Flexible Composites Research Articles

Effect of Bi2O3 nanostructures on X-ray shielding, thermal, mechanical and biological properties of PVC polymer nanocomposites

The effect of Bi2O3 nanoparticles and nanowires as fillers in flexible PVC composites was investigated on the shielding properties against X-ray radiation at radiodiagnostic energies (50–129 kV). The PVC composites were gamma radiation cross-linked at 75 kGy. Materials were characterized by thermal analyses, and microstructure studied by SEM. The evaluation involved attenuation measurements and toxicity through cell viability assay. The mechanical properties and toughness were highly improved, according to DMA results, and the TGA analysis shows a small influence of the Bi2O3 nanostructures in the dehydrochlorination reaction of PVC during its thermal decomposition. Moreover, SEM images show a uniform distribution of the Bi2O3 nanostructures in the PVC matrix. Attenuation measurements showed low levels of X-ray transmission for PVC composites with 50 %wt of Bi2O3 and a mass attenuation coefficient greater than those reported for lead in the energy ranges studied, which is an improvement with the use of Bi2O3 NWs. In addition, PVC composites show low HVL and TVL values, making them feasible for the attenuation property. Density measurements show that the composites are lighter than lead. No-toxicity was observed for these composites through cell viability assay. Therefore, the investigated PVC composites are suitable for preparing new radiation-attenuating materials using Bi2O3 NWs.

Low-cost, simple preparation and outstanding energy density of glass fiber reinforced PVDF polymer flexible composites

To make the product commercially viable and applicable, the inclusion of glass fiber filler with a low cost and medium dielectric constant (ε) is adopted as the filler. Synchronously, representative polyvinylidene fluoride (PVDF) with high permittivity and breakdown strength is selected as optimal polymer matrix. And surface modifying agent is employed as organic coatings to weaken the surface energy of glass fiber and boost the interfacial inter-action. An investigation of dielectric properties was conducted by preparing flexible composites consisting of various content of glass fiber. The ε of composites can be significantly enhanced in the PVDF composites with glass fiber, and the breakdown strength (BDS) is remained at a high level. Moreover, within a specific content range, glass fiber makes the ε and BDS of the material increase synchronously. This work provides a facile strategy for the development of excellent performance, simple preparation and low-cost flexible composites.

Preparation and properties of flexible electromagnetic shielding composites

Preparation and properties of flexible electromagnetic shielding composites

Study on tensile strain of carbon fiber triaxial woven fabric/thermoplastic polyurethane flexible textile composites

AbstractIn order to study the possibility of flexible textile composites as space deployable devices, carbon fiber triaxial woven fabric and thermoplastic polyurethane were compounded by hot‐pressing. The section shape of the carbon fiber triaxial woven fabric flexible textile composites was observed by scanning electron microscopy. After hot‐pressing at 120°C for 45 min, the thermoplastic polyurethane is best combined with carbon fiber bundle, and fully melted to form a protective layer, which also ensured the deformability of carbon fiber triaxial woven fabric/thermoplastic polyurethane flexible textile composites. The tensile strains of flexible textile composites in the directions of 0°, 15° and 30° were analyzed by digital image correlation. The analysis was carried out from the macroscopic scale, the single cell scale, and the fiber bundle scale, combined with the strain distribution of digital image correlation in the tensile process. From the axial and radial deformation of the bundle and the force analysis of single cell, the phenomena such as strain change, trellising phenomenon, and fabric deformation during tensile were explained. When carbon fiber triaxial woven fabric is added to glass‐fiber composite, the electromagnetic reflection efficiency can be increased by 9%. The research on strain and electromagnetic reflection provided the possibility for the flexible textile composites as a space deployment device.Highlights Through the use of SEM and hot‐pressing, carbon fiber triaxial woven fabric/TPU flexible textile composites with high coverage were produced. The differences in strain distribution and deformation process throughout the CTFC tensile process at 0°, 15°, and 30° are investigated by DIC and stress analysis. Carbon fiber triaxial woven fabric (TWF) can reflect electromagnetic radiation. TWF can increase the efficacy of reflection in composites. Space deployment is a possible application of TWF.

