Wang et al. (2000) performed surface modification of PPMMs by using ozone to introduce peroxide onto the membrane surface. After that, graft polymerization of HEMA was carried out. The polymerization was initiated at a mild temperature by redox decomposition of the peroxide (Fig. 12). Similar to the results of Kang et al. (see previous section), these HEMA-grafted PPMMs also showed great protein resistance (see Figs. 13a,b and 14). The trend of flux decline for the modified (grafted) membrane was nearly the same as that of the unmodified (virgin) membrane. However, the flux recovery efficiency (Fig. 14), which is closely associated with the reversibility of membrane fouling layers, increased markedly with increasing ozone-treatment time by up to 5 min. It appears that membrane fouling might be the result of accumulation of protein aggregates at the membrane surface regardless of the membranes used (grafted or not), but could be reversed more easily for the grafted membranes with an appropriate time of ozonation. This can be attributed to the more hydrophilic nature of the modified membrane surfaces. Also, the steric hindrance resulting from the grafted PHEMA chains may play an important role in preventing the direct interaction between the membrane surfaces and proteins.
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