22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Grafting of PVDF membranes with TMA/SA mixed-charge copolymers by
atmospheric-pressure plasma for anti-biofouling applications
T.C. Wei and H.L. Shih
Department of Chemical Engineering and R&D Center for Membrane Technology, Chung Yuan Christian University,
Chung-Li, Taiwan
Abstract: PVDF membranes were coated with 2-[(methacryloyloxy) ethyl] trimethylammonium
chloride (TMA) and 3-Sulforpopyl methacrylate potassium salt (SA) monomers, then undergone
plasma induced graft-polymerization. By varying the initial monomer ratios, the final membrane
surface charge could be controlled to regulate the interactions with biofoulants from waters or
blood – proteins, bacteria, blood cells, and lead to a low-biofouling surface.
Keywords: Plasma modification, biomimetic material, zwitterionic polymer, anti-fouling
1. Introduction
Membrane technology is important in wastewater
treatment and bioseparation applications. However,
biofouling arising from protein adsorption and biofilm
formation are of great concern because of significant
reduction in utilization and increase in operational cost.
The cell membrane can prevent the adsorption of proteins
in the blood stream owing to the zwitterionic
characteristic of the phospholipid molecules on cell
membranes. Thus, it is of great interest to synthesize
pseudo-zwitterionic polymeric membranes to reduce
protein adsorption in bioseparation processes. In this
study, a novel Glow Dielectric Barrier Discharge (GDBD)
plasma was used to graft 2-[(methacryloyloxy) ethyl]
trimethylammonium chloride (TMA) and 3-Sulforpopyl
methacrylate potassium salt (SA) onto poly(vinylidene
fluoride) (PVDF) membrane. The functional groups of
two monomers TMA and SA are of positive N+(CH 3 ) 3
and negative SO 3 -. As schemed in Fig. 1, the membrane
surface charge could be controlled by varying the initial
monomer ratio. The interactions between biofoulants
(proteins, bacteria, blood cells) and membranes of
different surface charge were investigated. A low
biofouling PVDF membrane with good charge balance in
the mixed-charge TMA/SA copolymer was found.
2. Experimental
As sketched in Fig. 2, PVDF membrane coated with
TMA and SA monomers of 3 mg/cm2 was placed inside
atmospheric-pressure plasma discharge to induce graftpolymerization. The plasma reactor consists of two quartz
plates of 10 cm in width, covered with copper electrodes
of 7 cm in width. Helium plasma of 30 slm flowrate was
generated by 13.56 MHz RF power of 100 W. The
treatment time was 60 s. After plasma induced grafting,
the mixed-charge PVDF membranes were extracted with
isopropanol for 90 min in the ultrasonic device to strip off
homopolymers and unreacted monomers. Finally,
membranes were dried for 24 hours in a vacuum oven
under reduced pressure to remove residual solvent.
The chemical structure and surface morphology of the
modified PVDF membranes were characterized by FTIRATR, XPS, SEM and Laser Scanning Confocal
Microscope (CLSM). The anti-biofouling capability of
prepared membranes was characterized by the protein
adsorption of bovine serum albumin (BSA) and lysozyme
(LY). In addition, human blood cells and E.Coli were also
carried out for investigating attachment ability of
membranes. Lastly, cyclic filtration test was conducted in
BSA solution for bioseparation application.
Fig. 2. Schematics of plasma induce graft-polymerization.
3. Results and Discussion
Fig. 1. Scheme of research concept.
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Fig.3 shows the effect of monomer ratio on the grafting
density. The grafting density exceeds 0.41 mg/cm2 for
samples with TMA:SA ratio of 2:1 after plasma grafting.
As the SA content is increased, the grafting density is
decreased. Fig.4 shows the results of protein adsorption. It
1
is shown that both PVDF-g-T1S1 and PVDF-g-T2S1
membranes exhibit lowest protein absorption. XPS
analysis reveals that both modified membranes exhibit
zwitterionic-like structures. From XPS analysis, it can be
seen in Table 1 that the atomic ratio of N/S decreases as
the SA contents is increased. The N+(CH 3 ) 3 /SO 3 - moiety
ratio was close to unity for membranes prepared with a
monomer ratio of 1:1 (TMA:SA), which indicated that the
surface charge was neutral.
0.5
0.3
0.2
0.1
0.0
2
1S1
2S1
0S1
1S0
F
T1S
PVD DF-g-T VDF-g-T VDF-g-T VDF-g- DF-g-T
P
P
P
PV
PV
Fig.3. Effect of monomer ratio on grafting density
Relative Percentage (%)
150
Blood attachment persentage (%)
1000
Leukocyte
Erythrocyte
Platelets
750
500
250
0
BSA
Lysozyme
2
0
1
1
1
DF
T1S
T1S
T2S
T1S
T0S
PV
-g-g-g-g-gF
F
F
F
F
D
D
D
D
D
PV
PV
PV
PV
PV
Fig. 5. Effect of surface modification on the adhesion
of erythrocytes, leukocytes and thrombocytes.
120
90
DI water
60
BSA
DI water
BSA
DI water BSA
1200
0
1
2
2S1
0S1
1S0
F
T1S
T1S
PVD DF-g-T VDF-g-T VDF-g- VDF-g- DF-g-T
P
P
P
PV
PV
Fig. 4. Relative BSA and Lysozyme adsorption of
modified PVDF membranes.
DI water
PVDF
PVDF-g-T2S1
PVDF-g-T1S1
30
900
Flux (Kg/m2hr)
Grafting density (mg/cm2)
Treatment time = 60 s
0.4
PVDF-g-T1S1 membrane exhibit lowest adsorption of
Leukocytes, red blood cells and platelets.
Finally, the resistance of membranes to biofouling by
BSA proteins during filtration was tested. We observed
that the water permeability of pristine PVDF membranes
gradually decreased (Figure 6), while the flux recovery
ratio (FFR) was around 60%, which indicated that sites
were gradually fouled by BSA. As for grafted samples,
we suspected that a lack of surface uniformity was
responsible for the low flux recovery after the first cycle.
However, anti-biofouling efficiency of TMA and SA (2:1
or 1:1) is clearly seen during cycles 2 and 3, as very high
FRRs are obtained (91%-95%).
600
300
Table 1. XPS analysis of modified membrane.
N/S atomic
ratio
N+(CH 3 ) 3 /SO 3 - ratio
PVDF-g-T2S1
1.50
1.29
PVDF-g-T1S1
1.09
1.01
PVDF-g-T1S2
0.76
0.87
Sample ID
0
100
200
300
400
500
600
Time (min)
Resistance to biofouling is a requirement not only for
membranes applied in water treatment related
applications, but also for those applied in bloodcontacting devices. Fig. 5 shows the effect of surface
modification on the adhesion of erythrocytes, leukocytes
and thrombocytes. The positive-charged PVDF-g-T1S0
and PVDF-g-T2S1 membranes favour the adsorption of
blood cells and platelets, while the pseudo-zwitterionic
2
0
Fig. 6. Resistance of membranes to biofouling by BSA
protein during filtration.
4. Conclusion
Pseudo-zwitterionic TMA/SA copolymer was rapidly
grafted onto PVDF membrane by atmospheric-pressure
plasma. The modified membranes effectively resisted
protein adsorption, exhibited blood compatibility, and
showed a low biofouling during cyclic filtration.
5. References
[1] Y. Chang, W. J. Chang, Y. J. Shih, T. C. Wei, G. H.
Hsiue, ACS Appl. Mater. Interfaces 3, 1228 (2011).
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