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Thermosetting polyimide (PI) foams (PIFs) are usually synthesized through chemical foaming; however, this approach is environmentally toxic, and it is difficult to regulate the cell structure, remold the foam, and increase the foam compressive strength. The development of microcellular PIFs with ultrahigh compressive strength and high volume expansion ratio remains a challenge. Herein, thermoplastic PI with a branched structure and flexible ether bonds was synthesized through solution polymerization, and microcellular thermoplastic PIFs (TPIFs) with ultrahigh strength were fabricated via supercritical-carbon-dioxide foaming using 2,4,6-triamino pyrimidine (TAP) as a chain-extender monomer. Subsequently, a lattice model of a closed tetrakaidecahedral cell was used to clarify the relation between the foam compressive strength and polymer cell structure. Experimental results indicate that the optimal thermal imidization temperature is 230 °C and that the resulting branched structure considerably improves viscoelasticity, flame retardancy, and foaming performance. A TAP content of 0.75 g results in branched-structure TPIFs with a mean cell size of 16.8 μm. Notably, at high temperatures and pressures, the compressive strength of TPIFs with 0.75 g TAP is more than nine times of that of TPIFs without TAP. Increasing the TAP content beyond 0.75 g results in a crosslinked structure. Backward differentiation shows that TPIF compression is constant at 0.14–0.18 in the [0,0,1] lattice direction. The proposed physical foaming method is environment-friendly and can sustainably produce TPIFs with a high volume expansion ratio, an adjustable microcellular structure, and outstanding mechanical properties. [Display omitted] • Branched thermoplastic polyimide (TPI) synthesized via solution polymerization. • TPI offers superb flame resistance and recyclability for fireproofing. • Microcellular TPI foams are fabricated by supercritical CO 2 foaming. • TPI foams exhibit uniform structure and strong compressive strength. • Lattice model clarifiies the relationship between compressive strength and polymer cell structure. [ABSTRACT FROM AUTHOR]

Addressing water pollution issues is directly related to green sustainable development. In this work, a heterostructure polyurethane-based (PU) sponge was prepared by a facile "dip-adhere" strategy to achieve simultaneous and efficient removal of oils and dyes from water. This innovatively designed sponge comprises two functional layers. The hydrophobic/lipophilic octadecylamine-molybdenum disulfide coated PU sponge (ODA-MoS 2 @PU) layer exhibits excellent sorption capacity, ranging from 37.35 to 63.52 times its own weight, for eight organic solvents (DMSO, isopropanol, n-hexane, petroleum ether, n-butanol, glycol, acetone, xylene) and five oils (soybean oil, olive oil, gasoline, diesel, and lubrication). Furthermore, it exhibits robust stability in extreme environments and maintains a high separation efficiency (99 % after 50 separations). The photocatalytic/superhydrophilic polydopamine-molybdenum disulfide coated PU sponge (PDA-MoS 2 @PU) layer demonstrates great photocatalytic degradation efficiency for dyes (96.80 % for methylene blue and 97.39 % for methyl orange). Consequently, the heterostructure PU sponge holds application potential in environment remediation. [Display omitted] • A dual-functional heterostructure sponge was prepared. • Continuous oil-water separation was realized with the oil-gathering device. • The simultaneous treatment of removing oils and dyes was achieved. [ABSTRACT FROM AUTHOR]

Fabrication of polymer films with superb mechanical properties is far from mature compared to that of fibers, hampering the further engineering applications of lightweight polymer materials. Herein, high density polyethylene (HDPE) films reinforced with re-dispersed or refined reduced graphene oxide (rGO) are prepared via a facile melt-stretching strategy. The incorporation of only 0.2 wt% rGO is demonstrated to endow the melt-stretched film (80× stretch ratio) with ultrahigh Young's modulus of 2.9 GPa and tensile strength of 162.2 MPa, which are comparable to many engineering plastics and also significantly superior to the existing HDPE/graphene composites. More importantly, these modulus and strength values are increased by 71 and 65% compared to the neat PE (80×), respectively, far more than the theoretical prediction with the mixing rule. Experimental characterizations indicate that the high-efficient mechanical enhancement is attributed to the strong synergy of melt stretching-driven crystallization and rGO re-dispersion or refinement in constructing the compact and robust shish-kebabs crystal network. Such microstructural characteristics greatly promote the load transfer along the covalently bonded molecular chains, and also from polymer to rigid fillers under loading. Furthermore, the excellent puncture resistance and thermo-mechanical properties of PE/rGO films have been demonstrated. This work provides a feasible way towards scalable manufacturing of high-performance polymer nanocomposite films from general plastics and carbonaceous nanomaterials. [Display omitted] • HDPE/rGO nanocomposite films are fabricated by a facile melt stretching process. • Superb mechanical performance of films is achieved at very low filler content. • Melt stretching-driven rGO re-dispersion or refinement is demonstrated. • rGO re-dispersion enhances the formation of robust shish-kebabs crystal network. • Good puncture resistance and thermo-mechanical properties of films are revealed. [ABSTRACT FROM AUTHOR]

