Polyimide Fibers Research Articles

Porous Ti3C2Tx MXene nanosheets sandwiched between polyimide fiber mats for electromagnetic interference shielding

Porous Ti3C2Tx MXene nanosheets sandwiched between polyimide fiber mats for electromagnetic interference shielding

Lightweight, low dielectric and heat-resistant polyimide fiber bulkpaper developed via alkali activated strategies for advanced insulation

With the prosperity of aviation, aerospace, and military equipment, critical requirements asked for insulating materials, which not only seek outstanding insulation, and low dielectric but also put particular emphasis on lightweight and heat resistance features. Herein, to enhance polyimide (PI) fibers bulkpaper, surface modification strategies were proposed and researched. Specifically, the hydrolysis effects of NaOH/DMAc and NaOH/H2O systems on PI fibers and PI fibers bulkpaper were investigated. The results indicated that the NaOH/DMAc system possessed more effective activation, which was proved by the contents of O elements and CO groups. Besides, the PI fibers bulkpaper derived from alkali-activated PI chopped fiber was developed through a wet-forming route, whose exhibited excellent performance with a density of 0.26 g/cm3, stress strength of 15.83 MPa, interlayer bonding strength of 293.47 J/m2, and electrical breakdown strength of 6.88 kV/mm. In addition, the bulkpaper exhibited low dielectric constant and dielectric loss of 1.37 and 0.0043 (at 106 Hz), respectively. The activation strategies provided a feasible path for advanced bulkpaper enhancement.

Controlled therapeutic cholesterol delivery to cells for the proliferation and differentiation of keratinocytes.

The challenge of enhancing wound healing and skin regeneration, particularly in conditions like burns and diabetic wounds, necessitates innovative solutions. Cholesterol, often associated with cardiovascular diseases, plays vital roles in cellular functions, maintaining skin integrity and preserving the skin barrier. Here, we explore cholesterol's significance, its influence on keratinocytes, and its potential application in skin regeneration. The study utilizes electrospun polyimide (PI) fibers as a cholesterol carrier model and investigates its impact on HaCaT keratinocytes, marking the first time tracked cholesterol delivery from the scaffold into cells. We demonstrate that an optimal concentration of 0.7 mM cholesterol in the medium enhances cell proliferation, while higher concentrations have negative effects. Cholesterol-enriched scaffolds significantly increase cell proliferation and replicative activity, especially in a 3D culture environment. Moreover, cholesterol influences keratinocyte differentiation, promoting early differentiation while inhibiting late differentiation. These findings suggest that cholesterol-loaded scaffolds can have applications in wound healing by promoting cell growth, regulating differentiation, and potentially accelerating wound closure. Further research in this area will lead to innovative wound management and tissue regeneration strategies.

Fabrication of high performance polyimide fibers by dry-jet wet spinning technology

High-performance co-polyimide (co-PI) fibers derived from 3,3`4,4`-biphenyldianhydride (BPDA), p-phenylenediamine (p-PDA) and 2-(4-aminophenyl)-5-amino-benzimidazole (BIA) were prepared via the wet spinning and dry-jet wet spinning method, respectively. The distinctions between wet spinning and dry-jet wet spinning processes on the structures and properties of co-PI fibers were systematically investigated. The co-PI fibers prepared by dry-jet wet spinning exhibited smoother surface morphology and higher mechanical properties than those of co-PI prepared by wet spinning. Wide-angle X-ray diffraction (WAXD) results showed that the co-PI fibers prepared by dry-jet wet spinning exhibited highly oriented structure along the fiber direction along with a low degree of lateral packing order in the transverse direction. Small-angle X-ray scattering (SAXS) revealed that the radius, length, misorientation and internal surface roughness of the microvoids in the co-PI fibers prepared by the dry-jet wet spinning are lower than those in co-PI fibers prepared by wet spinning. Moreover, the effect of air layer height, as well as the heat treatment on the structure and properties of fibers during the dry-jet wet spinning process, was also studied. The tensile strength and modulus of co-PI fibers prepared by dry-jet wet spinning reached 2.72 GPa and 114.29 GPa, respectively, with an air layer height of 10 mm and a heat stretching temperature of 440°C.

