Surface Modification of Membranes for Fouling Reduction

Despite great effort that has been made to reduce and understand fouling, this phenomenon is still a major problem in membrane applications. Numerous methods, both from a chemical and engineering point of view, have been introduced to overcome this problem. In this contribution, we report on the modification of membranes with polyelectrolytes and polyelectrolyte multilayers utilizing two of the mentioned strategies. The effect of surface modification on the fouling behavior as well as on the critical flux will be discussed on two examples, microfiltration membranes and RO membranes

Ultrafiltration membranes based on PES-PEG block copolymers

Although subject to research for decades, fouling is still one of the major limiting factors in membrane applications. Numerous methods have been suggested to overcome this shortcoming, like crossflow filtration, backflushing, air sparging, all of them in combination with chemical cleaning. However many of these techniques imply off-production cycles, resulting in lower yield, shorter lifetime of membranes and therefore higher costs. Another approach to reduce fouling involves the modification of membranes with charged and / or hydrophilic polymers. These are either added to the casting solution or subsequently grafted onto the membrane surface. However, both methods have their specific drawbacks. Adding hydrophilic polymers to the dope solution leads to a significant loss during membrane preparation step (coagulation). On the other hand graft modification involves most often several steps and bears the risk of damaging (degrading) the membrane material resulting in loss of mechanical stability. In this work we report on UF membranes prepared from poly(ether sulfone)-poly(ethylene glycol) block copolymers with poly(ethylene glycols) of molecular weights varying from 200 g/mol to 4000 g/mol but constant molar fraction of 5 mol%. Furthermore, block copolymers with increasing content of PEG-200 up to 20 mol% were prepared. This approach has the advantage over surface modification that the degree of functionalization can be easily controlled by the monomer composition. UF-membranes from block copolymers were prepared by conventional NIPS process using NMP as solvent and water as non-solvent. The effect co-monomer type (molecular weight of PEG) and co-monomer concentration on the morphology of the resulting membranes (Figure 1) as well as their filtration properties including protein fouling will be discussed in detail. Please click Additional Files below to see the full abstract

Ribonucleoparticle-independent transport of proteins into mammalian microsomes

There are at least two different mechanisms for the transport of secretory proteins into the mammalian endoplasmic reticulum. Both mechanisms depend on the presence of a signal peptide on the respective precursor protein and involve a signal peptide receptor on the cis-side and signal peptidase on the trans-side of the membrane. Furthermore, both mechanisms involve a membrane component with a cytoplasmically exposed sulfhydryl. The decisive feature of the precursor protein with respect to which of the two mechanisms is used is the chain length of the polypeptide. The critical size seems to be around 70 amino acid residues (including the signal peptide). The one mechanism is used by precursor proteins larger than about 70 amino acid residues and involves two cytosolic ribonucleoparticles and their receptors on the microsomal surface. The other one is used by small precursor proteins and relies on the mature part within the precursor molecule and a cytosolic ATPase