High-strength Polyimide Research Articles

Preparation and thermal insulation properties of lightweight high-strength polyimide aerogels containing benzoazole structures

Polyimide (PI) aerogels, serving as thermal insulation materials in extreme environments, stand out for their exceptional high temperature stability and superb thermal insulation properties, rendering them ideal for aerospace, transportation, and specialized equipment industries. However, conventionally synthesized PI aerogels suffer from significant drawbacks in mechanical properties and thermal stability, limiting their practical applications. To overcome this challenge, we successfully synthesized polyimide aerogels using biphenyl-3,3,4,4′-tetracarboxylic dianhydride (BPDA), 5-amino-2-(4-aminophenyl)benzimidazole (PABZ), and 5-amino-2-(4-aminophenyl)benzoxazole (APBO) followed by supercritical carbon dioxide drying. These synthesized PIs exhibit remarkable thermal stability, with high thermal weight loss temperatures (Td5 %=595–611℃) and high glass transition temperatures. Additionally, these novel PI aerogels demonstrate exceptional thermal insulation properties, high specific surface area, and extremely small pore size. Furthermore, boasting a low dielectric constant (ε=1.72), these newly developed PI aerogels offer along with excellent mechanical properties, holding substantial promise for applications in the forthcoming generation of advanced aerospace and specialized equipment materials.

Preparation of High-Strength Polyimide Porous Films with Thermally Closed Pore Property by <i>In Situ</i> Pore Formation Method

Preparation of High-Strength Polyimide Porous Films with Thermally Closed Pore Property by <i>In Situ</i> Pore Formation Method

Polyhedral oligosilsesquioxane-modified boron nitride enhances the mechanical properties of polyimide nanocomposites.

A novel high-strength polyimide (PI) nanocomposite film was designed and constructed by the copolymerization of epoxidized polyhedral oligomeric silsesquioxane-modified hexagonal boron nitride and polyamic acid (PAA). The composite filler (EPPOSS@Gh-BN) was composed of silane coupling agent KH550 modified hexagonal boron nitride (Gh-BN) and epoxidized polyhedral oligomeric silsesquioxanes (EPPOSS), which improved not only the dispersion of the h-BN but also the effective interfacial stress transfer, leading to an enhanced mechanical strength of the resultant PI nanocomposite film of 114 MPa even with a slight EPPOSS@Gh-BN loading of 0.30 wt%, and the storage modulus was increased by more than 30% to 4 GPa compared to pure PI. Meanwhile, the PI/EPPOSS@Gh-BN nanocomposite has better heat transfer performance, higher hydrophobicity, lower dielectric properties, and higher heat stability than pure PI, and is therefore expected to provide an ideal platform for the development of highly flexible electronics in the future.

Preparation of high-strength polyimide membranes capped by ionic liquids

In this study, we firstly used 1-carboxyethyl-3-methylimidazolium ionic liquid as a capping agent to terminate a binary linear polyimide containing different groups such as ether bonds, carbonyl groups, and fluorine, and prepared six kinds of polyimides capped with ionic liquids (IL-PI). The mechanical properties of the polyimide membranes capped with ionic liquids were higher than those of the uncapped polyimide membranes. The elastic modulus of polyimide membrane from 1,3-bis (4-aminophenoxy) benzene (BPDA) and 3,3′4,4′-benzophenone tetracarboxydianhydride (BTDA) by using ionic liquid as the end capping agent (IL-BPDA-BTDA) was 2012 MPa, which is about 70 times higher than that without the end capping agent. In a TG test, all polyimides capped by ionic liquids showed good thermal properties. The residual amount of the polyimides was more than 40% at 1000 °C, which was higher than the other uncapped polyimides. In conclusion, polyimide membranes with high temperature resistance and high mechanical strength were prepared through an ionic liquid termination method.

Covalently linked polydopamine-modified boron nitride nanosheets/polyimide composite fibers with enhanced heat diffusion and mechanical behaviors

Polymer fibers with high tensile strength and high thermal conductivity (k) are attractive in next-generation thermoregulating textiles, wearable electronic devices and so on. However, most polymeric fibers usually have a low thermal conductivity below 0.5 W m−1 K−1, hardly satisfying the high requirements for thermal management. Herein, we report an effective approach to achieve a highly thermally conductive and high-strength polyimide (PI) composite fibers containing the polydopamine modified boron nitride nanosheets (PDA@BNNS). The uniform dispersion of nanofiller, covalent adhesion of PDA@BNNS to PI matrix and highly aligned PDA@BNNS network are successfully realized during in-situ polymerization, wet-spinning and post hot-drawing process. Thus, significant improvements in the heat diffusion behavior and mechanical property for PI/PDA@BNNS composite fibers are achieved. The incorporation of a very low content of PDA@BNNS (~0.5 wt%) results in a 27% increase in thermal conductivity for the PI/PDA@BNNS-0.5 composite fiber. An optimum thermal conductivity of 3.44 W m−1 K−1 for the composite fiber is obtained with 10 wt% nanofiller addition, and meanwhile, the tensile strength and modulus approach 1.8 GPa and 100.7 GPa, respectively, far exceeding most of the BNNS containing composite fibers. Additionally, these composite fibers are scalable and weavable, making them good candidates for the future advanced functional textiles or as the reinforcement in thermally conductive composites applications.

