Synthesis of Oil/Water Separation Membranes via Grafting Acrylic Acid onto Poly(vinylidene fluoride) Modified by Tetraethyl Ammonium Hydroxide†

doi:10.7503/cjcu20160224

Abstract

Abstract:

Poly(vinylidene fluoride)-graft-poly(acrylic acid)(PVDF-g-PAA) membranes were prepared via phase bulk modification in tetraethyl ammonium hydroxide(TEAH) liquid, grafting acrylic acid(AA) onto PVDF by benzoyl peroxide(BPO) as a initiator. After that, the copolymer was casted into a flat membrane via immersion phase inversion. The chemical composition, morphology and the separation performance of the PVDF-g-PAA membrane were charaterized. Moreover, the effect of variable grafting conditions on grafting degree was investigated as well as the optimal surface contact angle for the grafting ration was obtained. It was proved that the PVDF was taken off HF to produce carbon double bonds and acrylic acid was grafted onto the modified PVDF backbones, forming a homogeneous pore distribution in interior and exterior of the membrane. The water contact angle of PVDF-g-PAA membranes decreased with increasing the grafting degree. The optimized hydrophilicity of the modified PVDF membrane was modified with 45%(mass fraction) of AA at 85 ℃ for 4 h, when this condition the grafting degree of membrane was 20.1%; the porosity and mean pore size was 65.3% and 78.0 nm, respectively; the contact angle decreased from 57.5° to 14.3° within 60 s. Water flux increased to 571.33 L/(m²·h), rejection ratio and flux recovery ratio up to 94.3% and 88.7%, respectively. The flux decline ratio was only 9.8%. The separation performance of the PVDF-g-PAA membrane was significant improvement compared to that of the pure PVDF membrane.

Key words: Oil/water separation membrane, Poly(vinylidene fluoride), Bulk modification, Tetraethyl ammonium hydroxide, Acrylic acid(Ed.: D, Z)

CLC Number:

O632.21

TrendMD:

YAN Kaibo,GUO Guibao,LIU Jinyan. Synthesis of Oil/Water Separation Membranes via Grafting Acrylic Acid onto Poly(vinylidene fluoride) Modified by Tetraethyl Ammonium Hydroxide^†[J]. Chem. J. Chinese Universities, 2016, 37(8): 1565.

Figures/Tables 13

Scheme 1 Synthesis of the PVDF-g-PAA

Fig.1 FTIR spectra of pure PVDF membrane(a), modified PVDF membrane(b) and PVDF-g-PAA membrane(GD=20.1%)(c)

Fig.2 Wide-scan XPS spectra of PVDF(A) and PVDF-g-PAA(GD=20.1%)(B) membranes

Table 1 Element relative atomic percentage as determined by XPS analysis

Sample	Elemental content(%)
Sample	C	F	O
PVDF	63.81	36.19	0
PVDF-g-PAA	64.78	26.10	9.12

Fig.3 SEM images of top surface(A1, B1) and cross-sectional morphology(A2, B2) of pure PVDF membrane(A1, A2) and PVDF-g-PAA(GD=20.1%)membrane(B1, B2)

Table 2 Porosity and pore size of pure PVDF membrane and PVDF-g-PAA(GD=20.1%) membrane

Membrane	ε(%)	r_m/nm
PVDF	58.2	42.5
PVDF-g-PAA	65.3	78.0

Fig.4 Relation between the mass concentration of AA and the GD of PVDF-g-PAA membranes

Fig.5 Relation between grafting temperature and the GD of PVDF-g-PAA membranes

Fig.6 Relation between grafting time and the GD of PVDF-g-PAA membranes

Fig.7 Effect of the GD on the contact angle of PVDF-g-PAA membranes

Fig.8 Images of 1 μL water droplets at various time on pure PVDF membrane(A) and PVDF-g-PAA(GD=20.1%) membrane(B)

Fig.9 Time-dependent flux of pure PVDF membrane(a) and PVDF-g-PAA(GD=20.1%)(b) membrane during water filtration, oil/water emulsion filtration, water filtration after being clean

Fig.10 Rejection ratio(R), flux recovery ratio(FRR) and flux decline ratio(D) of pure PVDF membrane and PVDF-g-PAA(GD=20.1%) membrane

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