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High-temperature compounding | processing feature


The growing use of high-performance polymers presents many challenges to compounders as processing temperatures soar to 400˚


C and beyond. Jennifer Markarian reports


Compounding heats up


There is growing interest in very high performance plastics, typically for the replacement of metals in ever more challenging applications. Polymers such as polyetheretherketone (PEEK), polyetherimide (PEI) and polysulphone (PSU) are being specifi ed in critical components to withstand extreme conditions in the electronics, medical, automotive and chemical process- ing sectors, for example. Incorporating the required reinforcements, additives


and colorants into these high-temperature polymers presents signifi cant challenges to compounders. High-temperature compounding is more demanding in every aspect. It has implications for the extruder design and its materials of construction, as well as requiring tighter process control, more precise pelletizing, careful compound formulating, and a rigorous approach to cleaning and maintenance.


Equipment design The basic challenge of compounding polymers with very


high melting points, such as those listed in Table 1, is getting the extra heat into the polymer to melt and mix it, and subsequently removing the heat to cool and pelletize the material. Techniques to meet these challenges include using


high-wattage heaters, improved insulation, effi cient cooling systems, and designs with good heat transfer. In addition, temperature sensors must be designed to measure high-temperature ranges. Standard grades of PEEK, for example, require a minimum processing temperature of about 400°C (750°F), notes Richard Leibfried, market development manager for Victrex Polymer Solutions. The company’s higher-temperature versions of PEEK (HT and ST grades) require a minimum capacity of 430°C (800°F). Leibfried recommends ceramic heating bands and notes that the insulation of bare metal helps dramatically. Twin-screw extruders are generally used, and longer


length/diameter (L/D) ratios are typically employed to enable adequate melting and mixing. Longer extruder


Table 1 - Typical melting points of high-performance polymers Resin


Polysulphone (PSU) Polyetherimide (PEI)


Polyethersulphone (PES) Polyphenylene sulphide (PPS)


High-temperature nylon (HTN) or polyphthalamide (PPA) Polyetheretherketone (PEEK) Liquid crystal polymer (LCP) Source: Solvay Specialty Polymers


www.compoundingworld.com Amorphous resin


glass transition temp (°C) 190 215 220 - - - -


Crystalline resin melting point (°C)


- - -


285


300-330 (depending on grade) 345


325-400 (depending on grade) December 2012 | COMPOUNDING WORLD 13


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