLD | August 2019
plastic vulcanisate (TPV) elastomers, which incorpo- rate partially crosslinked EPDM rubber in a polypro- pylene matrix. However, according to twin-screw extruder producer Steer, achieving good disper- sion of the elastomer in the polypropylene using a twin-screw extruder is not a simple task. “Steer understood this problem faced by several compounders globally and decided to offer an industry solution,” says a company spokesperson. “By deploying its patented FGT technology and know- how, Steer will be able to disperse elastomer in thermoplastic polymer without causing degradation.”
Key challenges The main challenges to overcome, according to the company, are: achieving an optimum dispersion of EPDM and crosslinking agent in the PP; and avoiding the shear peaks that can otherwise cause degradation of the elastomer. In developing its solution, Steer used an Omega 40H Class (L/D 60) lab extruder for R&D trials. It calibrated materials and configured screws specifically for the extruder. “Use of DSA & FKB elements provides gentle dispersive mixing along with elongation mixing of elastomer and cross-linking agents, reducing peak shear without shift in desired properties,” Steer says. “Steer special elements will help in obtaining final uniform pellets without any degradation.”
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.ikt.uni-stuttgart.de/en �
www.ditf.de/en � University of Bayreuth
http://www.polymer-engineering.de/en �
www.coperion.com �
www.jsw.co.jp/en �
www.mmatwo.eu � Addisperse
www.afi-global.com �
www.polycompound.ch �
www.steerworld.com
www.compoundingworld.com
PHOTO: STEER
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