12/15/2023 0 Comments Peek plastic type“Fatigue” refers to the brittle failure of a material under a repeated cyclic loading. "Creep" refers to a material becoming permanently deformed over an extended period of time when under constant applied stress. PEEK-based carbon fibre composites have specific strength many times that of metals and alloys. PEEK demonstrates excellent strength and stiffness over a wide temperature range. This holds true over wide ranges of pressure, temperature and time. It can resist jet fuel, hydraulic fluids, de-icers and insecticides used in the aerospace industry. PEEK is able to resist the damage that can be inflicted in chemically aggressive operational environments, such as downhole in wells the oil & gas industry, in gears in machinery & automotive applications. PEEK is able to tolerate friction and resist wear in dynamic applications like thrust washers and seal rings. This can make it suitable for use in a wide range of thermally aggressive environments, such as those found in the process industries, in the oil and gas sector and inside the engines and transmissions of millions of vehicles. Tests have shown that VICTREX PEEK polymer has a continuous use temperature of 260☌ (500☏). PEEK does not offer merely two or three properties that mark it as the polymer of choice when high performance is required it has a whole variety of them. Low MW PEEK is less impact-resistant but flows much better in the melt so can make small intricate parts easily. However, high MW polymers are very viscous when molten which can limit their ability to fill small moulds. PEEK with longer chains (high molecular weight or MW) tends to be tougher and more impact-resistant than PEEK with short chains. When we make PEEK, we use a process which controls the length of the chains, or molecular weight. Designing to the needs of the application Compared to metals, PEEK-based materials are very light weight, easily shaped, resistant to corrosion and can have considerably higher specific strength (strength per unit weight). The resulting polymer is widely regarded as one of the highest performing thermoplastics in the world. The regular structure of the repeat unit means that PEEK molecules can partially crystallise, and crystallinity provides a combination of wear, creep, fatigue and chemical resistance – more on this later. The ether groups provide some degree of flexibility, for toughness, and like the aryl and ketone groups are unreactive, so providing resistance to chemical attack. The aryl and ketone groups are fairly rigid and provide stiffness which means good mechanical performance combined with a high melting point. The P comes from the Greek “poly” meaning many, so many EEKs make PEEK. This “repeat unit”, shown in the square brackets above, is replicated many times – on average somewhere between 200-300 times – to make a single PEEK polymer chain. Here’s how the building blocks fit together and thus we get Ether Ether Ketone or EEK: From a chemical point of view, PEEK is a largely linear, semi-crystalline polymer. PEEK itself however – like most thermoplastics – is odourless under normal conditions. Small molecules of this type, like toluene & naphthalene, have distinct odours, hence the name. "Aromatic", usually meaning distinctive or sweet-smelling, may seem a strange word here, but scientists use it to describe some molecules containing or made from ring-like structures (like the aryl building block above). R&D into PAEKs has its origins in the 1960’s but it wasn’t until 1978 that ICI (Imperial Chemical Industries) filed their patent on PEEK which was first commercialised as Victrex PEEK polymer in 1981.
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