additives | Surface modifi cation


Akro-Plastic loading comparison results of POM (top left) and PA66 (bottom left) bevel gears show severe tooth damage. The PK alternative (far right) ultimately survived longer, failing at the hub


such as gear shift systems, stabiliser joints, roller shutter devices, furniture slide systems, or speed masters.


Opportunities for polyketone Polyketones (PKs), which were available up until 2000 until Shell Chemical discontinued production, have recently become available again from South Korea’s Hyosung, which started up a 50,000 tonne (110 million lb) commercial plant in June of this year. The company announced plans in August for a second plant expected to start up in 2020. Although PK is limited to tempera- tures under 220°C, it offers an unusual combination of mechanical properties, barrier properties, broad chemi- cal resistance, and low water absorption, in addition to wear resistance. This performance combination gives PK an edge over POM and PA in some applications and several com- pounders, including A. Schulman, Lehmann&Voss, Ensinger, and Akro-Plastic, introduced PK compounds in 2014 and 2015. Early in 2015, PolySource became an authorised distributor for PK in North America. In addition to its previously mentioned property


combination, a further unusual feature of PK is that PK-PK material pairs show much lower wear than other like-paired materials, according to Oliver Frey, head of the compounding department at Ensinger. Although it is a common principle to avoid having like materials in contact for wear applications, it can’t always be avoided, and in such cases PK might present a solution, he says. At the upcoming Compounding World Forum in Philadel- phia (8-9 December) Frey will give a presentation on the properties of tribological materials, different material classes, and the use of PK in these applications. Akro-Plastic reports that in a test of combinations of


materials in gears, PK-PK gears without lubrication lasted longer (91 minutes at 1600 rpm and a maximum torque of 5.5 Nm) than the user’s existing combinations of


50 COMPOUNDING WORLD | November 2015


POM mated with lubricated PA 6.6 (72 minutes) or POM mated with lubricated POM (58 minutes). See Figure 1 on page 46 for full results. According to Thilo Stier, head of sales and innovation


at Akro-Plastic, PK is a sensitive material to compound and is prone to crosslinking if the residence time in the extruder is too long. Akro-Plastic uses a compounding extruder from its sister company Feddem that is specially designed with no kneading blocks. It also uses a die-head design that eliminates dead areas. Extremes in pH can also cause crosslinking, he adds. Stier says that temperature control during compounding is also crucial for PK but that, with care, Akro-Plastic is able to compound up to 60% glass fi bre. Carbon fi bre is desirable for wear applications


because of its combination of lower wear and higher mechanical strength compared to glass fi bres (plus carbon fi bres are lighter in weight). The limiting factor, however, is typically their high cost. Akro-Plastic is currently working with BMW on a process that allows compounding of post-industrial, pre-treated carbon fi bre that is a residual material from BMW’s production process. “Using post-industrial recycle brings the price of carbon fi bre down to only two to three times more than glass fi bre,” says Stier.


Click on the links for more information:  www.polysource.net  www.rtpcompany.com  www.laurelproducts.com  www.solvay.com  www.colloids.com  www.lehvoss.de  www.dyneon.com  www.celanese.com  www.poly-ketone.com (Hyosung)  www.ensinger-online.com  www.akro-plastic.com


www.compoundingworld.com


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