Preparation and Properties of Poly(tetrafluoroethylene-co-hexafluoropropylene) Hollow Fiber Membranes†

doi:10.7503/cjcu20170053

Abstract

Abstract:

Poly(tetrafluoroethylene-co-hexafluoropropylene)(FEP) hollow fiber membranes(HFMs) were prepared by melt spinning method with FEP as polymer matrix, water solubility composite powder as pore-forming agent and dioctyl phthalate(DOP) as diluent. The effects of different concentrations of acid and alkali on the structure and properties of FEP HFMs were studied. The results show that the prepared FEP HFMs have a microporous structure with stretched pores, interface microporous and dissolved microporous, and the sponge-like microporous structure is evenly distributed on the cross-section. After 60 d immersed in 25% NaOH and H₂SO₄ solution, the chemical structure of the membranes has been unaffected, while the average pore size becomes larger and the pore size distribution narrows. The retention rates of break strength reach 86.8% and 80.8%, respectively. The acid and alkali resistance study indicates that the FEP HFMs have excellent chemical and thermal stability compared to commercial PVDF HFMs.

Key words: Poly(tetrafluoroethylene-co-hexafluoropropylene) hollow fiber membrane, Melt spinning, Chemical stability, High pure water flux

CLC Number:

O632.51

TrendMD:

YOU Yanwei, XIAO Changfa, WANG Chun, HUANG Qinglin, CHEN Mingxing, HUANG Yan. Preparation and Properties of Poly(tetrafluoroethylene-co-hexafluoropropylene) Hollow Fiber Membranes^†[J]. Chem. J. Chinese Universities, 2017, 38(9): 1678.

Figures/Tables 19

Fig.1 Schematic diagram of melt spinning process

Fig.2 Schematic diagram of pure water flux testing instrument

Fig.3 Morphologies of untreated FEP hollow fiber membranes(M0)(A) Cross section; (B) partial enlargement of cross section; (C) inner surface; (D) outer surface.

Fig.4 Schematic diagram of stretched pores formation process of FEP hollow fiber membranes

Fig.5 SEM images of FEP hollow fiber membranes immersed by 25% NaOH for 30 d(sample N3, A—C) and 60 d(sample N4, D—F)(A) and (D) Outer surface; (B) and (E) inner surface; (C) and (F) cross section.

Fig.6 SEM images of FEP hollow fiber membranes immersed in 10%(A—C) and 25%(D—F) H2SO4 for 30 d (A, D) Outer surface; (B, E) inner surface; (C, F) cross section.

Fig.7 SEM images of FEP hollow fiber membranes(sample H4) immersed in 25% H2SO4 for 60 d (A) Outer surface; (B) inner surface; (C) cross section.

Fig.8 EDX of FEP hollow fiber membranes (A) M0; (B) N4; (C) H4.

Fig.9 FTIR spectra of FEP hollow fiber membranes immersed in 25% NaOH(A) and 25% H2SO4(B) (A) a. M0; b. N2; c. N4. (B) a. M0; b. H2; c. H4.

Fig.10 DSC curves of M0(a), N4(b) and H4(c)

Fig.11 TG curves of M0(a), N4(b) and H4(c)

Fig.12 DMA curves of M0(a), N4(b) and H4(c)

Fig.13 Pore size distribution of M0, N2, N4, H2 and H4

Table 1 Minimum and average pore diameter of FEP hollow fiber membranes

Sample	Pore diameter_min/μm	Pore diameter_avg/μm
M0	0.3289	0.5468
N2	0.7896	1.0970
N4	0.9913	1.3591
H2	0.8533	1.1844
H4	1.1164	1.5201

Fig.14 Water contact angle of M0(A), N4(B) and H4(C)

Fig.15 Pure water flux of FEP hollow fiber membranes after NaOH(A)/H2SO4(B) treatment (A) a. N1; b. N2; c. N3; d. N4; e. M0. (B) a. H1; b. H2; c. H3; d. H4; e. M0.

Fig.16 Effect of acid and alkali solutions on rejection ratio of carbonic ink by FEP hollow fiber membranes

Table 2 Mechanical properties of hollow fiber membranes

Sample	Stress/MPa	Strain(%)	Stress retention ratio(%)	Sample	Stress/MPa	Strain(%)	Stress retention ratio(%)
M0	5.01	44.5	100	PVDF-0	4.98	84.3	100
N4	4.35	12.2	86.8	PVDF-H	3.11	30.9	62.4
H4	4.05	12.2	80.8	PVDF-N		1.9

Fig.17 External morphologies of M0(A), N4(B), H4(C), PVDF-O(D), PVDF-N(E) and PVDF-H(F)

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