This study introduces an ion-exchange enhanced adsorption method to create a titanium dioxide (TiO2)/polytetrafluoroethylene (PTFE) composite shell on polyimide (PI) fibers, improving their friction and wear performance. PTFE’s low coefficient of friction reduces fiber friction when applied to PI fiber surface. Introducing TiO2 improves the uniformity of the PTFE coating, further lowering the friction coefficient. The maximum reduction in the coefficient of friction of the PI/TiO2/PTFE composite fiber was 46%. During wear, PTFE forms a lubricating transfer film on the fiber wear interface, increasing wear resistance. TiO2 particles within the transfer film as a high-hardness filler, reinforcing the film and further improving fiber wear properties. The PI/TiO2/PTFE composite fiber achieved 1782 cycles to failure, approximately 300 times greater than the original fiber. Importantly, the composite fiber’s mechanical properties, surface energy, and interfacial bonding strength remain comparable to those of the original fiber. This approach offers a highly efficient method for enhancing PI fiber’s friction and wear properties, expanding its potential applications.

Lightweight and high-strength structural materials have long been a central objective in materials science. Due to the exceptional specific strength and low density, high-performance organic fibers and their composites have emerged as critical materials, attracting significant interest in both scientific research and advanced engineering applications. This study focuses on enhancing the compressive performance and load-bearing capacity of organic fibers, which are limited by microstructural defects and weak intermolecular interactions. Polyimide (PI) fibers were selected as the subject of this study. Acrylic acid and acrylo POSS were introduced into the internal pores of the fibers by swelling and penetration, and formed a cross-linked network within the fibers. Comprehensive evaluations of the mechanical properties, interfacial characteristics, and viscoelastic behavior of the modified fibers were performed, aiming to elucidate the underlying mechanism responsible for the enhanced compressive performance. The results demonstrate that the synergistic interaction between acrylic acid and acrylo-POSS effectively enhances intermolecular interactions and repairs microstructural imperfections. The compressive strength of monofilament increased from 356 MPa to 527 MPa, marking an enhancement of approximately 50%, while the modulus increased from 12.9 GPa to 16.1 GPa, corresponding to a 25% rise. Additionally, the compressive strength of the composite material increased from 261 MPa to 322 MPa, reflecting a 21.8% improvement. The fiber/resin interfacial shear strength also increased from 40 MPa to 50 MPa, demonstrating a 25.6% enhancement. This study introduces a promising post-treatment strategy for organic fibers, offering potential applications in advanced structural materials.

The focus of this work is a detailed comparative study of the changes induced by ultraviolet (UV) irradiation in polyimide (PI) films with different chemical structures. Five synthesized aromatic PI films were subjected to UV irradiation. The properties and structural evolution resulting from this irradiation were comprehensively evaluated using a combination of experiments and simulations. A mechanism for the UV irradiation-induced molecular chain breakage on the surface of PI films was proposed. After 1600 h of UV irradiation, the mechanical properties, heat resistance, and other macroscopic properties of the PI films were maintained at >70 % of their original values, and the surface of the PI films showed damages such as holes and cracks after UV irradiation. The mass loss and thickness loss of PI films caused by UV irradiation exhibited a strong correlation, while the density remained basically unchanged. In addition, an increase in the surface hydrophilicity of the PI films was observed. There was a breakdown of surface -C-C-, -C-N-, and -C-H bonds, accompanied by an increase in the content of -C-O- and -C=O bonds. Based on experimental surface characterization, it was proposed that UV irradiation of PI films primarily occurs at the surface. Molecular simulations were performed to calculate the energy gap to undergo energy level jumps and the energy of the chemical bonds to break for the PI films, and it was hypothesized that the UV irradiation resistance of the PI films is related to the optical transmittance and the ease of charge-transfer complex (CTC) formation.

With the development of high-performance organic fiber reinforced composites, challenges related to fiber microstructural defects and surface inertness have attracted increasing attention. To address these issues, this study proposes effective and commercially viable strategies for restoring sub-microstructures and activating fiber surfaces. Through the synergistic effect of acetone and epoxy, the epoxy not only adsorbed onto and activated the fiber surface but also deeply penetrated into the fibers, thereby restoring the fibril-void structure. The multifunctional epoxy significantly improved the structural and interfacial strength, leading to significant improvements in the tensile and compressive strength of the monofilament, with increases of 15 % and 59 %, respectively. Upon preparation into a composite, the interfacial shear and compressive strength were enhanced by 75 % and 53 %, respectively. Furthermore, molecular dynamics simulations revealed that the interfacial enhancement mechanism is closely associated with the increased interfacial energy and thickness, as well as the enhanced reactivity of the epoxy.

