High-performance aromatic polyimide fibres: 2. Thermal mechanical and dynamic properties
High-performance aromatic polyimide fibres: 2. Thermal mechanical and dynamic properties
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DOI：
10.1016/0032-3861(93)90392-n
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发表时间：
1993
期刊：
影响因子：
4.6
通讯作者：
Mark Eashoo;D. Shen;Zongquan Wu;Chul Joo Lee;F. Harris;Stephen Z. D. Cheng
中科院分区：
文献类型：
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作者：
Mark Eashoo;D. Shen;Zongquan Wu;Chul Joo Lee;F. Harris;Stephen Z. D. Cheng
采用干喷湿纺法，从凝胶态或各向同性溶液中纺出一系列高温、高模量芳香族聚酰亚胺纤维，然后进行高温拉伸。本文详细介绍了由3，3 ′，4，4 ′-联苯四甲酸二酐（BPDA）和2，2 ′-二（三氟甲基）-4，4 ′-联苯二胺（PFMB）合成的嵌段刚性棒聚酰亚胺的热性能和动态力学性能。拉伸可显著提高BPDA-PFMB纤维的力学性能，这是由于纤维的整体取向、晶体取向和结晶度显著增加。然而，这三个结构参数并没有显示出随拉伸比增加的平行变化。已经观察到，当在测量期间施加低应力时，拉伸后BPDA-PFMB纤维的线性热膨胀系数（CTE）在固态下通常显示负值。对于初生纤维，CTE在一定的施加应力区域内是恒定的，其与沿膜表面沿着面内取向的BPDA-PFMB膜的CTE处于相同的数量级。这可能表明，在该区域内，所施加的应力与纺丝和拉伸过程中冻结在纤维中的内应力处于相同水平。初生纤维的玻璃化转变温度（Tg）在低应力区呈线性下降，然后在高应力区趋于稳定。动态力学数据表明，在室温以上，初生纤维有两个弛豫过程：一个是对应于玻璃化转变的α弛豫，另一个是亚玻璃化转变的β弛豫。在拉伸倍数大于3倍的纤维中，α松弛被完全抑制。这揭示了一个刚性分数（高于Tg）的依赖性，这种松弛的纤维。另一方面，β驰豫取决于结晶度。初生纤维中β松弛的阿耳忒修斯活化能（约160 kJ mol−1）比拉伸纤维低约50 kJ mol− 1，表明纤维中分子运动的协同性随取向和结晶度而变化。
A family of high-temperature, high-modulus aromatic polyimide fibres has been dry-jet wet spun from either its gel state or isotropic solution, followed by high-temperature drawing. In this report, thermal and dynamic mechanical properties of one of the family members, a segmented rigid-rod polyimide synthesized from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB), are presented in detail. Mechanical properties of these BPDA-PFMB fibres can be improved remarkably by drawing due to drastic increases in overall orientation, crystal orientation and crystallinity. These three structural parameters, however, do not show parallel changes with increasing draw ratio. It has been observed that the linear coefficient of thermal expansion (CTE) of BPDA-PFMB fibres after drawing generally show negative values in the solid state when low stresses are applied during measurements. For as-spun fibres, the CTEs are constant over a certain applied stress region, which is on the same order of magnitude as CTEs of in-plane oriented BPDA-PFMB films along the film surface. This may be an indication that within this region the stress applied is at the same level as the internal stress frozen into the fibres during spinning and drawing. Glass transition temperatures (Tg) of as-spun fibres show a linear decrease at low applied stress region, then level off when the applied stress becomes high. Dynamic mechanical data indicate two relaxation processes in as-spun fibres above room temperature: an α relaxation corresponding to the glass transition and a β relaxation which is a subglass transition. In the fibres with a draw ratio of above three times, the α relaxation is totally suppressed. This reveals a rigid fraction (aboveTg) dependence of this relaxation in the fibres. The β relaxation is, on the other hand, crystallinity dependent. The Arrhenius activation energy (about 160 kJ mol−1) of the β relaxation in as-spun fibres is about 50 kJ mol−1lower than that of drawn fibres, indicating that the cooperativity of molecular motion in the fibre changes with orientation and crystallinity.