Free Volume and Water Sorption by Cellulose Esters

The results ofthe sorption properties of cellulose acetate (CA) with different degrees of substitution (SD) are summarised. It has been shown that the sorption capacity of CA in water vapour decreases naturally with increasing content of acetate groups in monomeric units of cellulose ethers. The experimental isotherms are analysed according to the double sorption model. Hydrate numbers of hydroxyl and acetate groups were determined. The paired parameters of the Flory–Huggins interaction were calculated. It is shown that the decrease of the Langmuir component is due to the replacement of hydroxyl groups by ester groups, whose local sorption capacity by water vapour is lower than the sorption capacity of OH groups. In the area of high humidity, there is an increase in vacancy sizes due to plasticisation of the sorbents.