Polyimide capping layer on improving electrochemical stability of silicon thin-film for Li-ion batteries

Silicon (Si) is a promising anode material for LIBs due to its high theoretical gravimetric capacity of 3570 mAh g−1, which is about ten times higher than that of graphite. However, the large volume expansion of Si during lithiation gives rise to non-trivial mechanical challenges and constraints which hinder widespread commercial adoption. In particular, electrode cracking and delamination destroy the intrinsic electrical connectivity in the Si electrodes, leading to rapid capacity degradation upon cycling. Herein, we demonstrate a novel approach of capping Si thin-film electrodes with a high strength polyimide by electro-spraying to overcome the pulverization and mechanical issues during cycling. The polyimide layer provides mechanical support to the Si thin-film and maintains its capacity during cycling, with a high capacity of 2610 mAh g−1 at 100 mA g−1 and no capacity loss after 300 cycles at 3500 mA g−1. Furthermore, in situ dilatometry tests reveal that the polyimide capping layer enables reversible electrode thickness change during lithiation and de-lithiation, thus improving the cycling performance. This work provides a practical manufacturing strategy for commercializing silicon-based electrode films.

Dielectric and mechanical properties of polyimide composite films reinforced with graphene nanoribbon

Graphene nanoribbon (GNR) was introduced into in the polyimide (PI) composite films. The effects on dielectric and mechanical properties of PI/GNR composites were investigated. Results show that the dielectric and mechanical properties of the composite films are significantly enhanced compared to pure PI. This can attribute the excellent dispersion of and the strong interfacial interaction between GNR and the PI matrix. Tensile strength of PI/GNR composite films shows a first increasing and then decreasing trend with increased GNR content. With 0.1wt% loading, the tensile strength is increased from 120.1MPa to 166.7MPa, and the dielectric constant of PI/GNR composite film is decreased from 3.6 to 3.1 compared to pure PI, respectively. The success of this preparation is believed to afford new avenue for the development of high strength polyimide based composites.

Lightweight, Conformal Antennas for Robotic Flapping Flyers

Using wings on small flying robots for embedded antennas can provide a flexible and lightweight solution for communications from these platforms. The fabrication of ultra-lightweight, high-strength polyimide nanopaper fabric from which the wing is built is outlined. Such materials can be used to build multilayer, lightweight electronics in a variety of other situations. After outlining the fabrication of the nanopaper, designs for two different antenna-embedding techniques are presented. First, a simple embedded wire antenna is fabricated and measured, followed by a more-complex printed antenna design. Each process is outlined and trade-offs are presented. Both designs worked well, and can be adapted for use in other similar scenarios.

High strength polyimide fibers with functionalized graphene

Graphene possesses unprecedented physical and chemical properties and has been thought to be ideal filler for reinforcing fibers' mechanical properties. However, graphene is difficultly dispersed in polymer which severely restrict to prepare high-strength and high-modulus composites. In this work, we report an effective method to fabricate a kind of organ-soluble polyimide (PI)/graphene composite fiber using in situ polymerization. Graphene oxide (GO) is modified by 4,4′-diaminodiphenyl ether (ODA) to obtain the GO-ODA nanosheets which exhibit excellent dispersibility and compatibility with the organ-soluble PI matrix. WAXD results show that these 2D nanosheets have a significant influence on the crystallization, aggregation or assembly behaviors of the polymer chains. The PI/graphene composite fiber containing 0.8 wt% of GO-ODA presents a tensile strength of 2.5 GPa (1.6 times higher than the pure PI fiber), and tensile modulus of 126 GPa (223% raises compared with pure PI fiber). Furthermore, the incorporation of graphene significantly improves the glass transition temperature and thermal stability of the composite fibers. Thanks to the excellent hydrophobic properties of graphene, the hydrophobic behavior of the composite fibers is greatly improved. This effective approach shows a potential application in fabricating multifunctional polymer-based composite fibers.

High‐Strength Mats from Electrospun Poly(p‐Phenylene Biphenyltetracarboximide) Nanofibers

High-strength polyimide mats have been formed from electrospun nanofibers of a rigid-rod-like poly(p-phenylene biphenyltetracarboximide) (see Figure). Non-woven mats of aligned nanofibers have a tensile strength of 664 MPa and a tensile modulus of 15.3 GPa. These high-performance electrospun nanofibers with excellent mechanical properties and heat resistance are expected to be useful for applications such as protective clothing and heat-resistant filters.

601 高強度ポリイミドの耐アルカリ性向上(機械材料・新素材I,オーガナイズドセッション,人体のコンピュータモデルの作成とその応用,特別講演)

601 高強度ポリイミドの耐アルカリ性向上(機械材料・新素材I,オーガナイズドセッション,人体のコンピュータモデルの作成とその応用,特別講演)

Development of Polyimide Ablators for NIF: Analysis of Defects on Shells, a Novel Smoothing Technique and Upilex Coatings

Over the last three years, LLNL has developed polyimide vapor deposition technology suitable for mandrel overcoating and fabrication of polyimide capsules. Agitated mandrels were overcoated with 4,4’-oxydianiline and pyromellitic dianhydride, and the PMDA/ODA coating was thermally converted to polyimide by heating to 300°C. Shells from this process did not meet smoothness requirements specified by the target designs for the National Ignition Facility (NIF). The defects and the possible mechanism(s) for defect generation were analyzed, and it was determined that surface roughness was the result of shell-pan interaction(s). A post-processing, shell smoothing technique was also developed which simultaneously levitates the shell while exposing it to solvent vapor. Efforts to form Upilex™, a high strength polyimide, using vapor deposition will also be discussed.