Aliphatic Polyketones
Properties
Aliphatic polyketone copolymers are a relatively new class of polymers with many attractive and unique properties. The simplest polyketones are perfectly alternating copolymers of alkenes and carbon monoxide. The most common ketones are terpolymers of ethylene and propylene polymerized with carbon monoxide:
The carbonyl group is fairly electronegative and draws electrons away from the adjacent carbon atoms. This leads to strong intermolecular attractive interaction between neighboring polymer chains. For this reason, the melting point and heat of fusion of polyketones is much higher than those of corresponding aliphatic polymers. For example, polyethylene has a melting point in the range of 115 to 140°C whereas poly(ethylene ketone) melts at about 255 ± 5°C.
Polyketones exhibit many desirable mechanical and thermo-physical properties which no other polymer has in this combination. For example, polyketones have high tensile and impact strength, exceptionally high abrasion resistance with minimal wear and tear and very good tribological properties. Other interesting properties include excellent hydrolysis resistance, very low water absorption, high barrier properties against fuel and oxygen, and outstanding chemical resistance. In fact, only very polar (exotic) solvents such as hexafluoro-isopropanol dissolve polyketones.
Polyketones are relative easy to produce and the raw materials such as ethylene, propylene and carbon monoxide are quite cheap; we, therefore, expect the price to come down to less than two dollars per pound. This makes this plastic an inexpensive attractive alternative to many other high performance engineering plastics.
COMMERCIAL POLYKETONES
Shell was the first company to produce aliphatic polyketones under the trade name Carilon. It stopped, however, the production of these resins in 2000 due to low demand. Having failed to find a buyer for their patented technology, they donated it to the US research institute SRI International. In 2014, after ten years of research and development, the South Korean industrial conglomerate Hyosung commercialized a new line of aliphatic polyketones using the former Shell patent. We expect the demand for this new plastic to steadily grow.
APPLICATIONS
Polyketones are very versatile engineering plastics. Due to their excellent mechanical and tribological properties they are an excellent choice for gear wheels, bearings, bushings and other mechanical parts that have to withstand large stresses. This material competes directly with other (lower cost) engineering plastics like POM and polyamides. In combination with these materials almost wear-free gears can be designed. Polyketones are suitable for significantly higher power transmissions than gears made of materials typically used for this application (POM).
Another important property of polyketone is its high barrier properties for many low-molecular weight media such as oxygen or fuel. It is, therefore, an excellent choice for fuel lines. In some cases, it is possible to replace a multiple layer fuel line consisting of PA 12 and PVDF with a single-layer fuel line of this material.
Polyketones are available as high to medium flow resins with high impact resistance. The typical continuous service temperature is in the range of 120°C. Parts made of this resin can be produced with outstanding reproducibility of dimensions and tolerances.
1Hyosung's production of polyketone resins reached 50,000 tons/yr in 2015. Source: K.D. Fedderson Ueberseegesellschaft mbH