Preparation of Hydrophilic Polypropylene/Polyvinyl Butyral Hollow Fiber Membranes by Melt-spinning-stretching†

doi:10.7503/cjcu20170784

Abstract

Abstract:

Polyvinyl butyral(PVB) as hydrophilic modification agent and polypropylene-g-maleic anhydride(PP-g-MAH) as a compatibilizer were blended with polypropylene(PP) in order to prepare hydrophilic PP/PVB hollow fiber membranes by melt-spinning and stretching(MS-S). The effect of PVB at different mass ratios on crystallization behavior and hydrophilicity of PP/PVB blends was investigated by differential scanning calorimeter(DSC) and water contact angle(WCA). The wide angle X-ray diffraction(WAXD) and small-angle X-ray scattering(SAXS) were used to analyze the effect of PVB at different mass ratios on the crystalline lamellar structure of PP/PVB hollow fiber after annealed. The pore dimensions and distribution of inner surface of PP/PVB hollow fiber membranes were measured using field emission scanning electron microscope(FESEM). In addition, the porosity and pure water flux of PP/PVB hollow fiber membranes were tested. The results showed that the hydrophilicity of PP /PVB blends was improved obviously because of WCA of PP/PVB blends reduced from 103° to 76° with the increase of PVB. At the same time, PVB accelerated the nucleation rate of PP because of PVB acted as heterogeneous nucleation effective. However, the maleic anhydride of PP-g-MAH was chemically bound to hydroxy of PVB, which also delayed the motion of molecular chain and leaded to imperfect crystal structure, especially excessive addition of PVB. The results confirmed WAXD and SAXS analysis. The crystallinity of PP/PVB2.5(2.5%PVB) hollow fiber was better than that of pure PP hollow fiber after annealed. The lamellar orientation, lamellar thickness, and structure of Shish-Kebab of PP/PVB2.5 hollow fiber were better than that of pure PP hollow fiber after annealed. The porosity of corresponding hollow fiber membrane was 66% and pure water flux was 320 L/(m²·h), which increased by 76.8% compared with that of the pure PP hollow fiber membrane.

Key words: Hydrophilic modification, Hollow fiber membrane, Lamellae, Water flux, Melt-spinning-stretching, Polypropylene/polyvinyl butyral(Ed.: W, Z)

CLC Number:

O631.1+1

TrendMD:

LUO Dajun, SHAO Huiju, JIN Jinbo, XIE Gaoyi, CUI Zhenyu, YU Jie, QIN Shuhao. Preparation of Hydrophilic Polypropylene/Polyvinyl Butyral Hollow Fiber Membranes by Melt-spinning-stretching^†[J]. Chem. J. Chinese Universities, 2018, 39(8): 1838.

Figures/Tables 13

Table 1 Compositions of the PP/PVB blends

Sample	w(PP)(%)	w(PP-g-MAH)(%)	w(PVB)(%)
Pure PP	100	0	0
PP/PVB2.5	97.5	2	2.5
PP/PVB5	95	2	5
PP/PVB7.5	92.5	2	7.5
PP/PVB10	90	2	10

Fig.1 Shapes of water drop on pure PP(A), PP/PVB2.5(B), PP/PVB5(C), PP/PVB7.5(D) and PP/PVB10(E)

Fig.2 DSC thermograms of pure PP(a), PP/PVB2.5(b), PP/PVB5(c), PP/PVB7.5(d) and PP/PVB10(e)(A) Cooling; (B) second heating.

Fig.3 DSC thermograms of hollow fibers(A) a. Pure PP; b. annealed PP; (B) a. annealed PP; b. annealed PP/PVB2.5; c. annealed PP/PVB5;d. annealed PP/PVB7.5; e. annealed PP/PVB10.

Fig.4 Crystallinity of pure PP and PP/PVB annealed hollow fibersa. Pure PP; b. PP/PVB2.5; c. PP/PVB5;d. PP/PVB7.5; e. PP/PVB10.

Fig.5 WAXD patterns of pure PP(A), PP/PVB2.5(B), PP/PVB5(C), PP/PVB7.5(D) and PP/PVB10(E)

Fig.6 Hollow fibers axes(A) and crystal planes with respect to fixed coordinates(A)

Fig.7 Azimuthal intensity curves(A) and diffraction spectra(B) of pure PP(a), PP/PVB2.5(b),PP/PVB5(c), PP/PVB7.5(d) and PP/PVB10(e)

Fig.8 SAXS patterns of pure PP(A), PP/PVB2.5(B), PP/PVB5(C), PP/PVB7.5(D) and PP/PVB10(E)

Fig.9 Curve of one-dimensional correlation function for pure PP(A) and PP/PVB blends(B) annealed hollow fibers(B) a. Pure PP; b. PP/PVB2.5; c. PP/PVB5; d. PP/PVB7.5; e. PP/PVB10.

Table 2 Microstructure characteristics of pure PP and PP/PVB annealed hollow fibers

Sample	L/nm	L_c/nm	L_tr/nm	L_a/nm
Pure PP	21.6	5.4	3.4	9.4
PP/PVB2.5	20.5	5.9	3.4	7.8
PP/PVB5	22.8	5.7	3.8	9.5
PP/PVB7.5	19.2	5.0	3.4	7.2
PP/PVB10	18.7	4.2	3.5	7.0

Fig.10 FESEM micrographs of microporous structure of membranes inner surface of pure PP(A),PP/PVB2.5(B), PP/PVB5(C), PP/PVB7.5(D) and PP/PVB10(E)

Table 3 Structure parameters and pure water flux of pure PP and PP/PVB hollow fiber membranes*

Sample	D_o/μm	D_i/μm	Thickness/μm	Porosity(%)	Flux/(L·m^-2·h^-1)
Pure PP	478	370	54	55	181
PP/PVB2.5	482	372	55	66	320
PP/PVB5	420	321	50	51	210
PP/PVB7.5	344	258	43	33	64
PP/PVB10	273	197	38	19	25

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