PEI, polyetherimide, ULTEM™, compatibility, thermoplastics
The compressor industry faces a difficult design environment for achieving performance improvement, reduced cost, and lower environmental footprint. In order to address some of these challenges, thermoplastics can be considered as a replacement for metal in some compressor parts. Thermoplastics have been found to be suitable for steel replacement in structural parts for automotive and brass replacement in water-handling applications such as meters. As such, we believe certain high-performance engineering thermoplastics might be suitable candidates for metal replacement in various compressor parts. Herein, several commercial thermoplastic resins were tested for chemical compatibility to common compressor lubricants and two standard refrigerants. Chemical compatibility tests were completed under conditions comparable to those observed within compressors, inclusive of high temperature, high pressure, extended exposure time, and combinations thereof. Of the thermoplastics tested, unfilled ULTEM™ resin (PEI or polyetherimide) was found to outperform competitive resins in terms of resistance to chemical attack by POE lubricants, R134a and R410A refrigerants. The protocol included visual inspection for color shift as well as the measurement of tensile strength retention for exposed parts. Gas chromatography mass spectrometry (GC MS) was also utilized to determine if low molecular weight species leached out of ULTEM resin during exposure to POE oils. No species were detectable with molecular weight under 1000 g/mol. Chemical resistance screening is ongoing for glass filled thermoplastic offsets and additional validation testing is planned.