Tensile properties of flexible composites with knitted reinforcements from various yarn materials

AbstractThe tensile behavior of a flexible epoxy resin reinforced with knitted reinforcements from various fiber materials was comprehensively studied in the wale and course direction. By measuring dry yarns, temperature‐treated yarns, dry knitted fabrics and flexible composites, the effect of the fiber material and the knitted fabric on the tensile properties was analyzed. The interlock knit structure strongly affected the deformation behavior of the flexible composites which differed significantly from the dry knitted fabrics. The deformation behavior of the flexible composites was monitored using digital image correlation which revealed the formation of cracks and high local strain differences in the course direction for all fiber materials. This was linked to fiber‐matrix debonding by scanning electron microscope observations. In the wale direction, the deformation of the knitted structure under tensile load led to plastic deformation of the matrix material. Overall, with yarns from recycled thermoplastic fibers, a higher maximum stress and strain at break was achieved compared to bio‐based fibers. However, irreversible damage occurred for all fiber materials at similar strain values.Highlights Tensile tests on yarns, knitted fabrics and flexible composites. Investigation of the effect of fiber material on mechanical properties. High local strain differences in composites due to knitted structure. Fiber‐matrix debonding in course direction. Plastic deformation of the matrix material in the wale direction.

Tailoring the Electrical Response of Polyvinylidene Fluoride Nanocomposites with Electrically Conductive and Dielectric Fillers

Polymer‐based composites combining the flexibility, low density, and processability of the matrix with the tailored functional performance provided by the fillers are also particularly suitable for large area, flexible, and printable applications. Herein, polyvinylidene fluoride (PVDF) composites with conductive graphene nanoplatelets (G‐NPL) and high‐dielectric constant ceramics, including barium and strontium titanate (BT and SrT), have been developed to achieve electrically conductive and high‐dielectric response materials, respectively. Flexible composites reinforced with 45 wt% ceramic content lead to a dielectric constant of ε´ = 33 and 25 for BT and SrT, respectively, 6 and 4 times higher than for pristine PVDF. Further, the inclusion of G‐NPL allows for the development of highly conductive composites with a maximum conductivity of 5.5 × 10−2 (Ω.m)−1 for a 5 wt% filler content, 10 orders of magnitude larger than PVDF. The G‐NPL and ceramic in optimized contents in PVDF tricomposites do not enhance the dielectric properties compared to PVDF‐ceramic composites. Theoretical analysis has been used to determine the critical percolation threshold of the PVDF/G‐NPL, which occurs at 0.6 wt% G‐NPL content with a critical exponent of t = 2.49 and to describe the dielectric properties of the composites, allowing to further tailor materials responses for specific application needs.

Localized fabrication of flexible graphene-copper composites via a combined ultrafast laser irradiation and electrodeposition technique

Graphene-metal composites (GMC) possess superior properties, such as high specific strength, and high thermal and electrical conductivity, and have been widely used in many fields. However, the fabrication of GMC still remains to be explored, as existing methods via powder metallurgy and chemical synthesis are difficult to achieve uniform dispersion of graphene, not to mention achieving selective and localized preparation of GMC with complex patterns. In this paper, a simple method for the fabrication of graphene-copper composites (GCC) is firstly proposed by combining flexible laser irradiation and efficient electrodeposition. It not only effectively solves the problems of graphene agglomeration and inhomogeneous dispersion in GCC, but also enables the selective and precise preparation of GCC with spatial micro-patterns. Specifically, an ultrafast picosecond (ps) laser is firstly used to irradiate the polyimide (PI) film to selectively and precisely produce the desired laser-induced graphene (LIG) region. The localized deposition of copper atoms is subsequently made via the electrodeposition step, forming the flexible GCC with a laser-determined spatial pattern. The experimental study of LIG process on PI film has been carried out, and high-quality LIG region is obtained by optimizing the laser scanning path and parameters. On this basis, the regional flexible GCC of 45 μm in thickness with a compact and uniform copper layer of 20 μm has been efficiently fabricated, followed by the detailed characterizations of surface morphology and chemical composition. Furthermore, a significant enhancement of the electrical conductivity has been confirmed, as the measured value is up to 32.8 S/cm at the LIG region and further to about 60.9 S/cm at the GCC area. The mechanical properties of the obtained conductive GCC have been tested and good flexibility is confirmed by nanoindentation and bending tests, verifying its potential for a wide range of applications in flexible electronics, medical and many other fields.