Flexible metalized polyimide nonwoven fabrics for efficient electromagnetic interference shielding

Designing and fabricating efficient electromagnetic interference shielding materials has become a significant and urgent concern. Hence, a novel lightweight and flexible metallized polyimide nonwoven fabric is successfully prepared by polydopamine roughening, palladium-free activation of chloroplatinic acid, electroless nickel plating, and octadecanethiol corrosion-resistant treatment. As a result, the efficient construction of metallized surface on polyimide fibers facilitates the formation of multiple scattering for incident electromagnetic waves, leading to an excellent electromagnetic interference performance. More importantly, the strong binding force between nickel plating and polyimide fiber substantially improves the high/low-temperature resistance, endowing the composite with excellent stability and durability in electromagnetic interference performance. Meanwhile, the self-assembly modification of octadecanethiol on the surfaces of nickel plating effectively achieves the inhibition of metal corrosion. Additionally, the high electrical conductivity of metallized polyimide nonwoven fabric endows it with a rapid-responsiveness Joule heating performance, which makes it promising to become an efficient electromagnetic interference shielding material with a distinct competitive advantage in the cold environment.

Study on Dyeing Property of Polyimide Fiber by Ammonia Pretreatment

Study on Dyeing Property of Polyimide Fiber by Ammonia Pretreatment

In-situ constructing porous N-doped carbon skeleton with rich defects from modified polyamide acid to boost the high performance of Na3V2(PO4)3 cathode for full sodium-ion batteries

Generally, the transport of electrons and Na+ is seriously constrained in Na3V2(PO4)3 (NVP) due to intense interactions of V-O and PO bonds. Besides, polyamide acid (PAA) is hardly used in the sol–gel route due to insolubility. This work develops a facile liquid synthesis strategy based on modified PAA, achieving in-situ construction of a porous N-doped carbon framework with rich defects to improve the kinetics of NVP. The addition of triethylamine (TEA) reacts with carboxyls in PAA to achieve acid-base neutralization, turning PAA into polyamide salts with good solubility. The special morphology construction mechanism of this unique system was observed by ex-situ scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Specifically, PAA undergoes in-situ conversion into chain-like polyimide (PI) through a thermal polymerization mechanism during the pre-sintering process. Meanwhile, NVP precursors are evenly dispersed in the PI fibers, efficiently reducing the particle size. After the final treatment, the favorable porous carbon skeleton could be generated derived from the partial decomposition of PI, on which small active grains are in situ grown. The resulting N-doped carbon substrate contains rich defects, benefiting from the migration of Na+. Furthermore, the porous construction is conducive to alleviating the stress and strain generated by the high current impact, increasing the contact area between electrodes/electrolytes to improve the utilization efficiency of active substances. Comprehensively, the optimized samples exhibit a capacity of 82.1 mAh g−1 at 15C with a retention rate of 95.45 % after 350 cycles. It submits a capacity of 67.6 mAh g−1 at 90C and remains 52.2 mAh g−1 after 1500 cycles. Even in full cells, it reveals a value of 110.6 mAh g−1. This work guides the application of in-situ multiple modifications of polymers in electrode materials.

Ion transport regulation of polyimide separator for safe and durable Li-metal battery

Li-metal battery (LMB) gains enormous attentions because of its high energy and power density. However, the cycling stability of LMB is seriously harmed by the increase of internal temperature and Li-dendrite growth. The development of high-safety thermotolerant separators is urgently desired that can provide advantageous channels for rapid ion transport and simultaneously enable homogeneous Li+ fluxes to inhibit dendrite growth. With superior thermal and electrochemical stability, polyimide-based separator is a good alternative to commercial polyolefin-based separators, but prior design of either nanopores or micropores in polyimide-based separator usually met a dilemma. In this work, we report a polyimide sandwiched separator (denoted as s-PIF) with polyimide fiber (PIF) membrane coated by polyimide aerogels. Significant advancements in terms of mechanical property, electrolyte adsorption/retention and ion conductivity can be achieved for the s-PIF separator, compared with PIF separator. Moreover, the s-PIF separator can render a dendrite-free process of Li plating/stripping for 1400 h. Consequently, the LMB with s-PIF separator shows a remarkable stability with 80 % of its capacity retention after 3000 cycles at 10C.

