**2.2.3 Plasma treatment and plasma-induced grafting polymerization**

The same as other methods mentioned above, few study was reported on the modification of PES hollow fiber membranes by plasma treatment or plasma-induced grafting method. Only one study on the modification of PES hollow fibres by O2 plasma treatment (Batsch et al., 2005) was reported. After about one month of stable operation, the membrane samples were taken and also cleaned with chemical solutions, and the fouling could be prevented by the modification.

### **2.2.4 Thermal-induced grafting and immobilization**

Thermal induced graft polymerization is a facile way to modify PES membranes. The method always uses chemical initiator or cleavage agent. Furthermore, many kinds of biomolecules, such as enzyme, protein and amino acid, could be covalently immobilized onto PES membranes by a simple chemical reaction.

Kroll et al. (Kroll et al., 2007) chemically modified commercially available PES and PSF hollow fiber membranes by reacting terminal hydroxyl groups with ethylene glycol diglycidyl ether (EGDGE) to produce terminal epoxy groups. For increasing loading capacity hydroxyethyl cellulose polymers were bound to the epoxy groups. Second epoxidation produced final polymers containing reactive epoxy groups on the hollow fiber surface. From this modified PES and PSF, respectively, a wide variety of N-containing reagents (e.g. iminodiacetic acid (IDA)) can be bound to the epoxy groups. The different reactions were proved by acid orange II assay and phenol sulfuric assay. The chelating IDAmembranes were complexed with different divalent metal ions (Cu2+, Ni2+, Co2+, and Zn2+). Immobilized metal ion affinity PES hollow fiber membranes were used for purification of a recombinant protein (GFP-His) from Escherichia coli, which carried a polyhistidine sequence.
