Application of compressed carbon dioxide in the incorporation of additives into polymers

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Abstract
It has been found that carbon dioxide remarkably accelerates the absorption of many low molecular weight additives into a number of glassy polymers. This effect is due to the high diffusivity, solubility, and plasticizing action of compressed CO2 in polymers. The transport of CO2 and the effects of CO2 pressure on the transport of other low molecular weight compounds in polymers have been studied by a simple gravimetric method: Polymer film samples were contacted in a pressure vessel with compressed CO2, or with CO2 plus various organic liquids or solids, and the sample weight was followed with a fast‐response electronic balance during subsequent desorption at atmospheric pressure. Upon release of the pressure, absorbed CO2 rapidly diffuses from the polymer, while the other compounds desorb much more slowly. The amount of additive absorbed can be determined from the plateau weight of the sample after most of the CO2 has escaped. Extensive kinetic and equilibrium data are reported for the model system poly(vinyl chloride)/dimethyl phthalate/CO2, and a number of other examples of CO2‐assisted additive absorption are given. This “infusion” process, in effect, amounts to the partitioning of the additive between the CO2‐ and polymer‐rich phases; consequently, the relative solubility of the additive in CO2 and in the polymer is a major factor governing the amount of additive absorbed. Data reported here illustrate the generality and potentially broad applicability of CO2‐assisted polymer impregnation.

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