Lightweight thermo- and heat-resistant composite materials based on polyimide foam

A prepolymer foaming composition based on 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride methyl ester and diamines: 4,4'-diaminodiphenylmethane and m-phenylenediamine for the production of high-temperature polyimide foam (PIF) is proposed. The p ossibility o f u sing P IF a s a b inder f or c omposite materials (foam composites) reinforced with carbon or organic fibers with low density (0.4–1.1 g/cm3) a s a result of foaming of the binder during the formation of the foam composite is shown. The density and mechanical properties of the foam composite can vary within a relatively wide range depending on the volume content of the fiber and air pores. The high glass transition temperature of 260°C, combined with the high thermal stability of carbon or polyimide fibers, contributes to the retention of the mechanical properties of such composites at elevated temperatures. The temperature of the start of mass loss of the foam composite must be at least 550°C, and it depends on the type of fibrous material. The combination of the excellent thermal and mechanical properties of lightweight PIF composites, together with the exceptional fire resistance of polyimide materials, may provide new applications in advanced aircraft and shipbuilding technologies.

Numerical modeling of the carbonization of polyimide fibers in a cylindrical furnace

Carbon fiber is widely used as a reinforcing material in polymer composite such as carbon fiber reinforced plastic (CFRP) due to its high specific strength, elastic modulus and lightweight. The majority of the industrial carbon fiber is produced from synthetic precursor polymer such as polyacrylonitrile (PAN), pitch and polyimide. While relatively many studies have been published for the carbonization of PAN, little studies have been found on the heat transfer during carbonization of polyimide precursors. In this study, we numerically analyzed the carbonization process of a polyimide (PI) precursor for carbon fibers in a lab-scale cylindrical furnace. Gas flow, temperature distribution and concentration profiles including the off-gases from the precursor fibers were included in the analyses. First, we established mathematical models for the off-gases behavior from the precursor fibers. The models were incorporated into computational fluid dynamics in order to find behavior of the mixture gas of the working nitrogen gas and the off-gases. And then, numerical simulation results using the model were obtained and compared to the experimental results to verify the model. Finally, we evaluated the application scalability of the established numerical model through changes in wall temperature and precursor fiber moving speed. The results showed that the model can be used to study the PI carbonization process in the industrial size carbonization furnace.

Scalable Preparation of Polyimide Sandwiched Separator for Durable High-Rate Lithium-Metal Battery.

The ever-growing demands for efficient energy storage accelerate the development of high-rate lithium-metal battery (LMB) with desirable energy density, power density, and cycling stability. Nevertheless, the practical application of LMB is critically impeded by internal temperature rise and lithium dendrite growth, especially at high charge/discharge rates. It is highly desired but remains challenging to develop high-performance thermotolerant separators that can provide favorable channels to enable fast Li+ transport for high-rate operation and simultaneously homogenize the lithium deposition for dendrite inhibition. Polyimide-based separators with superior thermal properties are promising candidate alternatives to the commercial polyolefin-based separators, but previous strategies of designing either nanoporous or microporous channels in polyimide-based separators often meet a dilemma. Here, a facile and scalable approach is reported to develop a polyimide fiber/aerogel (denoted as PIFA) separator with the microporous polyimide fiber membrane sandwiched between two nanoporous polyimide aerogel layers, which can enable LMBs with remarkable capacity retention of 97.2% after 1500 cycles at 10 C. The experimental and theoretical studies unravel that the sandwiched structure of PIFA can appreciably enhance the electrolyte adsorption and ionic conductivity; while, the aerogel coating can effectively inhibit dendrite growth to realize durable high-rate LMBs.

Bifunctional polyimide/ZIF8 composite nanofibrous membranes with controllable bilayer structure for bioprotective application and high-efficiency oil/water separation

