Chem. J. Chinese Universities ›› 2017, Vol. 38 ›› Issue (1): 150.doi: 10.7503/cjcu20160580

• Polymer Chemistry • Previous Articles     Next Articles

Influence of Atmosphere and Force During Thermal Imidization on the Structure and Properties of BPDA-PDA Polyimide Fibers

YANG Wenke1,3, LIU Fangfang2,3, ZHANG Ensong1,3, QIU Xuepeng2,*(), JI Xiangling1,*()   

  1. 1. State Key Laboratory of Polymer Physics and Chemistry
    2. Polymer Composites Engineering Laboratory, Changchun Institute of Applied Chemistry,Chinese Academy of Sciences, Changchun 130022, China
    3. University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2016-08-15 Online:2017-01-10 Published:2016-12-12
  • Contact: QIU Xuepeng,JI Xiangling E-mail:xp_q@ciac.ac.cn;xlji@ciac.ac.cn
  • Supported by:
    † Supported by the National Basic Research Program of China(No.2014CB643603) and the National Natural Science Foundation of China(No.51173178).

Abstract:

The process of thermal imidization of polyamideacid(PAA) fibers affects the properties of the obtained polyimide(PI) fibersdirectly. Herein, the influence of atmosphere and force during thermal imidization on the structure and properties of PI fiber derived from 3,3',4,4'-biphenyltetra-carboxylic dianhydride(BPDA) and p-phenylenediamine(PDA) was studied. As PI fibers isothermally treated for 5 min, though there is no apparent difference on the morphology of their surface at different atmospheres, the highest tensile strength and initial modulus of fibers treated under nitrogen can reach about 1.25 and 65.0 GPa which are better than those treated in the air, indicating an effective protection of nitrogen atmosphere on the fiber. As longer treatment time of 40 min was applied, the protection of nitrogen atmosphere on the fiber surface was visible in the scanning electron microscopy(SEM) images. However, for the mechanical properties, the effect of atmosphere was only remarkably when fibers treated at 450 ℃. As PAA fibers treated at temperatures lower than 450 ℃, the long-time treatment became the main factor to influence the mechanical properties. And as PAA fibers treated higher than 450 ℃, the mechanical properties were lowered since the degradation of fibers in both atmospheres. As force is applied during the thermal imidization, the expansion of fibers during imidization can be enhanced. With increasing the applied force from 0.0025 N to 0.32 N, the length of the obtained PI fibers increases from 5.0% to 15.5% and the diameter decreases from 16.0 μm to about 12.8 μm. Moreover, it is found that all of the d-spacing of the (004) crystals faces, the crystal size along the fiber axis, the absolute value of coefficient of thermal expansion(CTE) and temperature of glass transition(Tg) of the fibers increase with the applied force. The tensile strength of fibers seems insensitive to the applied force and remains at about 0.90 GPa. The elongation decreases slightly from 2.50% to 2.30% and the initial modulus increases from 53.0 GPa to 65.0 GPa as the applied force increases.

Key words: Polyimide fiber, Polyamic acid, Thermal imidization, Atmosphere, Force

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