Elsevier

Polymer

Volume 41, Issue 16, July 2000, Pages 6061-6066
Polymer

Application of a cycle zone-drawing/zone-annealing method to poly(ethylene terephthalate) fibers

https://doi.org/10.1016/S0032-3861(99)00851-4Get rights and content

Abstract

A cycle zone-drawing/zone-annealing method was applied to poly(ethylene terephthalate) fibers in order to improve their mechanical properties. An apparatus used for this treatment was assembled in our laboratory. The cycle zone-drawing (cyZD) treatment was carried out in three steps. The first cyZD treatment was carried out at a drawing temperature of 90°C under an applied tension of 8.7 MPa, the second at 90°C under 209 MPa, and third at 130°C under 366 MPa. The number of cycles in each cyZD was 5. Subsequently, the cycle zone-annealing treatment was applied to the cycle zone-drawn fiber and carried out at an annealing temperature of 210°C under 281 MPa at the cycle number of 50. The fiber obtained finally had a birefringence of 0.255 and a degree of crystallinity of 55%. This fiber exhibited a tensile modulus of 15.1 GPa, tensile strength of 1.2 GPa, and a storage modulus of 24.3 GPa at 25°C.

Introduction

Numerous studies have so far been carried out in the development of high-modulus and high-strength PET fibers. Fakirov et al. [1] used a two-stage cold drawing and reported a tensile modulus of 18.6 GPa and a tensile strength of 0.6 GPa. Ito et al. [2] reported that high molecular weight PET fibers, treated by using a multistep draw technique, showed a tensile modulus and strength of 39 and 2.3 GPa, respectively. We have also proposed many techniques producing high-performance fibers [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13]. A zone-drawing/zone-annealing method is one of such treatments leading to high-modulus and high-strength fibers. The treatment was applied to PET [14] and nylon 6 [15] fibers, being revealed to be effective improvement of their mechanical properties. Further, one expected that the high performance fiber would be produced by repeating the zone-drawing and zone-annealing. These treatments were named a cycle zone-drawing (cyZD) and a cycle zone-annealing (cyZA), respectively. An apparatus used for the cyZD and cyZA was assembled in our laboratory.

It is the purpose of the present paper to improve the mechanical properties of the fiber by the cyZD and cyZA treatments. The changes in the mechanical properties and microstructure were investigated using tensile testing, dynamic viscoelasticity, thermal mechanical analysis, X-ray diffraction, density, and birefringence measurements. Further, the results of this study are compared to these of our earlier study [14] on the mechanical properties and microstructure of the ZD/ZA PET fibers.

Section snippets

Material

The original material used in the present study was the as-spun PET fibers supplied by Toray Ltd. The original fiber had a diameter of about 0.25 mm and birefringence of 1.1×10−3. The original fiber was found to be amorphous and isotropic because only an amorphous halo was observed in the wide-angle X-ray diffraction photograph as shown in Fig. 1.

Apparatus for cycle zone-drawing and cycle zone-annealing

A schematic diagram of the apparatus used for the cyZD and cyZA treatments is given in Fig. 2. The apparatus consists of a temperature-controlled

Optimum conditions for the cyZD and cyZA treatments

The as-spun PET fiber was drawn in three steps by the cyZD treatment, and the cycle zone-drawn fiber (cyZD fiber) was subsequently annealed under tension by the cyZA treatment. The annealed fibers were designated as cyZA fibers. The purpose of the cyZD treatment is to (as much as possible) orient amorphous chains in the drawing direction without thermal crystallization. To achieve the objective in the drawing, the cyZD treatment was carried out at the temperature range between the glass

Conclusions

The cyZD and cyZA methods have been applied to poly(ethylene terephthalate) fibers to improve their mechanical properties. The degree of crystallinity increased to 33% by the cyZD treatments, increasing up to 55% by the subsequent cyZA treatment. The orientation factor of crystallites increased from 0 to 0.981 by only the first cyZD-1 treatment. On the contrary, the amorphous orientation factor increased with processing, and the cyZD-3 fiber had 0.802. Thus, the cyZD-3 fiber shows a higher

Acknowledgements

We acknowledge the financial support of the Grant-in-Aid for Scientific Research of the Ministry of Education, Science, and Culture, Japan.

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