Polyimide Foams Research Articles

Structural Optimization of Polyimide Foam via Composition with Hyperbranched Polymer Modified Fluorinated Carbon Nanotubes

Structural Optimization of Polyimide Foam via Composition with Hyperbranched Polymer Modified Fluorinated Carbon Nanotubes

Fabrication of rigid polyimide foams by adopting active crosslinking strategy

Rigid polyimide foams (PIFs) with excellent mechanical and thermal properties were fabricated by thermal foaming of active cross-linkable units terminated polyester ammonium salts (PEAS) precursor powders. The active cross-linking strategy was realized by breaking CC bonds in maleic anhydride under heating treatment. Results showed that the formation of cross-linked structure before complete imidization effectively resisted matrix shrinkage and endowed PIFs with outstanding mechanical properties. The room temperature compressive strength and modulus of PIFs with four repeating units reached as high as 2.34 and 56.1 MPa, respectively. Moreover, the PIFs exhibited excellent thermal properties with onset decomposition temperatures ranging from 490 to 550 °C and the glass transition temperatures exceeding 290 °C. The PIFs displayed better thermal insulation, and the values of thermal conductivity fell within a range of 0.056–0.090 W m−1 K−1, which demonstrates potential application as high temperature resistant structural materials in aerospace and energy sectors.

High-performance porous carbon foams via catalytic pyrolysis of modified isocyanate-based polyimide foams for electromagnetic shielding

High-performance porous carbon foams via catalytic pyrolysis of modified isocyanate-based polyimide foams for electromagnetic shielding

Mechanically flexible polyimide foams with different chain structures for high temperature thermal insulation purposes

Mechanically flexible polyimide foams (PIFs) with exceptional high temperature thermal insulation properties were fabricated by microwave-assisted foaming and post thermal imidization process, using polyester ammonium salt (PEAS) precursor powders which consisted of different molecular chain structures as the derivatives. A comparison of foaming behavior, pore morphology, mechanical and thermal insulation properties between PIFs prepared with mono-dianhydride and copolymerized dianhydride structures was systematically studied. Results showed that the optimum foaming temperatures of PEASs was in the range of 85–150 °C, which correlated with the volatilization of solvents such as H2O, tetrahydrofuran and methanol. The introduction of copolymerized dianhydride structure altered the chain rigidity and melt viscosity of PEAS, which improved the cellular structure and mechanical flexibility of PIFs. Moreover, the micron-scale cellular structure of PIFs was determined by melt viscosity, chain rigidity, volatile content and foaming temperatures. The PIFs exhibited low apparent densities (25–30 kg/m3), high open cell rate (95–97%) and mechanical flexibility (compression/release recover rate: 96–99%). All PIFs possessed exceptional thermal stability and thermal insulation properties which can be targeted for thermal insulation applications in the fields of aerospace, transportation, and microelectronics among others.

Ultralight and Highly Resilient Boron Nitride Nanosheet/Polyimide Foams for Energy Harvesting and Sensing

The application of highly superelastic foamlike materials has gradually expanded to various high-end areas, such as filtration purification, mechanical power generation, and energy storage, showing their considerable and expected prospects. In this paper, facile freeze-drying technology combined with a gradual thermal-imidization process was employed to prepare a series of boron nitride nanosheet (BNNS)-filled polyimide (PI) composite foams. These foams can exhibit excellent mechanical properties, including their cyclic stability for considerable cycles under long compressive loading–unloading processes, and their relatively low irreversible deformation. After 10000 cycles at the compression strain of 60%, the total strain loss of the composite filled with 12 wt % is only 14%, which is 2/3 that of pure PI foam. Based on these excellent mechanical characteristics, the foam composites exhibit well a compression-driven triboelectric performance. The effects of BNNS content, compression strain, and rate on the triboelectric properties of the composites were studied in detail. We found that a higher compression strain and compression rate will lead to stronger electrical signals. More significantly, on the basis of the one-to-one relationship between electrical signal and compressive deformation, BNNSs/PI foam will likely be used in the field of control sensing. Finally, the electrical generation device based on composites was used in an insole and keyboard to transform mechanical energy generated by human movement into electrical signals.

