YRayinduced modification

Y-Ray-induced graft polymerization has been used extensively because it is the most versatile and promising one due to its rapid formation of active sites on the substrate surface and in the material matrix. Almost all of the polymeric materials can be modified by y-ray with different monomers and the resulting material is highly pure as no initiator or related impurities remain in the matrix. However, as a very high energy radiation, y-rays have a tremendous penetrability such that active sites are also generated in the material bulk, which often affects the inherent bulk properties.

Table 3. Characteristics and bovine serum albumin (BSA) permeation properties of 2-hy-droxyethyl methacrylate (HEMA)-grafted PPMMs with different grafting degrees (PHm)

Sample code

Jw Js

Rme

Resistance (1014m-1)

Rtf Rcg

Wettability11 (cos e)

BSAj

(^g/cm2)

PPa

77.1 24.2

4.67

14.8

10.1

-0.32

-36.47

104.5

PH1

2.9

75.2 26.9

4.78

13.4

8.60

-0.15

-31.33

83.6

PH2

7.2

69.9 27.8

5.15

12.9

7.75

0.03

-29.10

69.4

PH3

12.5

68.6 28.7

5.28

12.5

7.22

0.27

-26.72

38.1

PH4

24.0

68.1 37.6

5.43

9.57

4.14

0.31

-11.57

20.9

PH5

32.2

66.3 43.6

5.64

8.25

2.61

0.44

-7.75

26.9

PH6

40.6

60.9 44.8

5.91

8.03

2.12

0.56

-5.22

9.0

a PPMM with exposure of Y-rays b Degree of grafting (wt %) = (wg - w0)/w0 x 100, where w0 and Wg are the weights of the membrane before and after the grafting reaction, respectively c Deionized water flux d Flux of 1 g/l BSA in 10 mM PBS of pH 7.4 at 23 ± 2 °C

e The membrane resistance (Rm) was calculated by the measured deionized water flux f The total resistance (Rt) during the filtration of protein solution was calculated by the flux

(Js) of BSA protein solution g Rc caused by BSA protein in solution was calculated by subtracting Rm from Rt h The average estimated error for cose was ±0.04 1 The average estimated error was ±9%

j Irreversible adsorptive fouling of the membrane was defined as the amount of BSA absorbed onto the surface of the membrane after chemical cleaning

Kang et al. (2001) used Co60 as a y-ray source for surface modification on the PPMMs by graft polymerization of 2-hydroxyethyl methacrylate (HEMA). Through adjusting the radiation dose, modified PPMMs with different grafting degrees were prepared. Protein adsorption measurements were carried out on these membranes by filtration of BSA solution through the membranes. The results are shown in Table 3 and Fig. 11. The flux of deionized water decreased with increases in the grafting degree of polyHEMA (PHEMA). On the other hand, the flux of BSA buffer solution increased with increasing PHEMA grafting degree. Clearly, the more hy-drophilic the surface (increasing cosd value), the lower the flux decline with

10 30

Degree of grafting(wt%) Fig. 11. Buffer flux as a function of the 2-hydroxyethyl methacrylate (HEMA) grafting degree

10 30

Degree of grafting(wt%) Fig. 11. Buffer flux as a function of the 2-hydroxyethyl methacrylate (HEMA) grafting degree

Fig. 12. Schematic illustration of ozone-induced graft polymerization

BSA buffer solution. The decrease of flux of the deionized water could be explained by narrowed or plugged pores as a result of the swelling of grafted PHEMA in a buffer solution. In the case of the permeation of BSA buffer solution, although the pores narrowed with increasing PHEMA grafting degree, the increased flux of the PHEMA-grafted membranes was due to the weakening of hydrophobic interaction between the BSA molecules and the hydrophilic membrane surface. Therefore, the flux of BSA buffer solution increased because the fouling caused by the adsorption of BSA was reduced with increasing PHEMA grafting degree.

Fig. 13. a Amount of protein adsorbed per unit area of the virgin PPMM, grafted (ozone treated for 1, 3, and 5 min) and the commercial modified GVHP (hydrophobic) and GVWP (hydrophilic) membranes. b Fluxes for virgin and modified membranes during BSA solution permeation

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