Acrylic Acid Grafting of Polyethylene Hollow Fiber Membranes in a Module Scale via Long-distance and Dynamic Low-temperature Plasma Flow†

doi:10.7503/cjcu20130841

Abstract

Abstract:

Long-distance and dynamic Ar low-temperature plasma flow pretreatment of polyethylene(PE) membrane in a module scale and subsequent acrylic acid(AA) grafting in aqueous solutions were developed to prepare hydrophilic PE hollow fiber membrane modules(PE-g-AA) successfully. This novel plasma chemical modification exhibited high efficiency, environment-friendly process and low surface etching. In the PE-g-AA membrane module, almost all contact angles along with fiber axial distance from the plasma inlet for outside membrane surfaces were close to 50°, far smaller than that of virgin membranes(about 120°). The improvement in surface hydrophilicity of PE-g-AA membrane was mainly due to the chemically grafted implantation of a large amount of —COOH polar groups onto outside membrane surfaces. Meanwhile, the uniform of chemistry and morphology for outside PE-g-AA membrane surfaces was improved greatly. Moreover, after 7 times water filtrations during 120 d storage, the steady water flux of PE-g-AA module was still about 1.5 times of that of virgin one, and its average contact angle recovered by only about 8°. The PE-g-AA module exhibited good hydrophilic stability. Also, the grafting reduced bovine serum albumin(BSA) fouling and increased pure water flux. After cleaning, the pure water flux of fouled PE-g-AA module during filtration of BSA aqueous solution can recover to about 81.79% of that of before fouling.

Key words: Plasma, Polyethylene hollow fiber membrane, Module, Grafting, Acrylic acid

CLC Number:

TrendMD:

LI Meisheng, ZHAO Zhiping, WANG Mingxing. Acrylic Acid Grafting of Polyethylene Hollow Fiber Membranes in a Module Scale via Long-distance and Dynamic Low-temperature Plasma Flow^†[J]. Chem. J. Chinese Universities, 2014, 35(4): 888.

Figures/Tables 10

Fig.1 Preparation process of the PE-g-AA membrane module via LDDLT plasma flow irradiation and subsequent graft polymerization and characterization measurement points (A) Plasma irradiation; (B) exposure to air; (C) grafting.

Fig.2 Dependence of the water contact angle for outside membrane surface on the distance from the plasma inlet(measured after 1 h of aging)

Fig.3 Dependence of the outside membrane surface morphology on the axial distance from the module inlet(A) Original; (B) plasma-treated; (C) PE-g-AA. Meansured position/cm: Label 1: 0—1; label 2: 10—11; label 3: 19—20.

Fig.4 FTIR spectra of plasma-treated PE(A) and PE-g-AA(B) membranes at different positions from the module inlet(outside membrane surface)a0, b0: Original PE; meansured position/cm: a1, b1. 0.5—1.0; a2, b2. 3.5—4.0; a3, b3. 7.5—8.0; a4, b4. 12.0—12.5; a5, b5. 17.0—17.5; a6, b6. 21.0—21.5.

Table 1 Elemental concentrations(%) of original PE, plasma-treated PE and PE-g-AA membranes at different positions from the module inlet

Outside membrane surface	Distance from the module inlet/cm	C	O	N	O/C	N/C
Original PE		94.70	5.73	0	0.060	0
	0—1	54.19	42.80	3.02	0.790	0.056
Plasma-treated PE	10—11	75.37	19.18	5.47	0.254	0.073
	19—20	75.80	18.72	5.48	0.247	0.072
	0—1	69.03	29.99	0.99	0.434	0.014
PE-g-AA	10—11	67.77	31.00	1.23	0.457	0.018
	19—20	69.20	29.65	1.15	0.428	0.016

Fig.5 XPS spectra of plasma-treated PE(A) and PE-g-AA(B) membranes at different positions from the module inlet(outside membrane surface) a0, b0: Original PE; meansured position/cm: a1, b1. 0—1; a2, b2. 10—11; a3, b3. 19—20.

Fig.6 BSA normalized flux of the original PE(a), plasma-treated PE(b) and PE-g-AA(c) membrane modules

Table 2 Flux, BSA rejection and FRR of the original PE, plasma-treated PE and PE-g-AA membrane modules

Membrane	$J W 0$ / (L·m^-2·h^-1)	J_WR/ (L·m^-2·h^-1)	FRR(%)	J₀/ (L·m^-2·h^-1)	J_F/ (L·m^-2·h^-1)	R₀(%)	R_F(%)
Original PE(Module D)	39.11	28.36	72.51	97.76	22.85	2.10	41.77
Plasma-treated PE(Module A)	56.26	44.46	79.03	94.83	24.78	8.33	50.95
PE-g-AA(Module C)	55.49	45.39	81.79	81.80	32.28	11.44	48.03

Table 2 Flux, BSA rejection and FRR of the original PE, plasma-treated PE and PE-g-AA membrane modules

Membrane	$J W 0$ / (L·m^-2·h^-1)	J_WR/ (L·m^-2·h^-1)	FRR(%)	J₀/ (L·m^-2·h^-1)	J_F/ (L·m^-2·h^-1)	R₀(%)	R_F(%)
Original PE(Module D)	39.11	28.36	72.51	97.76	22.85	2.10	41.77
Plasma-treated PE(Module A)	56.26	44.46	79.03	94.83	24.78	8.33	50.95
PE-g-AA(Module C)	55.49	45.39	81.79	81.80	32.28	11.44	48.03

Fig.7 Pure water fluxes as a function of filtration time after different aging times(A) Plasma-treated membrane module(Module E), ○ original PE, □ plasma-treated PE membrane module after different aging times; (B) PE-g-AA membrane module(Module B), □ original PE, ○ PE-g-AA membrane module after different aging times.

Fig.8 Dependence of the water contact angles for outside membrane surfaces on the distance from the plasma inlet, for different treatment processes□ Original PE; —?— plasma-treated after 7 times dynamic water filtrations for 90 d of aging(Module E); —☆— PE-g-AA after 7 times dynamic water filtrations for 120 d of aging(Module B).

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