To address the issues of the surface inertness and poor compression resistance of polyimide (PI) fibers, a series of PI/SiO2 composite fibers were prepared by using a vapor deposition method to deposit an SiO2 shell on the surface. The laws governing the evolution of the chemical structure and thickness of the SiO2 shell over the vapor deposition time were investigated, and the effects of the properties of the shell layer on the surface contact angle, surface energy, interfacial shear strength (IFSS), mechanical properties of the monofilament, and compressive performance of the composites were explored. The results indicated that a uniform SiO2 shell can be constructed on the PI fiber surface by the vapor deposition method. In comparison to the Origin, the surface energy and IFSS of the PI/SiO2 composite fibers exhibited remarkable increases of 51% and 39%, respectively. The compressive strength of both monofilament and multifilament composites showed significant increases, rising from 350.8 to 613.5 MPa and from 268.5 to 345.8 MPa, respectively. The study presents a novel technical approach for the surface inorganic modification of high-performance fibers and offers a fresh solution for improving the interface and compressive properties of organic fibers and their composites.Highlights A dense SiO2 shell-coated polyimide fiber was prepared by vapor deposition. Shell thickness was modulated by controlling the deposition time. The surface energy of the fiber was increased by approximately 51%. The compressive strength of polyimide fiber was enhanced by nearly 75%. The SiO2 shell improved the interfacial properties of the fibers.

The impact of chemical structure and environment on the thermal stability of polyimide (PI) was examined, and the degradation mechanism was determined using a combination of experiments and molecular simulations. Changes in mechanical properties and thermogravimetric analysis (TGA) were used to characterize the thermal stability of PI. Pyrolysis gas chromatography mass spectrometry (Py-GCMS) and thermogravimetric-infrared spectroscopy (TG-IR) were used to analyze the degradation products both qualitatively and quantitatively. Molecular simulation was employed to analyze the primary bond breakage and thermal degradation pathways of PI, as well as to investigate the effects of the chemical structure, atmosphere, and temperature on degradation properties. The findings indicated that p-benzene-structured 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)/p-phenylenediamine (PDA) has the best thermal stability, whereas weak bonds like C–O–C in 4,4′-oxydianiline (ODA) and C–N in the 2-(4-aminophenyl)-1H-benzimidazol-5-amine (BIA) imidazole group decrease thermal stability. The formation path of low molecular weight products (CO2, CO, HCN, and NH3) and the potential degradation mechanism of PI were proposed. The process of PI thermal degradation accelerated by oxygen and high temperature was observed at the atomic level. Taken together, this work offers the possibility of monitoring the structural evolution of PI degradation process in real-time.

In order to solve the problem of high-water absorption and low transparency of benzimidazole polyimide (PBII) films, this study introduced fluorine-containing groups into the benzimidazole polyimide molecule chains, and a series of benzimidazole polyimide films with different fluorine-containing ratios were prepared. In addition, a micro-branched crosslinking structure was established by adding triamino compounds to the system, and the effect of the micro-branched crosslinking structure on the film properties was investigated. The research showed that adding a certain amount of fluorine-containing groups could effectively improve the optical properties and decrease water absorption of polyimide films while having a small effect on the heat resistance and thermal dimensional stability. The incorporation of a small amount of triamino compounds effectively compensated for the adverse effects on the mechanical properties, heat resistance, and thermal dimensional stability caused by the addition of fluorine-containing groups and lowering the imidization temperature. In addition, the water absorption could be further reduced by establishing a cross-linked structure. In this study, a new design idea was provided to achieve the balance of heat resistance, thermal dimensional stability, water absorption, transparency, and mechanical properties of benzimidazole polyimide films.

The compressive performance of organic fiber has always been a key problem, limiting its development. In this paper, silicon oxide, alumina, and titanium oxide particles were separately deposited on the surface of high-strength and high-modulus polyimide (PI) fibers to form a structural supporting shell by using a magnetron sputtering method. The theoretical thickness was calculated by thermogravimetric analysis in good agreement with the actual thickness determined from scanning electron microscopy. The mechanics, surface, and interface properties of the measured fibers were analyzed mainly from the aspects of surface energy, interfacial shear strength (IFSS), and compression strength. The results showed that after magnetron sputtering, the inorganic shells were uniformly deposited on the surface of PI fiber, resulting in an increase in the content of inorganic elements as well as the roughness. As a result, the surface energy and IFSS of silica-coated fiber was increased by 174 and 85.6%, respectively, and compression strength was increased by 45.7%. This study provides a new approach for improving the interface property and compression strength of high-strength and high-modulus PI-fiber-reinforced composites.

