Resistance of Polymers to Permeation by Air Conditioning Refrigerants and Water

The permeability of several polymers to refrigerants and to water vapor has been determined. The investigation included refrigerant R-12 which is currently used in automotive air conditioning and refrigerants R-22 and R-134A which are considered as future candidates. For the different polymers investigated, the permeability constants for R-22 at 93°C ranged between 0 and cm/11×10−10 cm2 sec cm2 cm Hg for the plastics, 29×10−10 and 124×10−10 for thermoplastic elastomers and 135×10−10 and 276×10−10 for crosslinked elastomers. The permeability decreased with decrease in test temperature and with increase in molecular size of the refrigerants. Hence both R-12 and R-134A exhibited lower permeability constants than R-22 because of their bigger size. Trends in water permeability of the different polymers were mostly opposite to those of the refrigerant permeability. For example, polynorbornene has the lowest water permeability of the polymers tested, but has one of the highest permeability constants for refrigerants. Of the new polymers investigated, the lowest overall permeability to water and refrigerants was exhibited by PET polyester, polypropylene, Hytrel polyester, and plasticized Polyamide 12 (5% plasticizer).