ABSTRACT
Even for hydrophobic polymers, the diffusion of solutes is, in general, affected by thermodynamics and kinetics of water uptake.
Guo (21) described the effects of water on the properties of ethylcellulose films. The change of density, morphology, porosity, and drug transport properties of ethylcellulose films with the water content in the polymer solutions were investigated. Because of the strong hydrogen-bonding property of water, the process of dissolving and mixing of ethylcellulose in a solvent (ethanol) was dramatically changed when a nonsolvent (water) was added in this system. As the solubility parameter difference between water and the rest of the components and the evaporating rate difference between ethanol and water could cause the phase separation of polymer solution during the film-forming process, the porosity of ethylcellulose films
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0.8
0.6
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0.2
increased with water content in the polymer solutions. The film density and the drug permeability of ethylcellulose films decreased and increased with water content in the polymer solutions, respectively; and these results were very consistent with the porosity increase of the ethylcellulose films (21).
