(512c) Phase and Interfacial Behaviour of Aqueous-Two Phase Systems Based on Hyperbranched Polymers

Extraction which is based on the miscibility gap of aqueous two phase systems (ATPS) is a principal possibility to concentrate proteins. These systems are composed by adequate polymers, salts. The fundamental idea of this work was the extension of the material base by the application of hyperbranched polyesteramid in combination with dextran to form an ATPS. The characteristics of this ATPS were compared with a classical ATPS composed of PEG8000 and dextran. In contrast to linear polymers hyperbranched polymers with different functional groups and different architectures which influence the thermodynamic behaviour and the miscibility gap can be synthesized. A further advantage of hyperbranched polymers in fluid separation is the low viscosity compared to linear polymers. In both ATPS the partitioning of L-serin on the two coexisting phases was experimentally investigated. In addition to the experimental analysis, both ATPS were modelled using the Lattice Cluster Theory (LCT) combined with Wertheim Association theory. The LCT was used to take especially the branched architecture of the polymers into account. By the incorporation of the Wertheim theory, the influence of polar interactions is considered. With help of the binary phase behaviour of PEG 8000 + water and of HB + water the binary interaction parameters of the used model were determined. With the introduced model both ATPS were calculated in good agreement with experimental data. The partitioning behavior of L-serine was also experimentally and theoretically investigated in both ATPS’s in order to compare the extraction performance. To obtain interaction parameters for L-serine the solubility of L-serine was investigated in water and aqueous polymer solutions; whereas the experimental data for the solubility in water. Because of a miscibility gap, the solubility of L-serine could not be estimated in hyperbranched polyesteramide containing solutions. For that reason, binodal curve was estimated and the model was fitted to this liquid-liquid equilibrium. With the thermodynamic model, the partitioning coefficient for L-serine was calculated in both ATPS’s in good agreement with experimental data.

Next to phase equilibria calculations also the interfacial properties of polymeric ATPS were calculated. To calculate the interfacial properties of polymeric ATPS the density gradient theory (DGT) was used in combination with the developed thermodynamic model. The DGT allows the calculation of interfacial tension as well as of mass transfer across the interface. At first, the DGT was used to calculate the interfacial tension of investigated ATPS. By the use of one parameter fitted on one experimental data point, the interfacial tension was calculated in good agreement with experimental data. Moreover, the concentration profile across the interface was calculated. It can be stated, that the polymers are not accumulated at the interface. Based on this calculation the DGT was used to calculate the mass transfer across the interface. At first the system ATPS PEG8000+ dextran T40 + water was experimentally and theoretically investigated. The experiments were conducted in a Nitsch-cell for two tie lines. By the DGT the mass transfer across the interface could be modelled by adjusting the mobility coefficient of each component pair in one experiment. This mobility coefficient could be used to predict mass transfer in this ATPS for the other tie line in good agreement of experimental data. Based on the mobility coefficients estimated for Dextran and PEG, the mass transfer in the quaternary system PEG8000 + dextran T40 + L-Serine + water was examined. It can be stated, that the mass transfer in this system can be modelled with the DGT combined with the developed thermodynamic model. But it has to be considered, that L-Serine is accumulates at the interface, when the experiment starts. Next to this system also the mass transfer in the system HB + dextran T40 + L-serine + water was examined. It can be stated, the mass transfer in this system can be modelled with DGT combined with LCT+Wertheim.