Release kinetics of low molecular weight solutes from mixed cellulose ethers hydrogels: a critical experimental study

Release kinetics in water of five low molecular weight model solutes (urea, cyclohexanone, acetaminophen, phenacetin, cafein) from mixed cellulose ether hydrogels have been investigated between 20°C and 60°C. Three different divinylsulfone crosslinked networks, showing acceptable mechanical resistance and variable temperature sensitivity (in terms of water swelling) have been studied. The solute molecular weight (ranging between 60 and 200×10−3 kg mol−1) does not seem to play a crucial role for the diffusion coefficient variation. Network shrinking induced by a temperature increase results in a slight temperature dependency for diffusion coefficients. Data interpretation has not been attempted through mechanistic diffusion models, given the complex structure of mixed cellulose esters gels. The only approach which leads to an approximate description is based on the free volume model developed by Yasuda et al. According to this model, network density is shown to be the main explicating factor of the effective diffusion coefficient variation.