Effect of Hot Stretching on the Structure of Polypropylene Microporous Membranes with in situ Small Angle X-Ray Scattering†

doi:10.7503/cjcu20170184

Abstract

Abstract:

With in situ small angle X-ray scattering and scanning electron microscopy measurements, effects of hot stretching temperatures and draw ratios on the lamellae and pore structure of the polypropylene microporous membrane were studied. The results show that the lamellar clusters are separated during the cold stretching and heat setting process, while the internal structures do not undergo separation during the hot stretching process. With the increase of the hot stretching ratio, the bridge length of microporous membrane after hot stretching process increases substantially. Also, it has better periodicity along the equatorial direction compared with the cold-stretching and heat-setting samples. The results of different stretching temperatures show that the length of the bridge increases with the increase of the stretching temperature. When the temperature is too high, the bridge will partially melt. This work can provide guidance for the structural control during preparation of polypropylene microporous membranes.

Key words: Polypropylene microporous membrane, In situ small angle X-ray scattering, Cold stretching-heat setting-hot stretching, Micropore, Lamellar cluster

CLC Number:

O631

TrendMD:

WANG Wei, XU Jiali, LIN Yuanfei, LI Xueyu, MENG Lingpu, LI Liangbin. Effect of Hot Stretching on the Structure of Polypropylene Microporous Membranes with in situ Small Angle X-Ray Scattering^†[J]. Chem. J. Chinese Universities, 2017, 38(11): 2128.

Figures/Tables 11

Fig.1 Pictures of the tensile apparatus for microporous membrane preparation(A) and polypropylene microporous membrane after stretching(B)

Fig.2 2D SAXS patterns of samples stretched to 30% at room temperature and then hot stretched with different strains(A1—A4), heat-set(B1—B4) and cooled down(C1—C4)(A1—C1) L0.3R1.0; (A2—C2) L0.3R1.5; (A3—C3) L0.3R2.0; (A4—C4) L0.3R2.5.

Fig.3 SEM images of L0.3 and other membranes with different hot stretching ratios(A) L0.3R1.0; (B) L0.3R1.5; (C) L0.3R2.0; (D) L0.3R2.5; (E) L0.3.

Fig.4 Average length of bridges(a), lamellar stack thickness(b), mean lamellar thickness(c) and long period(d)

Fig.5 Curves of one-dimensional electron density correlation functionInset: long period(L) and amorphous thickness(da).

Fig.6 SAXS integral curves along equatorial direction of L0.3 and microporous films made of different draw ratios at higher temperature

Fig.7 SAXS patterns of different stretching temperature during hot stretching(A1—A3), heat setting(B1—B3) and cooling down(C1—C3) (A1)—(C1) W127; (A2)—(C2) W135; (A3)—(C3) W153.

Table 1 Some parameters of different hot stretching temperatures

State	W₁₂₇		W₁₃₅		W₁₅₃
State	L/nm	d_c/nm	L/nm	d_c/nm	L/nm	d_c/nm
Heat stretching	22.9	12.7	22.9	12.7	23.7	13.4
Heat setting	23.7	13.3	24.1	13.7	23.3	12.6
Cool down	22.9	12.7	24.1	13.7	22.9	12.7

Fig.8 SEM images of microporous films made at different hot stretching temperatures(A) W127; (B) W135; (C) W153.

Fig.9 Bridge length and lamellar stack thickness

Fig.10 SAXS integral curves of equatorial direction of samples made at different hot stretching temperatures

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