Microstructure relaxation process of polyhexafluoropropylene after swelling in supercritical carbon dioxide

ABSTRACT This paper studies the process of relaxation of a polymer after swelling in supercritical carbon dioxide. Polyhexafluoropropylene (PHFP) was chosen as the object for investigation. The relaxation process was monitored by a change of the permeability coefficients for a number of gases. Thin polymeric films of PHFP were modified by different treatments: drying to a constant weight, annealing at a temperature slightly higher than the glass‐transition temperature, and swelling in supercritical carbon dioxide. The permeability coefficients of six gases, He, H2, O2 N2, CO2, and CH4, were measured after each stage of the treatment. It was shown that the permeability coefficients in the films were increased by 2.4 times for He, 3.6 for H2, 5.9 for O2, 8.1 for N2, 6.7 for CO2, and 10.9 for methane. The permeability coefficients of the same gases were measured 50 days later after swelling in supercritical carbon dioxide. A decrease in the permeability coefficient demonstrated that the relaxation process had taken place. Nevertheless, the values exceeded the initial ones for annealed samples by 2.0 times for He, 2.4 for H2, 1.8 for O2, 1.7 for N2, 1.7 for CO2, and 1.3 for methane. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43105.