Atomic oxygen-resistant polyimide composite fibers based on wet spinning of polyamic acid-POSS ammonium salts

摘要

As a vital component of flexible cables in aerospace vehicles, outstanding atomic oxygen (AO) resistance is in demand for polyimide (PI) fibers. Herein, a series of PI composite fibers with different polyhedral oligomeric silsesquioxane (POSS) ammonium salt contents (0-20 wt%) is prepared by adding diethylamino-POSS into polyamic acid (PAA) solution followed by spinning via wet process. The average silicon contents of the fibers by ICP (i.e., 2.99 wt%) are similar to the surface silicon content (2.93 wt%) measured by XPS. The interaction between positive charges from diethylamino-POSS and negative charges from PAA chains gives rise to the even dispersion of diethylamino-POSS in PI composite fibers. All the composite fibers exhibit T-g at similar to 396 degrees C and T-5% at similar to 553 degrees C. Moreover, the fracture strength slightly increases from 0.57 GPa to 0.63 GPa with increasing POSS ammonium salt content from 0 wt% to 15 wt%. After AO erosion, SEM results exhibit lower roughness for composite fibers than pure PI fibers. As the ammonium salt content is increased from 0 wt% to 20 wt%, the lower mass loss with 0.15 mg cm(-2) is shown, and the retention rates of fracture strength and initial modulus are considerably improved from 59.65% to 89.09% and from 63.83% to 91.45%, respectively. Meanwhile, the decay rates of fracture strength of the composite fibers obviously decrease at the same AO fluence with increasing POSS ammonium salt content. XPS results of the fibers show that the contents of carbon atom decrease whereas the contents of silicon and oxygen atoms increase obviously after AO erosion. This result indicates that silicate passivation layers form on the fiber surfaces, and these layers prevent the fibers from further AO attack. (C) 2019 Elsevier Ltd. All rights reserved.