Abstract In this work, linear low-density polyethylene (LLDPE) nanocomposites with different loading levels of multi-walled carbon nanotube (MWCNTs) were prepared by microinjection molding. Interestingly, a similar network structure featured with oriented nanohybrid shish-kebab structure was formed in all the LLDPE/MWCNTs composites. Importantly, the composites with improved strength and modulus in parallel with enhanced toughness were obtained. For example, the tensile strength, modulus and toughness of the composites with 1 wt% MWCNTs were increased by 64.1%, 100% and 134.6%, respectively. This work offers a simple approach to achieve high-performance composites molded by microinjection molding (MIM) together with nanohybrid shish-kebab structure. Graphical abstract Image 1 Highlights • LLDPE/MWCNTs composites were prepared by microinjection molding. • A network structure featured with oriented nanohybrid shish-kebab structure was formed. • Composites with improved strength and modulus in parallel with enhanced toughness were obtained. [ABSTRACT FROM AUTHOR]

Abstract Improving the burning progressivity is an effective approach to improve the muzzle velocities of projectile of a gun. Composite multi-layered flaky gun propellant is a combination of a fast-burning inner layer and a slow-burning outer layer. It has an obvious burning progressivity which decreases the pressure in bore and increases the muzzle velocity, thus this characteristic is widely concerned by the research of gun propellant. The thermal expansion coefficient of composite multi-layered gun propellant has a significant influence on the combustion performance. Therefore, understanding the thermal expansion properties of the composite multi-layered gun propellant is important. In this study, the thermal expansion coefficients were measured by thermal mechanical analyzer (TMA) for a three-layered flaky gun propellant, and the influence of laminating and coating flaky gun propellant on thermal expansion coefficient was investigated. The results showed that the slow-burning layers had a higher thermal expansion coefficient than the faster-burning layers, the thermal expansion coefficient of slow-burning layers was 4–5 times bigger than that of fast-burning layers, and the order of magnitudes was 1 × 10−5 K−1. The laminating and coating had a great influence on the thermal expansion coefficient of flaky gun propellant, the thermal expansion coefficient of laminate sample was 10 times greater than that of the original sample, and the order of magnitudes for two layers and three layers propellant reached 1 × 10−4 K−1. Furthermore, the theoretical relations between the thermal expansion coefficient of axial and the thermal expansion coefficient of the fast and slow burning layer were derived. Graphical abstract Preparation and different test conditions for composite multi-layered flaky gun propellant. Image 1 Highlights • A method to improve the loading density of double-based gun propellant was presented. • A thermal expansion model for the flaky gun propellant was proposed. • The expansion coefficient is only related to the ratio of the fast-burning and slow-burning layers. [ABSTRACT FROM AUTHOR]

Abstract In this work, the rheological and electrical behavior of carbon black (CB) filled poly(methyl methacrylate) (PMMA) nanocomposites in the molten state as a function of CB concentration were investigated by simultaneous electrical and rheological measurements. Shear deformations applied during a stress amplitude sweep caused both changes in the linear viscoelastic behavior and electrical conductivity. The storage modulus increased with measuring time for all PMMA nanocomposites. However, the changes in the time-dependent behavior of storage modulus decreased above the percolated CB concentrations for all investigated nanocomposites, which was in good agreement with the changes in the time-dependent electrical conductivity. The different behaviors can be explained by the agglomeration of CB particles and the decrease of averaged force on a single CB particle. Highlights • Shear deformation applied during stress amplitude sweep caused both changes in the linear viscoelastic and conductivity • Time-dependent behavior of storage modulus was agreed with the conductivity at above the percolated CB content. • Different behaviors were attributed to the CB agglomeration and the decrease of averaged force on a single CB particle. [ABSTRACT FROM AUTHOR]

With the rapid development of new-generation wireless communication technologies and portable intelligent electronic devices, the development of composites with excellent thermal conductivity and electromagnetic shielding properties has become an urgent challenge. In this work, a unique fibers-induced segregated-like structure strategy for fabricating thermoplastic polyurethane/polydopamine/silver (TPU/PDA/Ag) composites film with high thermal conductivity (TC) and excellent electromagnetic interference (EMI) shielding performance is demonstrated via electrospinning-electroless depositing-pressing technology. The TPU/PDA/Ag composites film exhibit excellent in-plane TC of 20.9 W/(m⋅K) at 75 wt% Ag loading, which shows excellent thermal management capability as heat spreaders of high-power light-emitting diode (LED) modules in practice. Meanwhile, the composites film presents outstanding EMI shielding efficiency of 109 dB (8.2–12.4 GHz) with a thickness of 45 μm and prominent EMI shielding reliability after 1000 cycles of bending. In addition, the composites film shows good tensile strength (12.1 MPa), elongation at break (108.0%), and toughness (11.59 MJ/m3). The obtained TPU/PDA/Ag composites film achieves the desired balance among thermal conductivity, EMI shielding, and mechanical properties, indicating broad application prospects in new-generation wireless communication technologies and portable intelligent electronic devices. [ABSTRACT FROM AUTHOR]

