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. 2021 Mar 24;13(7):998.
doi: 10.3390/polym13070998.

Crystallinity and β Phase Fraction of PVDF in Biaxially Stretched PVDF/PMMA Films

Ye Zhou  1   2   3 , Wenting Liu  1   2   3 , Bin Tan  4 , Cheng Zhu  1   2   3 , Yaru Ni  1   2   3 , Liang Fang  1   2   3 , Chunhua Lu  1   2   3 , Zhongzi Xu  1   2   3
Affiliations

Crystallinity and β Phase Fraction of PVDF in Biaxially Stretched PVDF/PMMA Films

Ye Zhou et al. Polymers (Basel). .

Abstract

Polyvinylidene fluoride (PVDF) and poly(methyl methacrylate) (PMMA) blend films were prepared using biaxial stretching. The effects of PMMA content and stretching ratio on the crystallinity and β phase fraction of PVDF in blend films were investigated. The distributions of crystallinity and β phase fraction on variable locations were also studied. The results of FTIR and XRD showed that β phase appeared in PVDF/PMMA blends after extrusion and casting procedures. Although β phase fraction decreased after preheating, there was still an increasing trend during following biaxial stretching. More importantly, the increase in PMMA content improved β phase fraction, and the highest β phase fraction of 93% was achieved at PMMA content of 30 wt% and stretching ratio of 2×2. Besides, the reduction in PMMA content and the increase in stretching ratio improved the crystallinity of PVDF. The mechanical properties of the stretched films were significantly improved by increasing the stretching ratio as well. The uniform stress distribution on different regions of biaxial stretching films contributed to the uniform distribution of β phase fraction and crystallinity of PVDF with the aid of simulation. This work confirmed that biaxial stretching can be a candidate method to prepare PVDF/PMMA blend films with uniform distributions of comparable β phase and crystallinity of PVDF.

Keywords: PMMA; PVDF; biaxial stretching; crystallinity; thermo-mechanical fields; β phase.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Schematic diagram of extrusion, casting, preheating and biaxial stretching processing. (b) Photo of the biaxially stretching device. (c) Schematic diagram of the film during stretching.
Figure 2
Figure 2
DSC (a) heating and (b) cooling thermograms of PVDF, PVDF/PMMA blend VM and PMMA.
Figure 3
Figure 3
FTIR spectra of (a) the thermal-history free VM; (b) VM casting sheets; (c) VM casting Scheme 140 °C; and their (d) β phase fractions. (e,f) Schemes of chain orientations and evolution of α-β phases in casting sheets during extrusion, casting and preheating procedures.
Figure 4
Figure 4
(a–e) XRD patterns of VM casting films before and after preheating; (f) Crystallinities of VM casting films before and after preheating.
Figure 5
Figure 5
(a–c) FTIR spectra and (d–f) XRD patterns for the location of p1 in stretching VM films with ratios of 2 × 2, 2.5 × 2.5 and 3 × 3; (g–i) Schemes of crystal orientation in the film; (j) β phase fractions and (k) crystallinity versus PMMA content and stretching ratio.
Figure 6
Figure 6
The stress-strain curves of biaxial stretching PVDF/PMMA blend films with varied compositions, (a) VM15, (b) VM20, (c) VM25 and (d) VM30.
Figure 7
Figure 7
β phase fractions versus PMMA content and stretching ratio for the directions of (a) c, (b) p1, (c) p2, (d) d1 and (e) d2. And crystallinities versus PMMA content and stretching ratio for the locations of (f) c, (g) p1, (h) p2, (i) d1 and (j) d2.
Figure 8
Figure 8
(a) The stress-strain curves of input biaxial stretching date and the estimated biaxial stretching date. (b,c) COMSOL simulation results for the stretching size of (b) 12 × 12 cm2, (c) 15 × 15 cm2 and (d) 18 × 18 cm2.
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