热亚胺化过程中气氛和拉力对BPDA-PDA聚酰亚胺纤维结构与性能的影响

研究了3,3',4,4'-联苯四酸二酐-对苯二胺(BPDA-PDA)型聚酰胺酸(PAA)纤维热亚胺化过程中气氛和拉力对聚酰亚胺(PI)纤维结构和性能的影响. 热处理过程中, 恒温处理5 min时, 虽然不同气氛下纤维的表面形貌并无明显差异, 但N₂气下所得纤维的力学性能明显优于空气下的样品, N₂气保护作用下, 最高断裂强度和初始模量分别达到1.25和65.0 GPa. 恒温处理40 min时, N₂气对纤维表面形貌有明显的保护作用. 但对于力学性能, 气氛的影响仅在450 ℃时表现得非常明显. 低于450 ℃时, 长时间的热处理成为影响纤维力学性能的主要因素, 气氛的影响变得不明显. 高于450 ℃时, 在N₂气和空气中的纤维皆发生明显的降解, 从而严重影响其力学性能. 热亚胺化过程中施加的拉力会促进纤维热酰亚胺化过程中的膨胀. 随着拉力的增加PI纤维长度增加, 同时直径减小. PI纤维轴上(004)晶面的间距、 晶粒尺寸、 线性热膨胀系数(为负值)的绝对值及玻璃化转变温度都随热处理时拉力的增加而增大. 纤维的断裂强度随拉力的变化基本保持在0.90 GPa左右, 断裂伸长率随着拉力增加稍有下降, 纤维的初始模量随拉力的增大而增加.

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

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 dian-hydride(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 imidiza-tion 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. 0μm to about 12. 8μm. Moreo-ver, 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.