In this paper, carbon black (CB), carbon fiber (CF), and hybrid CF/CB were introduced into polypropylene (PP) to fabricate different conductive composites by melt mixing, respectively. The combined effects of CF and CB on the electrical and liquid sensing properties of PP-based composites were investigated in detail. In virtue of the co-supporting conductive network, percolation threshold of the CF/CB/PP composite was reduced apparently upon the addition of 8 wt.% CF. For liquid sensing measurements, CF/CB/PP conductive polymer composites (CPCs) exhibited a superior liquid sensing behavior with higher responsivity, rapider response and better stability in contrast to the counterpart CB/PP. In addition, the response curves are found to be remarkably characteristic for discriminating different kinds of organic solvents. The present paper provides a new route to tailor the liquid sensing properties of CPCs. [ABSTRACT FROM AUTHOR]

Boron nitride/multiwalled carbon nanotubes/carbon (BN/MWCNTs/C) networks were prepared via a rape pollen (RP) biological template assisted strategy. The highly thermally conductive epoxy resin (EP) composites were prepared by impregnating EP into the 3D BN/MWCNTs/C networks. Fourier transform infrared spectra and X-ray photoelectron spectroscopy analyses indicated that the successful modification of BN (m-BN) and the interaction between RP, carboxyl functionalized MWCNTs (c-MWCNTs) and m-BN. Scanning electron microscopy images clearly present the network morphology constructed by MWCNTs connected to m-BN. Thermogravimetric analyzer curves determine the mass concentration of m-BN in EP-based composites. The thermal conductivity (K) reached 1.84 W/(m·K) in the composites at a BN content of 21.3 wt%, displaying a significant enhancement of 868% compared with pure EP. The enhanced K is attributed to the effective connection of BN by the MWCNTs covered on the surface of RP. Meanwhile, the composites exhibit a tensile strength of 39.2 MPa, electrically insulating with a volume electrical resistivity about 9.17 × 1010 Ω cm and good flame retardancy. [Display omitted] • 3D BN/MWCNTs/C thermal conductive networks were prepared via a biological template assisted strategy. • Epoxy-based composites were prepared by a vacuum-assisted impregnation method. • Thermal conductivity was significantly enhanced in this system. • Electrical insulation and flame retardancy performances were observed as well. [ABSTRACT FROM AUTHOR]

The durability and large-scale production of Ti 3 C 2 T x MXene-based composites are the main obstacles in industrialized application. Herein, a scalable blade coating method is demonstrated for fabricating the flexible and durable polyvinylidene fluoride (PVDF)/Ti 3 C 2 T x MXene layered films with compact hierarchical brick-and-mortar structure. The highly aligned MXene nanosheets make the obtained PVDF/MXene films with high electrical conductivity from 21.1 to 214.6 S cm−1. In combination to the multiple wave reflection in hierarchical layered structure and the interfacial polarization between dielectric matrix and MXene, PVDF/MXene films reveal excellent electromagnetic interference (EMI) performance with an optimal specific EMI shielding effectiveness (SSE/t) of 19504.8 dB cm2 g−1 at only 17 μm thickness. More importantly, the PVDF/MXene film can withstand the damages from mechanical deformation, hot/cold attack and chemical corrosion, meanwhile maintain a stable EMI shielding performance within floating of 5%. Besides, arising from the surface plasmon resonance effect and high electrical conductivity, the PVDF/MXene film reveals photo/electro-thermal heating abilities with rapid response time, high stability and controllability, which ensure their reliable EMI shielding performance under extremely cold conditions. [Display omitted] • A scalable blade coating method was reported for fabricating PVDF/MXene layered film. • The film with compact brick-and-mortar structure reveals good EMI shielding property. • PVDF/MXene film shows superior durability with stable EMI SE in various environments. • PVDF/MXene film exhibits multifunctional photo/electro-thermal conversion capacities. [ABSTRACT FROM AUTHOR]