All-in-one integrated flexible PE@PET/MXene films for high-performance electromagnetic shields with self-reinforced conductivity and mechanical properties

MXene-based composites are deemed as promising electromagnetic interference (EMI) shielding candidates to address the rapidly increasing electromagnetic interference and radiation concerns. However, developing high-performance flexible polymer-MXene composites with excellent EMI shielding efficiency (EMI SE), good mechanical properties and superior serving stability is a significant challenge. Herein, a type of all-in-one designed lightweight, thin, ultra-flexible PE@PET/MXene films are developed using a novel PE@PET nonwoven fabric (NWF) as the supporter. A mussel-inspired polydopamine modification facilitates the uniform loading of MXene, achieving high electrical conductivity of the resultant PE@PET/MXene films. A simple hot-pressing process is then employed to melt the sheath PE component of PE@PET to serve as a “self-glue” in adhering and wrapping the loaded MXene nanosheets, while maintaining the core PET fibers as the internal “steel” skeleton. As such, the resultant PE@PET/MXene films exhibit multiple self-enhancement metrics involving high mechanical strength, good electrical conductivity, robust serving stability, and superior EMI shielding performance. An optimized PE@PET/MXene film can preserve an excellent EMI SE of 50.44 dB and an ultra-high absolute shielding effectiveness (SSE/t) of 10606 dB cm2 g−1. The versatility of PE@PET/MXene EMI shielding films is further indicated by integrating the flame-retardant additives to endow its flame-retardant function, demonstrating excellent versability and expandability.

Research progress of filled-type high-thermal-conductivity flexible polyimide composites: a review

Research progress of filled-type high-thermal-conductivity flexible polyimide composites: a review

Anisotropic Piezoresistive Sensors Made with Magnetically Induced Vertically Aligned Carbon Nanotubes/Polydimethylsiloxane.

A piezoresistive material consisting of internal vertically aligned carbon nanotubes acting in concert with an external microdome structure is prepared to obtain a flexible piezoresistive sensor with high anisotropy. Here, we first obtained flexible piezoresistive composites (VCP) with anisotropic properties by inducing the vertical alignment of multiwalled carbon nanotubes in the pressure direction under a weak magnetic field of 0.6 T. Then, the composite with a microdome structure on the surface (m-VCP) was fabricated by a mold with a microstructure to further increase the anisotropy of the composite. The m-VCP microstructure was docked with VCP and placed between two layers of copper foil. With the synergistic effect of vertically aligned carbon nanotubes and the microdome structure, the sensitivity of the flexible sensor in the pressure direction was dramatically increased. In the low-strain range (0-6%), the sensitivity of m-VCP (GF = 9.208) is improved by 49% compared to m-CP and by 86% compared to VCP. The sensor has high anisotropy in the piezoresistive direction and retains good fatigue resistance under fatigue testing for 2000 cycles. This means that the sensor can be used in emerging fields such as human health monitoring, wearable electronics, and intelligent human-computer interaction.

Fabrication of shape memory polyimides with exploration of their activation mechanisms

The construction of polymer-based materials with reversible bidirectional shape memory effects, good thermal and electrically controlled properties is of paramount importance for the development of intelligent exploration in high-temperature fields. By adjusting the hydrogen bond contents of the structure to regulate the intermolecular strength, a series of random shape memory copolyimides have been synthesized with the triggering temperatures ranging from 275 to 384℃, which displayed good thermal stability, high shape fixation rate and shape recovery rate of over 95 % and 98 %, respectively, and excellent shape recovery speed (∼9 s). Visualized quantification of the microstructural phase evolution during stretching and the effects of hydrogen bonds on the properties of polyimide were deeply explored to better understanding the activation mechanisms of shape memory behaviors. Furthermore, flexible fabric composites with bidirectional shape memory effects motivated by electrical signals were also designed, providing a new sight of exploration for high-temperature shape-memory materials.

