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 69 kD, gammaglobulin 159 kD and dextrans 70 and 200 kD, 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 69 kD, while dextrans of mass 70 kD are retained in 30%, and these of mass 200 kD in more than 75%. This depends on the linear structure of dextran particles and their significant polydispersity which was confirmed by the chromatographic analysis.