Surface modification of engineering plastics through swelling in supercritical carbon dioxide

In order to improve the tribological characteristics of polymer materials, the authors tried to impregnate the surface of engineering plastics with the lubricating oil by using supercritical carbon dioxide. The oil impregnation ratio on crystalline polymer was influenced by both the glass transition temperature (T_g) and the degree of crystallinity. In case of using the polymer possessing lower T_g with large difference between the T_g and treatment temperature, the higher impregnation ratio was obtained, and the crystallite in crystalline polymer prevented the impregnation of lubricating oil. The results of polarized optical microscopic observations and FT-IR spectroscopy studies indicated that the lubricating oil was preferentially impregnated to the amorphous region in crystalline polymer, and the high-concentration layer of lubricating oil having the thickness of ca. 30 um was formed at the vicinity of surface area. The result obtained in this study, which reports the preferential lubricating oil impregnation to the surface of crystalline polymer under supercritical carbon dioxide, suggests that the tribological characteristics of crystalline polymer would be improved by applying this oil impregnation method without sacrificing the bulk mechanical strength.