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. 2022 Mar 17;15(6):2209.
doi: 10.3390/ma15062209.

Planar or Biaxial Stretching of Poly(ethylene terephthalate) Fiber Webs Prepared by Laser-Electrospinning

Tomoki Tokuda  1 , Ryo Tsuruda  1 , Takuya Hara  1 , Zongzi Hou  1 , Haruki Kobayashi  1 , Katsufumi Tanaka  1 , Wataru Takarada  2 , Takeshi Kikutani  3   4 , Juan P Hinestroza  5 , Joselito M Razal  6 , Midori Takasaki  1   4
Affiliations

Planar or Biaxial Stretching of Poly(ethylene terephthalate) Fiber Webs Prepared by Laser-Electrospinning

Tomoki Tokuda et al. Materials (Basel). .

Abstract

In this work, laser-heated electrospinning (LES) process using carbon dioxide laser was explored as an eco-friendly method for producing ultrafine fibers. To enhance the thinning of fibers and the formation of fiber structure, planar or equibiaxial stretching and subsequent annealing processes were applied to poly(ethylene terephthalate) (PET) fiber webs prepared by LES. The structure and properties of the obtained webs were investigated. Ultrafine fiber webs with an average diameter of approximately 1 μm and a coefficient of variation of 20-25% were obtained when the stretch ratios in the MD (machine direction) × TD (transverse direction) were 3 × 1 and 3 × 3 for the planar and equibiaxial stretching, respectively. In the wide-angle X-ray diffraction analysis of the web samples, preferential orientation of crystalline c-axis were confirmed along the MD for planar stretching and only along the web plane for equibiaxial stretching, which was in contrast to the stretching of film samples, where additional preferential orientation of benzene ring along the film plane proceeded. The results obtained suggest that PET fiber webs fabricated through LES and subsequent planar or biaxial stretching processes have potential for a wide variety of applications, such as packaging and battery separator materials.

Keywords: biaxial stretching; birefringence; crystallinity; melt electrospinning; planar stretching; poly(ethylene terephthalate); ultrafine fibers.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Schematic for the preparation of web sample by stretching. Photographs of the samples in the oven (b) before stretching, i.e., MD (machine direction) × TD (transverse direction) = 1 × 1, and after planar and simultaneous equibiaxial stretching with the stretch ratios of (c) MD × TD = 4 × 1, and (d) MD × TD = 4 × 4.
Figure 2
Figure 2
Diameter distribution of fibers in (a) the as-spun PET web and (b) the web after annealing (MD × TD = 1 × 1). The annealed webs after planar stretching at the stretch ratio of MD × TD = (c) 2 × 1, (d) 3 × 1, and (e) 4 × 1. The annealed webs after simultaneous equibiaxial stretching at the stretch ratio of MD × TD = (f) 2 × 2, (g) 3 × 3, and (h) 4 × 4. Average diameter and its coefficient of variation (CV) as well as the SEM image are shown for each web.
Figure 3
Figure 3
Orientation distribution of fibers in (a) the as-spun PET web and (b) the web after annealing (MD × TD = 1 × 1). The annealed webs after planar stretching at the stretch ratio of MD × TD = (c) 2 × 1, (d) 3 × 1, and (e) 4 × 1. The annealed webs after simultaneous equibiaxial stretching at the stretch ratio of MD × TD = (f) 2 × 2, (g) 3 × 3, and (h) 4 × 4.
Figure 4
Figure 4
Micrographs of the fibers observed under a polarizing microscope with cross-polarization: (a) raw fiber for LES, (b) as-spun web, (c) annealed web (MD × TD = 1 × 1), (d) annealed web after planar stretching (MD × TD = 4 × 1), and (e) annealed web after simultaneous equibiaxial stretching (MD × TD = 4 × 4). Directions of polarization for a polarizer and an analyzer are indicated in (a).
Figure 5
Figure 5
Correlation between fiber diameter and birefringence of a raw fiber and fibers in the web samples of various processing conditions.
Figure 6
Figure 6
DSC thermograms of (a) web and (b) film samples of various processing conditions.
Figure 7
Figure 7
Crystallinity analyzed from DSC thermograms for the web and film samples prepared by annealing after (a) planar stretching and (b) simultaneous equibiaxial stretching. Data for the raw fiber for LES, as-spun web, and as-received film are also included.
Figure 8
Figure 8
WAXD patterns of the (a) web and (b) film samples from various processing conditions obtained from the through, edge, and end directions. Machine direction (MD), transverse direction (TD), and normal direction (ND) are indicated in the figure.
Figure 9
Figure 9
WAXD intensity profiles against diffraction angle for the (a) web and (b) film samples annealed after stretching to various stretch ratios. The intensity profiles were obtained by averaging the intensity along the azimuthal angle of 0 to 180°. Data for the as-received film, raw fiber for LES, and as-spun web are also included.
Figure 10
Figure 10
WAXD intensity profiles against diffraction angle for the azimuthal angles (φ) of 0 and 90° for the (a) annealed web (stretch ratio of 1 × 1), (b) annealed web after planar stretching (stretch ratio of 4 × 1), (c) annealed web after simultaneous equibiaxial stretching (stretch ratio of 4 × 4).
Figure 11
Figure 11
WAXD intensity profiles against diffraction angle for the azimuthal angles (φ) of 0 and 90° for the (a) annealed film (stretch ratio of 1 × 1), (b) annealed film after planar stretching (stretch ratio of 4 × 1), and (c) annealed film after simultaneous equibiaxial stretching (stretch ratio of 4 × 4).
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