materials | Polyketones
Right: PK offers high
resistance to automotive fuels, espe-
cially the new bio-diesel and ethanol grades
mately ten times better than PA11 and PA12. In addition, PK can resist acids that can form from sulphur-containing biodiesel fuels; these are a big problem in POM and also in PA. In addition, PK is lower in cost than PA11 and PA12.” Watkins predicts that aftermarket fuel-pump applications will finish validation tests before the end of the year, although OEM parts will take longer to commercialise.
Above: High operating temperatures and chemical resistance makes PK a candidate for structural under-hood components
Consistent mechanical properties A key benefit of PK for a variety of applications is that its mechanical properties withstand a broad range of temperatures and humidities in use. Building and construction applications can benefit from this broad performance range, for example. “Testing is currently underway with glass-filled PK as a potential replacement for glass-filled nylon in window and door hardware, because the nylon tends to lose its toughness properties in regions such as the southwestern United States, where there is low humidity and broad temperature swings from very hot to cold,” says Watkins. PK’s toughness is demonstrated by high values for notched Charpy, elongation, and tear strength. This toughness, combined with its low moisture absorption and excellent chemical resistance, makes PK better than resins such as PBT, POM, or some nylons in various building applications. A legacy Shell application that will benefit from PK’s
return is in commercial beverage dispensers for frozen drinks. “The alternate material (POM) has poorer toughness at low temperatures and so has had a higher rate of failure at -30°F,” explains Watkins, who is working with a major OEM to qualify PK and anticipates it to see commercial use in Q1 of this year. PK has approval for EU direct food contact, and an
FDA food contact notification was published in January 2016. US National Sanitation Foundation (NSF) approvals for drinking water are expected by the end of March. PK also shows advantages in commercial
beverage dispensers for hot drinks. “PK can be used in flow
tubes, for example. PK can replace housing lids that are currently made from PC/ABS, but are cracking because
of inadequate chemical resistance,” says Watkins. “The combination of PK’s glossy surface appearance and exceptional chemical resistance is ideal at resolving the poor resistance of PC/ABS to disinfectant cleaners, oily foods and sanitizers.” Toughness in a range of temperatures and humidi- ties is also a potential benefit in electrical and elec- tronic applications. “PK can be compounded with flame retardant additives and it is easy flow, so complicated parts with thin walls can be moulded,” says Watkins. He notes that PK is competitive with LCP and PPS from a processing standpoint (for example, for thin wall connectors), although PK has a lower use temperature than LCP and PPS. Usage temperatures of PK are currently being evaluated, but a relative thermal index (RTI) of approximately 130 °C is expected. PK’s high resilience is demonstrated in its high
elongation at yield (25%), and it can be subjected to larger, cyclic deformations than many other engineer- ing thermoplastics, making it useful in electrical connectors, according to Veith. PK is also ductile over a broad temperature range, with elongation at break of approximately 300% at 23 °C. In automotive interior applications, PK offers high
resilience combined with low volatile organic com- pounds (VOC); this is an advantage over POM, which can have problematic emissions from the final part due to formaldehyde content, says Thomas Collet, global product and marketing manager for the Customized Polymer Materials business unit at Lehmann & Voss.
Tribological applications Polyketones are said to be uniquely suited for tribologi- cal applications because of their wear resistance, combined with other properties, such as chemical resistance or fatigue resistance. In particular, PK-PK pairs have lower wear than other like-paired materials (see Nov. 2015 article). At the Compounding World Forum (held in Philadel- phia in the US on 8-9 December last year), Oliver Frey, head of the compounding department at Ensinger, presented data showing the tribological properties of
18 COMPOUNDING WORLD | March 2016
www.compoundingworld.com
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