PAMAM Dendrimer Modified Microporous PVDF Membranes for Protein Separation

Abstract

In this PhD thesis, the process of protein separation using PAMAM dendrimer-modified PVDF membranes was systematically studied. By selecting different KOH alkaline solutions, PAMAM was immobilized either on the surface of the PVDF membrane (treated with KOH aqueous solution) or simultaneously on both the surface and inside the pores of the PVDF membrane (treated with KOH isopropanol solution). The effects of different alkaline treatments on the surface properties of PVDF membranes and on the filtration of whey protein and casein were also systematically investigated. Additionally, the Donnan-steric pore model with dielectric exclusion (DSPM-DE) was used to analyze the separation processes of PVDF membranes and PAMAM dendrimer modified membranes. The study on PAMAM dendrimer modified PVDF membranes revealed that immobilizing PAMAM on both the surface and inside the pores of PVDF membranes significantly enhanced the rejection of whey protein but notably reduced the permeate flux. After immobilizing generation 3 PAMAM dendrimer, with carboxyl functional groups, the rejection for whey protein increased from 58.9% (PVDF membrane) to 98.8%, while the permeate flux decreased from 15.3 LMH (PVDF membrane) to 2.3 LMH. When the PAMAM dendrimer was immobilized only on the surface of the PVDF membrane, both the rejection for whey protein and permeate flux increased. After immobilizing generation 3 PAMAM dendrimer, with carboxyl functional groups, on the membrane surface, the rejection and permeate flux for whey protein increased to 79.0% and 30.3 LMH, respectively. Simultaneously modifying the membrane surface and interior results in decreased bulk porosity and increased Donnan potential, leading to a significant increase in whey protein rejection. However, the smaller bulk porosity also causes a decrease in the permeate flux. Modifying only the membrane surface increases the pore size and generates a negative Donnan potential. This modification results in both higher whey protein rejection and permeate flux. However, due to the larger pore size, weaker Donnan potential, and the absence of charges within the pores (resulting in a weaker dielectric exclusion), the whey protein rejection of surface modified membranes is lower than that of membranes modified on both the surface and interior.