Study of water vapor sorption by cellulose esters with different degrees of substitution

In this research, the sorption of water vapor (WV) by various cellulose esters with different degrees of substitution (SD) has been studied. It was found that if the sorption value is measured in moles of H2O per mole of repeating units of the esters, then sorption properties depend only on the degree of substitution and not on the type of substituent. The lowest sorption is observed for triesters due to the absence of hydroxyl groups, which have the greatest contribution to the sorption process. To describe sorption isotherms, a calculating equation A = Ao(1- K lnφ)-1 was derived, where Ao is the maximum sorption value at relative vapor pressure φ=1, and K is the coefficient. This equation allows adequately describing experimental S-shaped sorption isotherms of WV for various esters having different SD. It was shown that the most probable sorption mechanism is the binding of polar water molecules by polar groups of various esters.