A series of PI/ZrO2 composite fibers was prepared by the in-situ polar adsorption-hydrolysis method to improve compression properties. The influence of the ZrO2 shell on the surface, interface and compression properties of the PI fiber was evaluated through scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, microsphere debonding, monofilament tensile recoil, and multifilament composite compression. The results demonstrate a 50% increase in the compressive strength of monofilament and a 16% increase in composites. Additionally, effective modification of the surface properties of the fibers lead to a remarkable enhancement of 78% in interfacial shear strength (IFSS). Moreover, improvements were also observed in both tensile strength and thermal stability of the monofilament. It provided a new technical way for the improvement of the interface property and compressive strength of organic fiber reinforced composites.

采用S35高强型聚酰亚胺(PI)纤维作为增强体,热塑性树脂作为基体,采用热压工艺制备了织物结构和正交单向无纬(UD)结构复合材料靶板,通过弹道极限速度测试和背部变形测试,研究了增强体结构和界面结合强度对PI纤维增强热塑性树脂基复合材料防弹性能的影响.结果表明:高强型聚酰亚胺纤维表现出了优异的防弹性能;UD结构靶板更适用于防铅芯弹;织物结构靶板更适用于防破片;当界面剥离强度由5.45N/cm提高到26.44 N/cm时,剥离后界面处的纤维表面形貌的破坏程度逐渐增加.当侵彻体为5.6g铅芯弹时,随着界面剥离强度的提高,复合材料靶板的防弹性能呈现出先提高后降低的趋势;并且靶板的背部变形逐渐减小,进一步证明了界面结合强度对复合材料靶板防弹性能的影响.

针对超高分子量聚乙烯(UHMWPE)纤维增强防弹复合材料背部凸起(BFS)较高的不足,本研究充分利用聚酰亚胺(PI)纤维耐高温、高模量的优势,制备了一系列PI和UHMWPE纤维混杂复合材料靶板,研究了混杂靶板的铺层结构和混杂比例对比吸收能(SEA)值和背部凸起(BFS)值的影响,分析了混杂靶板防护作用机制.结果显示:PI纤维的使用可以在不影响SEA值的情况下有效限制BFS值,其中两极铺层结构(H3、UHMWPE/PI)和夹芯铺层结构(H4、PI/UHMWPE/PI)表现出混杂正效应,两种结构的SEA值和BFS值分别可达193.2 J·m2/kg,17.40 mm和208.9 J·m2/kg,17.77 mm,表现出优异的防弹性能.

高强高模聚酰亚胺(PI)纤维是近年来出现的一种新型高性能有机纤维,具有优异的力学性能、耐高低温性能、低介电、高绝缘、高阻燃、耐辐照等综合性能,在航天、航空、安全防护、核工业等领域具有广阔的应用前景.本工作着重针对高强高模PI纤维在航天领域中的应用需求,特别是在空间环境中的应用特点,分析了其在极端温度、交变温度、粒子辐照、高真空以及长期负载等环境下的性能表现,初步考核了其空间环境适应性,以期为其相关应用提供设计依据.研究结果显示,高强高模PI纤维表现出优异的力学性能、耐高低温、耐粒子辐照、抗蠕变等综合性能,在350℃条件下其拉伸强度和拉伸模量仍分别可达到1.55 GPa和27.74 GPa,经1.0×108 rad(Si)剂量粒子辐照后,拉伸性能保持率高于98％.此外,本工作还结合PI纤维的综合性能表现对其在航天领域的应用前景进行了展望.