A multi-use fibrous filter medium composed of an electrospun polyimide (PI) nanofiber layer and a functional zeolitic imidazolate framework-8 (ZIF8) nanofilm layer was successfully fabricated to cope with the complex environmental pollution issues. The nanofilm layer consists of the anti-microbial ZIF8 converted from non-toxic zinc oxide (ZnO) nanocoating on PI fibers. One-step magnetron sputtering is utilized to deposit the ZnO nanocoating for the sake of desired functionality conformally onto the PI nanofibrous membrane without sacrificing its bulk structure and mechanical performance. The as-prepared PI/ZIF8 nanofibrous filter medium showed conspicuous biocidal efficacy and excellent interception ratio against gram-negative Escherichia coli (>99.9%) and gram-positive Staphylococcus aureus (>99.9%) within 20 min contact. Besides, compared with commercial media, the bilayer PI/ZIF8 fibrous medium showed exceptional thermal-wet comfortability due to the high porosity that could realize effective heat and humidity conduction. Moreover, the PI/ZIF830 NFM still present a high filtration efficiency of 99.6% towards PM0.3 even after treated at 300 °C for 1 h. Furthermore, the PI/ZIF830 NFM with a fiber basis weight of 1.8 g/m2 was endowed with a permeate flux of 17,279.2 L/m2/h and a high oil/water separation efficiency of > 99.6% because of the hydrophobicity and superoleophilicity. We envision that the antimicrobial, thermal-wet comfort, multi-use fibrous membrane will serve as a core-medium of environmentally-friendly platform for bioprotective equipment against future pathogen threats or oily wastewater treatment.

Investigation of the mechanical properties of polyimide fiber/polyamide 12 composites printed by Multi Jet Fusion

ABSTRACT Multi Jet Fusion (MJF) has attracted extensive attention because of its ability to print support-free complex structures. However, the mechanical properties of MJF-printed polymer parts are still unsatisfactory for certain industrial requirements. Herein, by leveraging the fibre reinforcement effect and high specific strength of polyimide (PI) fibres, this work developed PI/polyamide 12 (PA12) composites with largely enhanced mechanical performance via MJF. Specifically, the tensile strength and modulus were increased by 43% and 42%, and the flexural strength and modulus were improved by 39% and 46%, respectively, compared to those of the neat PA12 parts. Furthermore, the incorporation of lightweight PI fibres endowed the composites with high specific tensile strength (67.60 kN·m/kg) and specific flexural strength (93.70 kN·m/kg), which are superior to those of MJF-printed PA12 composites reinforced with other fibres. This work provides new insights into enhancing the mechanical performance of lightweight parts printed by MJF and other powder-based techniques.

KH550‐SiO2/polyimide insulating paper preparation and characterisation

AbstractOil‐paper insulation material is an essential component for oil‐filled transformers, and polyimide (PI) insulation paper is a novel material in the field of electricity. The improvement of insulation class for insulation paper has gained significant attention in recent years. In this study, SiO2 nanoparticles were modified with a silane coupling agent (KH550), and the KH550‐SiO2 was added to the fibre membrane through in situ polymerisation. The chemical composition and microcosmic characteristics of the PI porous fibre membrane were characterised using FT‐IR and SEM FT‐IR and SEM. Consequently, the dielectric constant of the composite paper was reduced to 2.3 upon adding 3 wt% of KH550‐SiO2, and the dielectric strength reached its maximum value of 85 kV/mm. The results demonstrate that the insulation performance of the KH550‐SiO2/PI composite was significantly improved due to the incorporation of nano‐SiO2. This establishes an efficient approach for achieving excellent electrical and thermal properties in practical applications using the KH550‐SiO2/PI fibre membrane.

Theoretical and experimental study of CO2 removal from biogas employing a hollow fiber polyimide membrane

In the present work, the efficient removal of CO2 from CH4 for biogas upgrade is investigated, employing a commercial polyimide (PI) membrane (UBE Industries Ltd., Japan). The goal is to meet the requirements of high purity biomethane (>95%) for effective energy use (e.g., by connecting the CH4-rich gaseous stream into the natural gas grid) with simultaneous CO2 capture, for potential reuse. The separation process is studied experimentally employing a commercial hollow fiber polyimide membrane module at laboratory scale conditions, while mathematical process models of various complexity in terms of the flow conditions are employed and compared with the experiments. The results demonstrate that, among the different flow models, the crossflow model is in much better agreement with the experimental results and can be further employed to design more complex membrane module configurations, such as two- and three-stage processes, recycle, etc.

