1 The effect of filling on water uptake has been studied for coatings based on aqueous dispersion Acronal-290D and pigment part consisting of titanium dioxide and calcium carbonate. It was found that an increase in the pigment volume concentration is accompanied by an increase in the rate of water absorption, but the maximum value of water uptake is characterized by a minimum near the critical pigment volume concentration. It was shown that at a low degree of filling of the films, water absorption is a long-term process, the kinetics of which can be described by superposition of two functions that take into account both the Fickian character of water diffusion and the relaxation process, associated with structural changes in the samples.

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SYNOPSISIt 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 COP in polymers. The transport of CO, and the effects of CO, 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 CO,, or with COP 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 CO, 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 CO, has escaped. Extensive kinetic and equilibrium data are reported for the model system poly (vinyl chloride)/dimethyl phthalate/CO,, and a number of other examples of C0,-assisted additive absorption are given. This "infusion" process, in effect, amounts to the partitioning of the additive between the COz-and polymerrich phases; consequently, the relative solubility of the additive in CO, 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 C0,-assisted polymer impregnation.

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