Bilayer polyimide film with superparamagnetic response and conductive surface has been exploited as an important candidate for electromagnetic interference shielding material. Poly-imide matrix was derived from 4,4’-oxydianiline and 3,3’,4,4’-benzophenonetetracarboxylic dianhydride. Iron (III) 2,4-pentanedionate (Fe(acac)3) and (1,1,1-trifluoro-2,4-pentadionato) silver(I) (AgTFA) were chosen as magnetic nanoparticles precursor and silver source, respectively. At magnetic polyimide layer, in situ method allowed the Fe(acac) 3 to decompose to γ-Fe2O3, exhibiting typical superparamagnetic response. The conductive surface-silvered poly-imide layer was prepared via in situ single-stage self-metallization technique by thermal curing of the AgTFA-contained poly(amic acid). The reduction of silver(I) and further aggregation of silver atoms gave the conductive polyimide surface. The surface square resistance for the bilayer film of 0.1 Ω/square could be obtained. The structure and the properties of final bilayer f...

Surface silvered polyimide (PI)/Fe2O3 composite films with both superparamagnetic and surface electrically conductive properties have been fabricated by an in situ technique. Iron (III) 2,4-pentanedionate was incorporated into a PI precursor poly(amic acid) solution and thermally decomposed to form iron oxide nanoparticles in the process of thermal imidization, preparing PI/Fe2O3 nanocomposite films. The establishment of a silver layer on the PI/Fe2O3 film surface involved the steps of chemical etching by the alkaline aqueous solution, ion exchange with silver ions and chemical reduction by glucose. The formed Fe2O3 particles of the nano scale endow the film with typical superparamagnetic response. By employing the etching time of only 10min and a reduction time of no more than 15min, the well-established silver layers have formed on the upside surface. The corresponding reflectivity and resistivity reached to the value of 76.15% and 0.7Ω/square respectively.

Hybrid layers consisting of copper nanoparticles and polyimide have been successfully fabricated using copper nitrate as the copper precursor and pyromellitic dianhydride/oxydianiline-(PMDA/ODA-) based polyimide films as the substrate. The fabrication method relies on the potassium hydroxide-induced chemical modification of the polyimide surface to introduce carboxylic acid groups, the incorporation of copper ions through subsequent ion exchange reaction, and followed by the polyol in situ reduction of copper ions contained polyimide layers in ethylene glycol solution at 197 degrees C. The amount of copper ions in the modified layer strongly depended on the ion exchange time. The copper nanoparticles size changed from 3 nm to 27 nm when the reduction time increased from 5 min to 30 min. These experiments provided an efficient route for copper metallization of polyimide substrate. The detailed reaction progress and resulted films were characterized by Attenuated total reflection-Fourier transform infrared, X-ray photoelectron spectroscopy, inductively coupled plasma atomic emission spectrometer, X-ray diffraction, transmission and scanning electron microscope.

A simple method was developed to directly deposit silver nanoparticles on the surface of silica spheres. The photochemical reduction was carried out by ultraviolet irradiation in air atmosphere at room temperature. The [Ag(NH3)2]+was reduced to silver atoms upon ultraviolet irradiation. Silver atoms subsequently deposited on the surface of silica spheres and agglomerated into silver nanoparticles. Silica spheres with silver nanoparticles of different size and density can be simply controlled by adjusting the UV-light irradiation time. The silver nanoparticles deposited on silica spheres were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy.

Silver quantum dots (QDs) embedded silica/PAAc hybrid nanoparticles were prepared by copolymerization of acrylic acid (AAc) onto γ-Methacryloxypropyltrimethoxysilane (MPS) modified silica nanoparticles followed by reduction of the immobilized Ag+ ions to metallic Ag. The prepared hybrid nanoparticles were characterized using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The hybrid nanoparticles dispersed well in aqueous media and showed effective bactericidal activities. The results suggest that the hybrid nanoparticles have potential application as a water-soluble agent in many fields.

A new route to porous polyimide (PI) films with pore sizes in the nanometer regime was developed. A polyamic acid (PAA)/polyurethane (PU) blend with PU as the disperse phase was first prepared via in situ polymerization of pyromellitic dianhydride and 4,4-oxydianiline in PU solutions. Porous PI films were obtained from PAA/PU films by thermolysis of PU at 360°C and imidization of PAA at 300°C, respectively. Fourier transform infrared spectroscopy and thermal gravimetric analysis were used to detect the imidization and thermolysis processes of PAA/PU blends under thermal treatment. The microporous structure of the PI films was observed by transmission electron microscopy. It was found that the size and content of pores increased with an increase in the PU mass fraction in the PAA/PU blend up to 20%. Because of the existence of nanopores, the dielectric constant of PI films decreased by a wide margin and was less than 2.0 at a PU mass fraction of 20%. It implies that this is an effective means to reduce the dielectric constant of PI, but it also causes the decrease of tensile strength and the rise of water absorption.