Self-assembly-dominated hierarchical porous nanofibrous membranes for efficient high-temperature air filtration and unidirectional water penetration

Increasingly-severe air pollution problem dominated by various air pollutants makes the development of air filtration materials a hotspot. A multi-functional air filter with high efficiency and high temperature resistance was produced using a co-electrospinning method combined with subsequent impregnation treatment. Herein, Cu-MOF was assembled onto polyimide (PI) nanofibers to construct a hierarchical porous structure. Diamine monomers containing amide bonds were copolymerized in the PI skeleton to activate the surface sluggishness of PI. β-cyclodextrin (β-CD) was used as PI fiber inducer to achieve the self-assembly of Cu-MOF crystals via hydrogen bonding. On one hand, PI/CD-MOF nanofiber filter possesses an excellent PM0.3 filtration efficiency (99.85%) and a low pressure drop (136 Pa), which are attributed to high specific surface area of the nanofibrous filter. On the other hand, the filter demonstrates the optimal performance in terms of CO2 adsorption due to the outstanding open metal sites of Cu-MOF. In particular, Janus double-layer composite nanofibrous membrane, which consists of PI/CD-MOF and PI membranes, has unique unidirectional water permeability performance and long-term filtration stability. Base on the above studies, this preparation strategy could provide idea for the development of multifunctional air purifiers.

Highly Hydrolysis-Resistant Polyimide Fibers Prepared by Thermal Crosslinking with Inherent Carboxyl Groups

Highly Hydrolysis-Resistant Polyimide Fibers Prepared by Thermal Crosslinking with Inherent Carboxyl Groups

Coatings Made by Atomic Layer Deposition for the Protection of Materials from Atomic Oxygen in Space

Atomic Layer Deposition (ALD) has been investigated for the possible protection of various materials against atomic oxygen (ATOX) at ESTEC Materials and Electrical Components Laboratory facility. ALD is a conformal coating process, that can be used to apply ultra-thin films of metal oxides on various materials, that may have a sophisticated three-dimensional shape, such as the internal and external components of satellites. The challenge with metal oxides on soft and/or flexible surfaces arises from the brittle nature of these ceramic films if their thickness exceeds 30 nm. Different substrates, including silicon, Printed Circuitry Board (PCB), polyimide, and Carbon Fibre Reinforced Polymers (CFRP) were coated by ALD with 20 nm thick metal oxide films at 125 °C, then exposed to ATOX and characterized by photographing, reflectance measurement and scanning electron microscopy (SEM). The studies showed good performance of protective films prepared by ALD on polymer substrates, which suggests that the nanometer-scale coatings can improve the lifetime of these materials at low Earth orbit, where they are inevitably exposed to ATOX. In contrast, the uncoated substrates suffered near-surface damage after exposure to ATOX, which resulted in microscopic features on their surface that were visible in SEM. Damage caused by ATOX to the uncoated substrates was also visible in photographs and observable in reflectance studies. In the latter case, the changes in the reflectance spectrum were caused by the change of surface morphology and/or chemical and elemental composition due to corrosion by ATOX.

Continuous Surface Metallization of Polyimide Fibers for Textile-Substrate Electromagnetic Shielding Applications

Continuous Surface Metallization of Polyimide Fibers for Textile-Substrate Electromagnetic Shielding Applications

Heterogeneous Waterborne Polyurethane Composite with Alternating Electromagnetic Layers for Absorption-Dominated Electromagnetic Interference Shielding.

Flexible waterborne polyurethane (WPU) electromagnetic interference (EMI) composites of heterogeneous alternating multilayer structure with conductive gradient were fabricated through the layer-by-layer stacking and hot-pressing methods. Combining the synergetic electromagnetic loss and interface polarization loss formed by the selective distribution of metallized chopped polyimide fiber (PI@Ni/Cu/Ni), reduced graphene oxide (rGO), and magnetic Fe3O4 fillers, as well as multilevel electromagnetic wave propagation paths, the penetrating microwaves would undergo a particular "absorption-reflection-reabsorption" process in the composite. The asymmetric multilayer WPU composite with an absorption-dominated shielding feature exhibits a high EMI shielding effectiveness (SE) of 53.90 dB and an A value of 0.56. Moreover, the multilayer WPU composite maintains excellent integrity through repeating bending, long-time soaking, and burning tests. This work provides a viable strategy for the design of absorption-dominated EMI shielding material with controllable and stable performance that is befitting for next-generation advanced electronic products.