Low‐pressure CO2 sorption in poly(vinyl benzoate) conditioned to high‐pressure CO2

Abstract

AbstractSorption of CO2 in poly(vinyl benzoate) was gravimetrically measured at pressures up to 1 atm. Sorption isotherms were determined above and below the glass transition temperature Tg from 5 to 85°C. The isotherms were analyzed by the dual‐mode sorption model assuming that the plasticizing effect of sorbed CO2 is negligible at this pressure range. The solubilities and Henry's law dissolution parameters were compared with those obtained by the high‐pressure sorption and permeation measurements. Henry's law dissolution parameters were in good agreement with one another. However, the solubilities first determined here were smaller than those determined by the high‐pressure sorption experiment at the same temperature. It was clear that the Langmuir capacity of the present specimen was smaller in spite of similar high‐pressure CO2 exposure. Relaxation of the polymer was expected to be one of the reasons. This expectation was confirmed from the observation and analysis of sorption isotherms after two kinds of treatments. After annealing above Tg, the Langmuir capacity was shown to be decreased to 1/2 or even to 1/3 from the sorption isotherms below 45°C. This means that the conditioning to the high‐pressure CO2 surely has a large effect on the nature of glassy polymer. Just after high‐pressure CO2 exposure at 25°C, increased solubility was observed. Furthermore, the slow decrease of solubility, that is, the decrease of conditioning effect, was also followed from the continual measurements at 25°C. This result reflects not only the characteristic of sorption capacity after high‐pressure CO2 exposure, but also the relaxation of polymer in glassy state.