Three papers are availsble on the system cellulose acetate—carbon dioxide.1-3 In all the cases the degree of esterification
and the origin of the samples were the same: CA obtained from Eastman Kodak Co. contained 39.8% of acetyl groups. Stem and De Meringo1 studied sorption of CO2 in
CA at 273—343 K and reported the dual mode sorption parameters for somewhat narrower range of temperature. In a subsequent paper2 of the same group the reported isotherm
at 303 K was confirmed, but no sorption parameters were given. Sada et al.3 studied the sorption in the temperature range 293—313 K. The table summarizes the sorption
parameters found in Refs. 1 and 3 for this system. It can be seen that there is a reasonable agreement for Henry's law solubility coefficient kD, but not for other two model
parameters. The C'H and b values reported in both papers monotonously decrease with temperature, but there is a significant discrepancy between two sets of values.
From the temperature dependence of kD and S it was found, respectively, log(S/(cm3
(STP)cm3 atm-1)) = -3.8226 + 1438.7/(T/K) log(kD /(cm3(STP)cm3 atm-1))
= -3.9595 + 1236.3/(T/K)
ΔHD = —23.7 ± 1.8 kJ/mol
ΔHs = —27.5 ± 2.3 kJ/mol.
It it difficult to give much credit to the parameters reported in any of these works. Nevertheless, as one may tentatively suspsct the effects of exposing the polymer
to high pressure of CO2 as a main reason for these differences, the data of Sada et al.3 should be regarded as describing the sample 'as received,'while those of Stern
and De Meringo1 as characterizing the polymer swollen in high pressure gas. Much larger values of the Langmuir capacity parameter C'H are typical for such samples.
The temperature dependencies of S and kD are shown in Figures 67 and
68