Flexible and mechanically robust polyimide foam membranes with adjustable structure for separation and recovery of oil-water emulsions and heavy oils

Oil-water separation materials have been widely studied, however, these materials are mainly used to separate light oil-water mixtures, and the application of heavy oil separation and recovery is rarely involved. It is urgent to develop novel multi-functional oil-water separation materials, especially for the separation membrane for heavy oil. Herein, mechanically robust fiber-reinforced fluorinated polyimide foam membranes (FPIFMs) with adjustable multistage pore structure and high oil-water selectivity were prepared by freeze-drying and surface modification. FPIFMs exhibit high tensile strength of 3.80 MPa with the synergistic effect of PI fibers and PAA. Besides, the macro void structure of the foam membrane can be precisely adjusted to achieve the separation of different types of oil-water mixtures, oil-water emulsions, especially the separation and recovery of heavy oil. The results show that the foam membranes can separate light oil (26935L·m−2·h−1), oil-water emulsion (364L·m−2·h−1) and heavy oil (30L·m−2·h−1) under gravity. This stable, highly flexible, highly efficient and reusable foam membrane is an attractive option for oil spill treatment and wastewater purification.

Anisotropic all-aromatic polyimide aerogels with robust and high-temperature stable properties for flexible thermal protection

• Unidirectional anisotropic PIAs have been prepared by freeze-drying. • The PIA shows excellent thermal stability and stable mechanical behavior. • The u -PIA-6 exhibits great strength, which is over twice as high as that of the TEEK-HH at 177 °C with a similar density. • The u -PIA shows great thermal insulation properties in anisotropic. Polyimide aerogels (PIAs) are the new type of high-performance lightweight material that combines the excellent thermal and mechanical behavior of polyimides with the highly porous and lightweight properties of aerogels. PIAs can meet the increasing material requirements of high-tech fields such as the aerospace and transportation industries. This study reports a series of all-aromatic anisotropic polyimide aerogels (p-phenylenediamine (PDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA)) with unprecedented behavior. These PIAs were synthesized using a random or unidirectional freeze-drying method followed by thermal imidization of the precursor solution. Their mechanical and thermal conductivity performance were anisotropic ( u -PIA-8 strength: 1.86 and 0.14 MPa, thermal conductivity: 62.9 and 50.1 mW·m −1 ·K −1 along the axial and radial direction, respectively). Furthermore, the PIAs possessed excellent compression behavior in a wide temperature range from 25 °C to 316 °C, with a compressive strength over twice that of the commercial polyimide foam TEEK-HH ( u -PIA-6 strength: 0.83 and 0.32 MPa at 177 and 316 °C, TEEK-HH strength: 0.31 MPa at 177 °C). These aerogels also demonstrated good thermal insulation performance after being held at 300 °C for 20 min ( u -PIA-8: 76.3 °C at 25 mm). These highly anisotropic aerogels exhibit flexible thermal protection properties that extend the potential use of PIAs to applications such as high-temperature-resistant rocket fairings, sandwich structures, and arc-shaped structures for aerobats or the automobile industry.

Modified hollow glass microsphere isocyanate-based polyimide foam composite with improved mechanical and thermal insulation properties

In this work, hollow glass microspheres (HGM) were introduced into the polyimide matrix as an effective reinforcement filler to improve the mechanical and thermal insulation properties of the polyimide foams (PIF). The HGM was surface-modified with the silane coupling agent to enhance the interfacial compatibility with PIF. Experimental results revealed that the average cellular diameter of PIF decreased obviously with the addition of the modified HGM (M-HGM). The apparent density of foams also increased from 15.85 to 18.34 kg/m3 when the M-HGM combination was changed from 0 to 12 percent (wt.%). Compared with the pure PIF, the composite foams added 8 wt.% M-HGM showed high compression strength (65 kPa) and compression modulus (1147 kPa), resulting in a distinct enhancement in mechanical properties. Furthermore, the addition of M-HGM filler also improved the thermal insulation performance of PIF, which exhibited the minimum thermal conductivity of 29.48 mW·m−1·K−1 with 8 wt.% M-HGM. Thus, considering the improved mechanical and insulation properties of the prepared PIF, it could be a promising candidate for the high temperature-resistant thermal insulating applications.

Combining Microwave‐Assisted Foaming and Post Curing Process to Prepare Lightweight Flexible Polyimide Foams for Thermal Insulation Applications

AbstractLightweight flexible polyimide foams (PIFs) with different rigid‐flexible molecular structure networks are prepared by microwave‐assisted foaming of polyester ammonium salt (PEAS) precursor powders, followed by post curing process to complete final imidization. The optimum foaming temperatures of PEAS precursors range from 85 to 135 °C, and the melting rate of PEAS is adjusted to meet the volatile releasing rate to fabricate PIFs. Results show that PIFs with nearly fully open cell rate (99.99%), micron pore sizes (400–500 µm), and micro/nano multiscale structures exhibit excellent mechanical flexibility and elasticity. The prepared PIFs demonstrate exceptional thermal stability and heat resistance in both dynamic and static environments. The PIFs possess low thermal conductivity and superior thermal insulation properties that demonstrate potential applications in high‐tech fields such as aerospace, marine use, and microelectronics among others.

