四乙基氢氧化铵改性聚偏氟乙烯接枝聚丙烯酸油水分离膜的制备

doi:10.7503/cjcu20160224

摘要/Abstract

摘要：

使用四乙基氢氧化铵(TEAH)液相本体改性聚偏氟乙烯(PVDF), 以过氧化苯甲酰(BPO)为引发剂, 将丙烯酸(AA)接枝到改性PVDF骨架上, 合成了聚偏氟乙烯接枝聚丙烯酸(PVDF-g-PAA)共聚物, 通过浸没沉淀法制备了PVDF-g-PAA亲水性油水分离膜. 通过傅里叶变换红外光谱(FTIR)、扫描电子显微镜(SEM)和过滤试验分析了膜的结构和分离性能. 研究了不同接枝条件对PVDF-g-PAA膜接枝率的影响. 同时, 通过膜接枝率与膜表面接触角的关系确定最佳接枝条件. 结果表明, TEAH使PVDF脱去HF产生碳碳双键且PAA接枝到改性的PVDF骨架上, 膜内外孔隙分布均匀; PVDF-g-PAA膜的接触角随着接枝率的提高而降低. 接枝单体AA含量为45%, 接枝温度为85 ℃, 接枝4 h制备的PVDF-g-PAA膜的接枝率为20.1%, 孔隙度为65.3%, 平均孔径为78.0 nm, 接触角为57.5°, 且在60 s内接触角降至14.3°; 纯水通量提高到571.33 L/(m²·h), 截留率和水通量恢复率分别达到94.3%和88.7%, 且通量衰减率仅为9.8%. 与纯PVDF膜相比, PVDF-g-PAA膜的分离性能显著提高.

关键词: 油水分离膜, 聚偏氟乙烯, 本体改性, 四乙基氢氧化铵, 丙烯酸

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)

中图分类号:

O632.21

TrendMD:

闫凯波, 郭贵宝, 刘金彦. 四乙基氢氧化铵改性聚偏氟乙烯接枝聚丙烯酸油水分离膜的制备. 高等学校化学学报, 2016, 37(8): 1565.

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^†. Chem. J. Chinese Universities, 2016, 37(8): 1565.

图/表 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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