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PPS COMPOUNDS | MATERIALS


Once an exotic novelty, PPS is now a versatile and widely available high performance polymer.Peter Mapleston looks at the history and explores the latest developments


PPS – an established novelty


Not so long ago, polyphenylene sulphide (PPS) ranked among the most exotic polymers around. One company made it in the beginning – Phillips Petroleum – and it was used for specialty coatings rather than plastics as its molecular weight was rather low. Phillips then made a version with higher molecular weight through a process of thermal cross-linking, found that it had excellent heat and chemical resistance and could be injection moulded. It named it Ryton. Today, few suppliers of engineering thermoplastics does not have a PPS grade in its portfolio. The semi-crystalline polymer comes in numerous guises – crosslinked (branched) and linear – and there are new and more sustainable ways to make it. As a result, there are all sorts of compounds available based on PPS. These are almost always compounded with a fibre reinforcement or a mineral filler but now include flexible as well as rigid grades. PPS compounds provide an excellent complement to polyamides for applications requiring greater heat resistance — it has a melting point of approximately 280°C. The resin is also inherently flame resistant and


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mechanically strong (although brittleness can present a problem with some types). Branched PPS polymer exhibits high rigidity under elevated temperature conditions and displays some novel benefits in regard to resistance to creep deformation. Linear PPS, meanwhile, offers better elongation and impact resistance. It is less prone to absorbing moisture under high heat and humidity conditions compared to the crosslinked polymer. Due to its low ionic impurities, linear PPS is a very good choice for fuel cell parts and other applications that demand strict electrical characteristics. Linear PPS also tends to be whiter in colour. Applications for PPS continue to grow, many in automotive, electrical/electronics, aerospace, and chemical engineering, but increasingly also in other sectors such as medical and the water industry. It is used in injection moulding, extrusion, and in fibre production. In comparison with mainstream engineering plastics such as polyamides, volumes are relatively modest but growth is very healthy. Global PPS volumes stood at around 100,000 tonnes in 2016.


Main image: Automotive water pumps are a target application for PPS, exploiting its good temperature resistance and dimensional stability


� April 2019 | COMPOUNDING WORLD 27


PHOTO: POLYPLASTICS


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