Achieving multiband compatible and mechanical tuning absorber using edge topological defect-induced graphene plasmon

Graphene has been shown to be a high-performance microwave-absorbing material with broadband potential. However, simultaneous realization of multiband compatible strong absorption is still a challenge. In this study, graphene rich in edge topological defects is successfully synthesized, and the effect of defect density on electromagnetic parameters has been investigated. Electrons (π electrons, π+σ electrons) located at edge defects alter the loss paths and plasma absorption frequencies of the graphene aerogels. These improvements in electrical properties give the graphene aerogel a more coordinated impedance matching and attenuation capability, allowing it to achieve strong absorption in multiband (S, X, Ku band) simultaneously. In addition, a mechanically tunable multimode absorber can be further realized by incorporating porous polyimide foam. The strong absorption (>99.9%) of a wide range of variable bands (S, C, X, and Ku bands) can be flexibly adjusted by stress cycling of piezo resistive foam. In addition, self-cleaning, high temperature resistance, and simple processability are expected to deliver solutions for the communication and Internet of Things engineering.

Polyimide foam composites with nano-boron nitride (BN) and silicon carbide (SiC) for latent heat storage

Leaching and instability in wax-based phase change materials (PCMs) are serious application problems. Herein, we developed paper-like (~ 100 µm) flexible, composite PCMs by hydraulic compression of 1-cm-thick polyimide foams between an aluminum foil and a (nano) ceramic composite Parafilm®. An unfilled PCM film placed between the foam and the aluminum surface ensured strong adhesion between the collapsed foam and the metal. Different concentrations of nano-BN and micro-SiC particles were compounded into Parafilm® in order to optimize the thermal performance. Based on infrared imaging, the monoliths containing 30 wt% micro-SiC outperformed all other systems including BN/SiC hybrids. The next best thermal performance was observed with the 60 wt% nano-BN composite. Due to compression, the cellular structure of the polyimide foams collapsed irreversibly while being impregnated by the PCMs from both sides. High-k fillers improved impregnation into the collapsed foam and enabled excellent shape stability and leakage prevention.Graphical abstract

Research on Acoustic Absorption Properties of Aramid Honeycomb Composite Material Reinforced by Polyimide Foam

To endue sound absorption behavior for aramid honeycomb core (ARHC), isocyanate‐based polyimide foam (IBPIF) with excellent thermal insulation and acoustic properties produced by a new formulation of foaming slurry is filled into ARHC by the free foaming route. As a core factor to adjust the cellular structure of IBPIF, the effect of water dosage on the acoustic behavior of IBPIF and IBPIF filled ARHC (IBPIF/ARHC) is studied, and the optimal formula to produce IBPIF/ARHC is filtered out. Results suggest that water dosage effectively regulates the cellular structure of IBPIF. When water dosage is 7.2 g, IBPIF has a large windows opening rate, which plays a positive role in sound absorption performance. IBPIF/ARHC‐3 has the best sound absorption property, which possesses a maximum sound absorption coefficient (α) of 0.9 at 1500 Hz. Its average α increases to 0.78 and shows an increase of 680% compared to ARHC. Meanwhile, the density of IBPIF/ARHC is only about 59 kg m−3. In 300–600 Hz range, IBPIF‐3 and ARHC show obvious synergy effects in sound absorption behavior. The average α of IBPIF‐3 and ARHC is only 0.3 and 0.06, respectively, and that of IBPIF/ARHC‐3 reaches up to 0.42. The thermal insulation performance of ARHC is also improved, and thermal conductivity decreases from 0.067 to 0.047–0.049 W (m K)−1.

Large size translucent wood fiber reinforced PMMA porous composites with excellent thermal, acoustic and energy absorption properties

From the perspective of the comprehensive requirements of building materials, this study introduces a foaming process into wood fiber transparent wood to prepare wood fiber reinforced Polymethyl methacrylate (PMMA) porous composites. The material not only further optimizes the mechanical and thermal properties of transparent fiber wood, but also improves the acoustic properties. It also has a characteristic of translucency. At the same time, the preparation process is simple, which has many advantages to be used as potential energy-saving building materials. According to the experimental results, the thermal conductivity is only about 40% of that of the common transparent wood. The sound absorption coefficient can reach 0.6, which is equivalent to that of polyimide foam. The mechanical compressive strength can reach 9 MPa, and the energy absorption performance is excellent. The yield stress platform is long, and the energy absorption efficiency can reach higher than 90%, which is better than currently available metal foams.

