materials | Polyketones
extent with other polymers. We believe that traces of contamination cause degradation in PK,” says Frey. Similarly, moulding and extrusion of PK must be
carried out carefully. For example, an injection-mould- ing machine barrel must be sized properly to avoid a long residence time, warns Watkins. “If residence time is too long, the PK may start to darken (although POM has a similar issue),” he says. “Because PK crystallises quickly, you can reduce moulding cycle times compared to POM or PBT but, if you’re not careful, PK can freeze at the moulding nozzle. There is a learning curve, but PK is relatively trouble-free once you optimise equip- ment to run it.” Hyosung has established an internal task force to
Above: PK offers the flow required in thin wall connectors
PK compounds. He noted that PK’s benefits are unique in applications that require mechanical or tribological properties in combination with low water absorption and chemical resistance. Akro-Plastic offers its normal flow and easy-flowing
Akrotek PK grades formulated to meet various needs. These incorporate glass reinforcements, carbon-fibre reinforcements and flame retardants. At the upcoming Compounding World Congress (Cologne, Germany, 18-20 April 2016), Thilo Stier, sales director and innovation manager at Akro-Plastic GmbH, will be presenting “The return of polyketones: developing new compounds and applications including long-fibre grades and tribological components.”
Compound with care There are some difficulties to consider when com- pounding PK polymers. “The biggest issue when compounding PK is avoiding thermal oxidation of the polymer due to dead spots or cessation of flow in the processing equipment. If you keep the polymer moving, you can process it satisfactorily,” reports Veith. H “Have every piece of ancillary equipment up and running at steady-state and turn on the PK feed as the last item in the start-up checklist, then get to steady state as fast as you can. If you must go down due to a mechanical failure elsewhere, purge out the PK first, then solve the mechanical problem. Pay special attention to the restart, and look out for gels and degradation products in the extrudate or processed polymer. If you have these defects and they don’t clear up in short times, then shut down and clean out the equipment and try again tomorrow,” he advises. Ensinger’s experience with compounding PK highlights the importance of handling it on very clean equipment. “We observed a negative impact on mechan- ical properties when the equipment was not cleaned absolutely carefully, which is usually not needed to that
20 COMPOUNDING WORLD | March 2016
improve properties and processing stability as quickly as possible, including evaluating better stabilization additive packages, as it sees this as a critical area for improvement. The company says it is collaborating with a number of partner companies to enhance long-term thermal stability, UV resistance, and processibility using different approaches in polymerisation, additive packages, and alloy technologies. In general, the resin is compatible with a wide range
of fibre reinforcements, fillers, colorants, and additives, such as flame retardants, thermally and electrically conductive additives, wear-resistance additives, and others. In addition to unfilled grades, Hyosung offers a 30% glass-filled, flame-retardant grade and an unfilled, flame-retardant grade. Compounders offer many combinations.
Right: The good wear performance of PK could lead to applications in appliance bushings and
bearing rings
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