Flexible Composites for Piezocatalysis.

Despite piezoelectric materials have a long history of application, piezoelectric catalysis has continued to be a hot topic in recent years. Flexible piezoelectric materials have just emerged in recent years due to their versatility and designability. In this paper, we review the recent advances in flexible piezoelectric materials for catalysis, discuss the fundamentals of the catalytic properties of composite materials, and detail the typical structures of these materials. We pay special attention to the types of filler in flexible piezoelectric composites, their role and the interaction between the particles and the flexible substrate. Notable examples of flexible piezoelectric materials for organic pollutants degradation, enhanced piezo-photocatalysis and antibacterial applications are also presented. Finally, we present key issues and future prospects for the development of flexible piezoelectric catalysts.

Bio-inspired smart composite architecture for thermally tunable green EMI shielding

Bio-imitating externally stimulated smart flexible composites are highly sought after for the innovations of next-generation advanced artificial intelligence-based electronic technologies, such as robots, defense, wireless and satellite communications, etc., to protect from electromagnetic interference (EMI). Herein, eco-friendly active guest in passive host composite of polydimethylsiloxane (PDMS)/silver-doped zinc stannate (SZTO)/single wall carbon nanotubes (SWCNT) containing an active fluid (water) was fabricated for thermally tuned smart EMI shielding. This soft robust composite with ultra-low fillers integrates temperature induced outstanding smart EMI shielding capabilities in the 14.5 GHz to 20 GHz frequency band. The water serves as a temperature responsive active phase, enhancing the radiation-shielding performance up to 50.4 dB at 100 °C. Additionally, the composite exhibits a green index greater than six, indicating an extraordinary absorption-dominated green shielding response. Hence, this design strategy enables the development of externally stimulated multifunctional autonomous composite architecture for smart green EMI shielding.

Unleashing the potential of morphotropic phase boundary based hybrid triboelectric–piezoelectric nanogenerator

Morphotropic phase boundary (MPB)-based ceramics are excellent for energy harvesting due to their enhanced physical properties at phase boundaries, broad operating temperature range, and ability to customize properties for efficient conversion of mechanical energy into electrical energy. In this work, Bi1–xNaxFe1–xNbxO3 (x = 0.20, 0.30, 0.32 and 0.40, BNFNO abbreviation) based ceramics were synthesized using a solid-state route and blended with Polydimethylsiloxane (PDMS) to achieve flexible composites. Various material characterization and energy harvesting were performed by designing a hybrid piezoelectric (PENG)-triboelectric (TENG) device. The voltage and current of PENG, TENG, and hybrid bearing same device area (2 cm × 2 cm) were recorded as 11 V/0.3 μA; 60 V/0.7 μA; 110 V/2.2 μA. The strategies for enhancing the output performance of the hybrid device were evaluated, such as increased surface area (creating micro-roughness and porous morphology) and increasing electrode size and multi-layer hybrid device formation. The self-powered acceleration monitoring was demonstrated using the hybrid device. Further, the low-frequency-based wave energy is converted into electrical energy, confirming the usage of hybrid PENG-TENG devices as a base for battery-free sensors and blue energy harvesting.