Fabrication of Rigid Polyimide Foams with Superior Compressive Properties

Fabrication of Rigid Polyimide Foams with Superior Compressive Properties

A simple and green strategy for preparing flexible thermoplastic polyimide foams with exceptional mechanical, thermal-insulating properties, and temperature resistance for high-temperature lightweight composite sandwich structures

Polyimide (PI) foams possess excellent mechanical properties, high-temperature resistance, and other unique properties, which facilitate impact in aerospace, automotive, and microelectronics industries. However, when they are used as lightweight insulation structural layers for high-temperature carbon fiber reinforced composites, improvement in thermal-insulating properties and temperature resistance of PI foams without compromising the flexibility in extreme environments is a challenging task. In this study, the flexible blocks were linked into rigid polymeric structures to fabricate a thermoplastic structure through a simple aqueous strategy to construct hydrogen-bonding networks. Thus, with a low shrinkage of 8.42%, an ultrahigh compressive modulus of 11.17 MPa, and a specific modulus of 81.03 MPa cm3 g−1 was successfully achieved. Benefitting from the formation of ultra-strong network backbones, foams showed excellent thermal-insulating properties and temperature resistance. The robust porous material with thermal-insulating properties (0.0481 W m−1 K−1) exhibited a compression modulus of 4.21 MPa after heat treatment at 300 °C and maintained 91% strength retention, thus it can be used as lightweight heat-insulation composite sandwich structures up to 300 °C. The copolymer foam obtained by using 30 mol% flexible blocks reserves its high flexibility undergoing only 10% dimensional changes after 40,000 compression-release cycles. The lightweight thermoplastic PI foams with flexibility, thermal-insulating properties, and temperature resistance can be used for high-temperature lightweight composite sandwich structures in aeronautics and space exploration.

The synthesis and properties of isocyanate-based polyimide foam composites containing MWCNTs of various contents and diameters.

Polyimide foams (PIFs) were synthesized using in situ polymerization from poly((phenyl isocyanate)-co-formaldehyde) (PAPI), pyromellitic dianhydride (PMDA), and multi-walled carbon nanotubes (MWCNTs) (0.05, 0.1, 0.2, 0.4, and 0.6 wt%) functionalized with –OH; the diameters were 10–20 nm, 20–30 nm, and >50 nm. The morphology, mechanical properties, and flame retardancy of the composites made from MWCNTs with different contents and diameters were studied. The effects of different contents of MWCNT on the properties of composites were compared. SEM results show that the pore morphology of PIF was not damaged when the content of the MWCNTs was low due to crosslinking between MWCNTs and amide bonds. When the content of the MWCNTs was high, the vacuoles of PIF became large and uneven. Compared to pure PIF, mwCNT-1 (0.2% MWCNT content) significantly increased the compressive strength (330%) and compression modulus (210%) of PI. Due to the significant thermal stability of PIF/MWCNTs, the degradation temperature of PIF/MWCNT-1 (0.2% MWCNT content) was increased from 302 °C to 321.5 °C upon addition of MWCNTs. The effects of different diameters of MWCNTs on the morphology and properties of the PIF/MWCNT composites were also compared. The morphology, thermal stability, and mechanical properties of the composites containing smaller MWCNTs were higher than those of composites containing larger MWCNTs. This is because MWCNTs act as nucleating agents to promote the formation and growth of bubbles. Smaller diameters of MWCNTs lead to higher MWCNT contents in the unit volume and more nucleation points of MWCNTs in the PIF. An increasing MWCNT diameter leads to a gradually decreasing number of bubbling nucleation centers. The LOI of PIF/MWCNTS increased with increasing MWCNT due to the nitrogen heterocyclic interaction between the PIF and MWCNTS. The diameter of MWCNTS had only a minor effect on the flame retardancy.

Closed-Cell Rigid Polyimide Foams for High-Temperature Applications: The Effect of Structure on Combined Properties.

