Abstract
Interface issues urgently need to be addressed in high-performance fiber reinforced composites. In this study, different periods of O2 plasma treatment are proposed to modify twist-free polyimide (PI) filaments to improve hydrophilicity and mechanical and interfacial properties. Feeding O2 produces chemically active particles to modify the filament surface via chemical reactions and physical etching. According to the X-ray photoelectron spectroscopy (XPS) results, the PI filaments exhibit an 87.16% increase in O/C atomic ratio and a 135.71% increase in the C–O functional group after 180 s O2 plasma treatment. The atomic force microscope (AFM) results show that the root mean square roughness (Rq) of the treated PI filaments increases by 105.34%, from 38.41 to 78.87 nm. Owing to the increased surface oxygenic functional groups and roughness after O2 plasma treatment, the contact angle between treated PI filaments and water reduces drastically from the pristine state of 105.08° to 56.15°. The O2 plasma treated PI filaments also demonstrate better mechanical properties than the pristine PI filaments. Moreover, after O2 plasma treatment, the adhesion between PI filaments and poly(amic acid) (PAA) is enhanced, and the tensile strength of the polyimide/poly(amic acid) (PI/PAA) self-reinforced composites increases from 136 to 234 MPa, even causing the failure mode of the composite changes from adhesive failure to partly cohesive failure.
Highlights
Polyimide (PI) filaments as reinforcements for advanced composites have attracted considerable research attention for their favorable thermal stability, outstanding mechanical properties, excellent chemical and radiation resistance, and special dielectric properties [1,2,3,4,5]
To the best of our knowledge, the present reported plasma treatment of PI fiber mostly focused on the temperature-resistant properties of ordinary PI fiber or short PI fiber [23,24,25,26,27,28], and the mechanical properties of plasma treatment of high-performance PI filaments have never been reported
High-performance PI filaments were treated with O2 plasma with different time intervals for adhesion enhancement
Summary
Polyimide (PI) filaments as reinforcements for advanced composites have attracted considerable research attention for their favorable thermal stability, outstanding mechanical properties, excellent chemical and radiation resistance, and special dielectric properties [1,2,3,4,5]. The surface of the PI filaments is relatively smooth, chemically inert, and inherently hydrophobic, and leads to very poor interfacial adhesion between PI filaments and the matrix, which limits the PI filaments as the reinforcement agent in advanced composites [10,11]. Optimizing the surface properties of PI filaments to improve the PI filaments/matrix adhesion is urgently needed to obtain high-performance composites. Polymers 2018, 10, 695 gas-phase oxidation, heat treatment, polymerization treatment, cryogenic treatment, and plasma treatment [5,12,13,14,15,16,17,18,19] Among these methods (see Table S1), plasma treatment only works on the uppermost layer of the material without compromising the bulk properties. To the best of our knowledge, the present reported plasma treatment of PI fiber mostly focused on the temperature-resistant properties of ordinary PI fiber or short PI fiber [23,24,25,26,27,28], and the mechanical properties of plasma treatment of high-performance PI filaments have never been reported
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