Development and ballistic impact study on environment friendly sustainable jute reinforced carbon black/lignin-based elastomeric flexible composites

This study compares the behaviour of jute/elastomer bio-composites based on lignin and carbon black under high-velocity impact using experimental methods. Compared to carbon black, SEM data showed that lignin was more evenly distributed across the yarns. The space between the threads was filled by the good interaction of lignin and rubber. Additionally, the findings of the tensile and dynamic compression tests demonstrate that adding lignin to a matrix enhances the tensile strength of rubber samples and composites. On single-layer and three-layer composites made of lignin and carbon black, experimental tests were conducted utilizing a gas gun apparatus with a flat projectile travelling between 100 and 180 m/s. The damage behaviour of the proposed composites is analyzed. The findings demonstrate that the composites' energy absorption and ballistic velocity have enhanced due to the jute-woven fabric cover and the diluted rubber matrix. The results reveal that single and three-layer lignin-based composites exhibit better ballistic limits with an increase of 12.5% and 23.8% over composites based on single and three-layer carbon black composites. Lignin-based composites outperform carbon black composites in terms of energy absorption with single and three-layered lignin-based composites absorbing 23.5% and 25.86% more energy compared to single and three-layered carbon black-based composites. Additionally, the analysis of energy absorption at the ballistic limit for single-layer and three-layer lignin-based composites reveals an increase of 26.56% and 53.35%, respectively, compared to carbon black-based composites.

Carbon fiber in situ grown ZIF‐67 nanocrystals with excellent electrochemical and interfacial property

AbstractCarbon fiber(CF) reinforced flexible composites had a wide range of applications. However, the interfacial adhesion of composites was weak as a result of the smooth and chemically inert CF surface. To settle this issue, this paper described a method to enhance the specific surface area, roughness and wettability of the CF surface by in situ growing Cobalt‐based zeolitic imidazolate framework (ZIF‐67) nanocrystals and CF reinforced waterborne polyurethane (WPU) composites were prepared by a simple casting method. Scanning electron microscopy clearly revealed uniformly grown ZIF‐67 nanoarrays with distinct morphology on the CF surface. As a result, the CF@ZIF‐3 electrode exhibited excellent electrochemical property, with specific capacitance reaching 368.2 mF/cm2. The reinforcing effect of ZIF‐67 with different morphology was further verified through transverse fiber bundle tension test and shear bonding strength measurements, showing improvements of 51.9 and 72.1% respectively, in comparison to the CF/WPU composites due to the unique structure of the ZIF‐67 nanocrystals acted as buffer area, effectively relieving stress concentration and altering the direction of crack propagation. As a result, the interfacial properties of the composites were enhanced. Moreover, tensile and tear strengths of CF@ZIF/WPU composites showed remarkable improvement compared to CF/WPU composites. This study presented a potential reinforcement strategy for achieving high‐performance CF/WPU composites.Highlights ZIF‐67 with different morphologies were grown in situ on the CF surface. CF@ZIF electrode exhibited excellent electrochemical property. ZIF‐67 interface layer improved interfacial properties of composites. The tensile strength of the composites improved after ZIF‐67 modification. Introduction of ZIF‐67 enhanced the tear strength of composites.

White light-emitting calcium tungstate microspheres synthesized via co-precipitation at room temperature and application to UV-LED chip

Crystalline CaWO4 was synthesized by a co-precipitation method at room temperature. XRD peak at a position like that in the reference pattern, and the signal was detected from the (112) plane. Raman signals suggested the presence of symmetrical vibrations of the WO4 bond. The absorption was observed in the UV region, and the bandgap calculated from the Tauc plot was 4.47 eV. When the sample was excited at 230 nm, blue emission with a peak at 430 nm was observed. Crystalline CaWO4 was doped with Dy3+ ions to synthesize a white light-emitting phosphor. The addition of Dy3+ ions altered the crystal structure and shifted the Raman signals slightly. The sample was excited at 230 nm, both 430 nm and 575 nm emissions were observed, and the intensity of the 575 nm emission increased with increasing Dy3+ concentration. The CaWO4:0.1Dy3+ sample showed the highest luminescence intensity, and excessive doping decreased the luminescence intensity owing to concentration quenching. The photoluminescence decay lifetime initially increased with increasing Dy3+ concentration but decreased at concentrations greater than 0.1 mol% because of concentration quenching. The synthesized white light emitting CaWO4:Dy3+ powder was mixed with PDMS to form a flexible composite. The composite could be easily bent with a finger and emitted white light when applied on a UV-LED chip.