Closed-cell rigid polyimide foams with excellent thermal stability and combined properties were prepared by thermal foaming of a reactive end-capped polyimide precursor powder in a closed mold. The precursor powder was obtained by thermal treatment of a polyester-amine salt (PEAS) solution derived from the reaction of the diethyl ester of 2,3,3′,4′-biphenyl tetracarboxylic dianhydride (α-BPDE) with an aromatic diamine mixture of p-phenylenediamine (PDA) and 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) in the presence of an end-capping agent (mono-ethyl ester of nadic acid anhydride, NE) in an aliphatic alcohol. The effect of polymer mainchain structures on the foaming processability and combined properties of the closed-cell rigid polyimide foams were systematically investigated. The polyimide foams (100–300 kg/m3) with closed-cell rates of 91–95% show an outstanding thermal stability with an initial thermal decomposition temperature of ≥490 °C and a glass transition temperature of 395 °C. Polyimide foams with density of 250 kg/m3 exhibited compression creep deformation as low as 1.6% after thermal aging at 320 °C/0.4 MPa for 2 h.

Carbonization of Graphene-Doped Isocyanate-Based Polyimide Foams to Achieve Carbon Foams with Excellent Electromagnetic Interference Shielding Performance.

Lightweight carbon foams with excellent electromagnetic interference (EMI) shielding performance were prepared by carbonization process, using isocyanate-based polyimide foams as carbon precursors. The influence of carbonization temperature and graphene-doping on the morphological, electrical and EMI shielding effectiveness (SE) of corresponding carbon foams was studied in detail. Results showed that the addition of graphene was beneficial to the improvement of electrical conductivity and EMI shielding performance of carbon foams. The electrical conductivity of carbon foams increased with the carbonization temperature which was related to the increase of graphitization degree. Collapse of foam cells was observed at higher carbonization temperatures, which was detrimental to the overall EMI SE. The optimal carbonization temperature was found at 1100 °C and the carbon foams obtained from 0.5 wt% graphene-doped foams exhibited a specific EMI SE of 2886 dB/(g/cm3), which shows potential applications in fields such as aerospace, aeronautics and electronics.

Mechanical properties of low‐density heat‐resistant polyimide‐based advanced composite sandwich panels

AbstractThis study presents low‐density heat‐resistant polyimide (PI)‐based advanced composite sandwich panels (HRACS) consisting of carbon fiber‐reinforced PI matrix thermoset and thermoplastic advanced composite laminates (outer faces) and PI foams (core materials). For the outer faces, thermoplastic composite laminates were prepared from poly (amic acid) ammonium salt precursor resin, and the thermoset was prepared from nadic anhydride (NA)‐terminated poly (amic acid) precursor resin. 3,3,4,4‐Benzophenone tetracarboxylicdianhydride and 4,4‐diamino diphenylsulfone were used as monomers for the polymer backbones. For the thermosetting composite, NA was also used as an end capper and to provide crosslinking of the polymer chains. On the other hand, the HRACSs had two kinds of core materials with low densities. As core materials, isocyanate‐based PI foams were used. Pyromellitic anhydride and polymeric diphenylmethane diisocyanate were used for the PI foams and the amounts of the additives such as the surfactant, water, and triethylamine. As a result of these variations, different compressive properties and densities were obtained. On the other hand, a polymerization of monomeric reactant (PMR)‐type adhesive PI resin was synthesized in this study. The HRACSs were prepared with the curing and crosslinking of this synthesized PMR‐type adhesive PI resin at the interfaces of the outer face and core materials. These HRACSs exhibited outstanding compressive and flexural properties. The flexural force of the HRACSs increased up to 535 N while the composite laminates exhibited values of 197 and 255 N. Additionally, the thermomechanical properties determined with dynamic mechanical analysis, especially those related to the composite faces, were promising.

Fabrication of polyimide foams with superior mechanical and flame resistance properties utilizing the graft copolymerization between red phosphorus and graphene oxide

In this work, red phosphorus (RP) grafted graphene oxide (GO) was generated inside polyimide foam (PIFs) matrices using a novel method. Definite chemical interaction between RP and GO was confirmed. The RP grafted GO (GO-RP) as a beneficial additive greatly improved the mechanical, thermal and flame resistance properties of the PIFs. Scanning electron microscopy (SEM) revealed the cell size of PIFs/GO-RP minished and homogenized when compared to the pristine PIF. The mean cell diameter decreased to 0.29 mm from 0.38 mm and the open cell content was reduced by 4%. The specific strength increased greatly after adding GO-RP, from 2.14 × 103 N·m/kg to 2.48 × 103 N·m/kg. Besides, the pyrolysis temperature of PIFs/GO-RP shifted to a higher value and the carbon residue increased at 800 °C, indicating excellent thermal properties. The flame resistance property of foams significantly enhanced while the peak heat release rate (PHRR) was reduced by 66% compared to that of the pristine foams. The craft of PIFs/GO-RP presented here has greatly provided an potential value in the design of materials.