Flexible and wearable strain sensors with multi-functionalities have aroused tremendous attention for various applications in disease diagnostics, environment detection and healthcare monitoring, etc. However, limited electromechanical performance and complicated fabrication process of strain sensors restrict their extensive applications in full-range stimuli monitoring. Herein, we fabricated flexible and wearable strain sensors, consisting of a robust fiber with helical structure and two polyaniline (PANI) layers bridged by reduced graphene oxide (rGO) layer through in-situ polymerization and ultrasonication. The flexible and wearable sensor possesses wide healthcare monitoring range (0.1%–200% strain), high sensibility especially for subtle deformation, excellent response stability, fast response/recovery time (100 ms/100 ms) and favorable durability. Meanwhile, our conductive PANI-rGO-PANI fiber (CPGPF) is assembled as a wearable sensor with the capability of precisely monitoring human body motions, temperature fluctuation and poisonous gas, indicating a promising multifunctional application in human-machine interaction and environment monitoring. [ABSTRACT FROM AUTHOR]

With the rapid development of the flexible electronics industry, the range of multifunctional applications of materials has become extensive. But it is still a challenge to apply flexible materials to different fields while ensuring corresponding performance. Herein, a simple and available approach is addressed to fabricate conductive polymer composite films supported on Ag flakes and waterborne polyurethane (WPU) by spraying. The WPU/Ag films with uniform structure show outstanding flexibility and electromagnetic interference shielding effectiveness of 68.9 dB with thickness of only 50 μm, and could sustain a high standard even undergoing excessive mechanical deformations. Besides, the resulted films possess prominent electro-thermal effect, which can achieve a temperature of over 120 °C by applying a low voltage of 2 V, and the heat can be dissipated rapidly along with the connecting Ag network. Moreover, it shows a high gauge factor (229.2), good durability and reproductivity (over 1000 cycles), and rapid response time to strain (50 ms), which can be potentially used in the field of human movement monitoring and wearable electronic devices. These results indicate the multifunction of the WPU/Ag film, which could widen its practical applications after the corresponding treatment. Image 1 • Multifunctional WPU/Ag composite films were prepared by the solution blending and spraying technique. • The film with a thickness of 50 μm exhibits superior conductivity (1101.32 S cm−1) and EMI SE (68.97 dB). • The film can be rapidly heated to 125 °C under 2.0 V at 1 min. • The film shows high gauge factor (229), goodreproductivity (over 1000 cycles), and rapid response time (50 ms). [ABSTRACT FROM AUTHOR]

The construction of heat conduction paths in the polymer matrix is essential to improve the thermal management performance of polymer composites. A three-dimensional (3D) thermally conductive network with regular filler structures is very attractive for building fast conductive paths in polymer composites. Herein, a unique 3D interconnected tannic acid modified boron nitride (BN) and C network (M-BN/C) was successfully fabricated by the carbonization of M-BN/thermoplastic polyurethane (TPU) skeletons, which were obtained via simple salt template assisted strategy to enhance the thermal transfer properties of composites. The highly thermally conductive epoxy composites (M-BN/C/EP) were then prepared by impregnating epoxy resin (EP) into the 3D M-BN/C network. The thermal conductivity of the composites with a M − BN loading of 23 wt% is as high as 1.524 W/(m·K), which exhibits a significant enhancement of 702% compared with pure EP. In addition, our composite exhibited outstanding thermal behaviors during heating and cooling processes. Furthermore, the finite element heat conduction simulation further analyzes the heat conduction mechanism of epoxy composites from the theoretical level. This work provides a new idea to significantly enhance the thermal conductivity of thermal management materials. [ABSTRACT FROM AUTHOR]

Various sensors have been developed to monitor the changes in physical quantities to meet the growing demand for wearable electronics. While it is still a huge challenge to design a multifunctional flexible sensor with both high strain responsivity and good breathability. In this work, through electrospinning, ultrasonication and in-situ polymerization of dopamine, we prepared a multifunctional strain sensor. We decorated polydopamine (PDA) onto the surface of reduced graphene oxide (RGO)/thermoplastic polyurethane (TPU) fibers. Here, PDA containing hydrophilic groups (-OH, –NH 2) was used to improve the hydrophilic breathability of the membrane and prevent the RGO falling off from TPU fibrous mat. The PDA/RGO/TPU (PRT) fibrous strain sensor exhibits excellent comprehensive performance of excellent stretchability, good durability (stretching/releasing test of 9000 cycles under 50% strain), high sensitivity (gauge factor (GF) 23.2 within 60% strain, 185 towards 60%–100% strain), and fast response time (100 m s). Specially, owing to the introduction of PDA, the water vapor volatilization rate of our PRT strain sensor (38%) is almost the same as the blank control group (39%), indicating that our fibrous sensor has excellent breathability. In order to monitor various movements of human body parts (finger, wrist, elbow, and leg bending), our sensors were attached to volunteers' joints to monitor resistance changes in real time. In addition, our PRT fibrous mat also has excellent sensitive performances towards organic gases and humidity, showing its multifunctional ability for detecting various environment stimuli. Image 1 [ABSTRACT FROM AUTHOR]