The effect of seasoning a membrane-forming solution on the separation properties of chitosan membranes

The ability to retain high-molecular substances is a basic criterion of membrane applicability in the process of ultrafiltration. Separation of high-molecular compounds on flat chitosan membranes was investigated. Membranes were produced by the wet phase inversion method, immediately after preparing the solution and then seasoning for a month. Prior to membrane formation, the change of rheological properties of membrane-forming solutions was determined. Prior to membrane formation, rheological properties of membrane-forming solutions were determined immediately after preparing the solution and after a month seasoning. Testing substances were model proteins: albumin 69kD, gammaglobulin 159kD and dextrans 70 and 200kD, as well as a real system - 1% skim milk solution. The ability to retain proteins was determined by a standard method which consisted in the determination of retention coefficient. Protein concentration was determined by a spectrophotometric method. Dextran separation was determined by the standard method which covered determination of dextran concentration by coulometric titration, and - because of the linear structure of particles and their polydispersity - by gel chromatography through the analysis of molecular weight distribution in the feed and permeate. Practically, chitosan membranes retain proteins above 69kD, while dextrans of mass 70kD are retained in 30%, and these of mass 200kD in more than 75%. This depends on the linear structure of dextran particles and their significant polydispersity which was confirmed by the chromatographic analysis.