From synthesis to fabrication: Engineering thin translucent films with green persistent luminescent nanoparticles

Green-emitting ZnGa2O4:Mn2+ persistent luminescent nanoparticles were synthesized via a solvothermal method followed by a microwave-assisted sintering at 1150 °C. The obtained cubic-like particles averaged 62 ± 16 nm by Transmission Electron Microscopy (TEM) and presented afterglow for up to 2 h after a 5 min excitation in the UV. By Electron Paramagnetic Resonance (EPR), it was observed that the Mn2+ dopant replaces uniquely Zn2+ sites during synthesis. The obtained particles were dispersed with hydroxypropyl methylcellulose (HPMC) in water to create thin films by drop-casting. The films with different concentrations of nanoparticles (1 g/m2, 10 g/m2 and 100 g/m2) had average visible transmittances between 20% and 24%, and presented persistent luminescence after UV excitation, with longer duration by increasing nanoparticle concentration. By synchrotron X-ray Fluorescence (XRF) nanomapping of these films it is possible to see clusters of up to 6 μm of the nanoparticles in the film due to water pockets during film-casting. The X-ray Excited Optical Luminescence (XEOL) showed only Mn2+ emission and the XEOL-XRF mapping proved the integrity of the nanoparticles after film fabrication. By combining the solvothermal method, microwave-assisted sintering, and drop casting, this study establishes a promising pathway for the development of advanced flexible and translucent persistent luminescent composites.

Computation-guided design of flexible piezoelectric composites by optimizing charge-stress transmission

Flexible piezoelectric materials have attracted increasing attention as active components in wearable and flexible electronics, soft robotics and artificial skins or muscles. Although constructing polymer-based composites is becoming a common solution to balance their piezoelectricity and flexibility, challenges associated with the electrical and mechanical mismatch between the polymer matrix and the ceramic fillers remain. Here, taking the piezoelectric composite of lead zirconate titanate-polydimethylsiloxane (PZT/PDMS) as the example, we perform phase-field simulations to spatially and temporally study the electrical and mechanical response. It is found that good connectivity of fillers could provide a load transfer path and break topological restriction of filler morphology on polarization dipoles. Then, we propose an interface design strategy to address the mismatch problem in ‘3–3’ composites, which could greatly enhance the overall piezoelectric response under different modes of compressing, stretching and bending. Finally, we experimentally fabricate high-performance flexible composites with an ultrahigh piezoelectric charge coefficient of 155 pC N−1 and a low Young’s modulus of 63 MPa. This research offers a promising route for designing flexible piezoelectric composites by synergistically regulating connectivity and mismatch problems, which is also expected to guide the optimization of other actuators or sensors related with electromechanical coupling effect.

A novel flexible biocomposite with hemp woven fabric and natural rubber based on lignin green filler: investigation numerical and experimental under high-velocity impact

In this study, the comparison of the behavior of hemp/elastomeric biocomposites based on lignin and carbon black has been investigated experimentally and numerically under the influence of high speed. SEM images confirmed the dispersion and good interaction of lignin in natural rubber with a uniform surface coverage of fibers and the gap of yarns. The results of tensile and dynamic compression tests showed that elastomer with lignin filler improves tensile strength for rubber samples and composites compared to carbon black. The high-velocity impact tests were performed on single-layer and three-layer composites based on lignin and carbon. The penetration resistance and failure mechanism of the composites during impact were validated using a constitutive material model for hemp fabric and a user-defined material model (VUMAT) for the nonlinear behavior of rubber materials with a damage criterion in ABAQUS/Explicit. For one-layer and three-layer flexible composites based on lignin, the ballistic limit is 49 and 96 m s−1, respectively. Compared to carbon-based composites, it has increased by 11.36 and 13% for one-layer and three-layers, respectively. Using the dilute matrix to cover hemp fabric increases the resistance of this type of fabric against high-speed impact. Through tensile failure, the stress is transferred to the surrounding fiber bundles so that more threads can participate in the load-bearing process. As a result, the penetration depth in lignin-based composites is lower, and the protective margin is greater, which increases energy absorption.