Search Results (18)

The intrinsic trade-off among sensitivity, response speed, and measurement range continues to hinder the wider adoption of flexible pressure sensors in areas such as medical diagnostics and gesture recognition. In this work, we propose a grid-structured polycaprolactone/thermoplastic-polyurethane nanofiber pressure sensor decorated with multi-walled carbon nanotubes (PCL/TPU@MWCNTs). By introducing a gradient grid membrane, the strain distribution and reconstruction of the conductive network can be modulated, thereby alleviating the conflict between sensitivity, response speed, and operating range. First, static mechanical simulations were performed to compare the mechanical responses of planar and grid membranes, confirming that the grid architecture offers superior sensitivity. Next, PCL/TPU@MWCNT nanofiber membranes were fabricated via coaxial electrospinning followed by vacuum-filtration and assembled into three-layer planar and grid piezoresistive pressure sensors. Their sensing characteristics were evaluated by simple index-finger motions and slide the mouse wheel identified. Within 0–34 kPa, the sensitivities of the planar and grid sensors reached 1.80 kPa⁻¹ and 2.24 kPa⁻¹, respectively; in the 35–75 kPa range, they were 1.03 kPa⁻¹ and 1.27 kPa⁻¹. The rise/decay times of the output signals were 10.53 ms/11.20 ms for the planar sensor and 9.17 ms/9.65 ms for the grid sensor. Both sensors successfully distinguished active index-finger bending at 0–0.5 Hz. The dynamic range of the grid sensor during the extension motion of the index finger is 105 dB and, during the scrolling mouse motion, is 55 dB, affording higher measurement stability and a broader operating window, fully meeting the requirements for high-precision hand-motion recognition. Full article

Flexible strain sensors have attracted significant attention due to their critical applications in wearable devices, biological detection, and artificial intelligence. However, achieving both a wide strain range and high sensitivity remains a major challenge in current research. This study aims to develop a novel composite material with a synergistic conductive network to construct high-performance flexible strain sensors. Thermoplastic polyurethane (TPU) nanofiber membranes were first prepared using electrospinning technology, and their surface was modified with polydopamine (PDA) via in-situ polymerization, which significantly enhanced the fibers’ adsorption capacity for conductive materials. Subsequently, carbon nanotubes (CNTs) and carbon black (CB) were coated onto the PDA-modified TPU fibers through ultrasonic anchoring, forming a CB/CNT/PDA/TPU composite with a synergistic conductive network. The results demonstrated that the flexible strain sensor fabricated from this composite material (with a CB-to-CNT mass ratio of 7:3) achieved ultrahigh sensitivity (gauge factor, GF, up to 1063) over a wide strain range (up to 300%), along with a low detection limit (1% strain), fast response and recovery times (137 ms), and exceptional stability and durability. Further evaluations confirmed that this sensor reliably captured biological signals from various joint movements, highlighting its broad application potential in human motion monitoring, human–machine interaction, and soft robotics. Full article

This study investigates the influence of thermoplastic polyurethane (TPU) reinforced with jute cellulose nanofibers (CNFs) on the water absorption and mechanical properties of geopolymer concrete. The integration of TPU/jute CNF nanocomposites into geopolymer concrete is explored as a strategy to enhance both its durability and mechanical performance. Geopolymer concrete, a sustainable alternative to traditional Portland cement concrete, is known for its low carbon footprint, but it suffers from high brittleness and water absorption. The water absorption behavior of the modified concrete was assessed, revealing a significant reduction in water uptake due to the hydrophobic nature of TPU and the reinforcing effect of jute CNFs. Additionally, the mechanical properties, including compressive and flexural strengths, were evaluated to understand the impact of the nanocomposites on the structural integrity of the concrete. The addition of TPU/jute CNFs notably enhanced the splitting tensile strength (63.5%), compressive strength (59%), and water absorption (0.59%) of the composite, indicating a promising route for developing high-performance construction materials. The integration of 6 wt% of TPU/jute CNF nanocomposites was found to be optimal, resulting in a uniform matrix, reduced micro-cracks, and improved compressive strength due to enhanced adhesion between the nanocomposites and the geopolymer matrix. Furthermore, a curing temperature of 100 °C was identified as ideal, minimizing unreacted fly ash and enhancing adhesion strength, while higher temperatures (140 °C) led to material deterioration due to rapid water loss. The findings demonstrate that the addition of TPU/jute CNF nanocomposites not only improves resistance to water penetration but also enhances overall mechanical performance. This supports the development of more sustainable and resilient construction materials, contributing to global efforts to reduce the environmental impact of the construction industry. Future research should focus on the long-term durability of these composites under various environmental conditions to validate their effectiveness in real-world applications. Full article

With the rapid advancement of the flexible electronics industry, there is an urgent need to enhance the mechanical properties and thermal stability of flexible electronic devices to expand their range of applications. To address this need, flexible conductive composites have been developed using waterborne polyurethane (WPU) as the matrix, carbon nanotubes (CNTs) and graphene (GA) as conductive fillers, and incorporating cellulose nanofibers (CNFs). The carbon fillers create a conductive and thermal conductivity network within the matrix, while the presence of CNFs improves the dispersion of CNTs and GA, thereby enhancing the overall network structure. The resulting WGNF composites exhibit a resistivity of up to 1.05 × 10⁴ Ω·cm, a tensile strength of 26.74 MPa, and a thermal conductivity of 0.494 W/(m·K). This demonstrates that incorporating cellulose offers an effective solution for producing high-performance polymeric conductive and thermally conductive composites, showing promising potential for flexible wearable devices. Full article

Nanomaterials are known as the most promising materials of the 21st century, among which nanofibers have become a hot research and development topic in academia and industry due to their high aspect ratio, high specific surface area, high molecular orientation, high crystallinity, excellent mechanical properties, and many other advantages. Electrospinning is the most important preparation method for nanofibers and their thin membranes due to its controllability, versatility, low cost, and simplicity. Adding nanofillers such as ceramics, metals, and carbon materials to the electrospinning polymer solutions to prepare composites can further improve the mechanical strength and multi-functionality of nanofibers and their thin membranes and also provide possibilities for their widespread applications. Based on the rapid development in the field of polymer composite nanofibers, this review focuses on polyurethane (PU)-based composite nanofibers as the main representative and reviews their latest practical applications in many fields such as sound-absorbing materials, biomedical materials (including tissue engineering implants, drug delivery systems, wound dressings and other anti-bacterial materials, health materials, etc.), wearable sensing devices and energy harvesters, adsorbent materials, electromagnetic shielding materials, and reinforcement materials. Finally, a summary of their performance–application relationship and prospects for further development are given. This review is expected to provide some practical experience and theoretical guidance for further developments in related fields. Full article

Flexible conductive films are a key component of strain sensors, and their performance directly affects the overall quality of the sensor. However, existing flexible conductive films struggle to maintain high conductivity while simultaneously ensuring excellent flexibility, hydrophobicity, and corrosion resistance, thereby limiting their use in harsh environments. In this paper, a novel method is proposed to fabricate flexible conductive films via centrifugal spinning to generate thermoplastic polyurethane (TPU) nanofiber substrates by employing carbon nanotubes (CNTs) and carbon nanofibers (CNFs) as conductive fillers. These fillers are anchored to the nanofibers through ultrasonic dispersion and impregnation techniques and subsequently modified with polydimethylsiloxane (PDMS). This study focuses on the effect of different ratios of CNTs to CNFs on the film properties. Research demonstrated that at a 1:1 ratio of CNTs to CNFs, with TPU at a 20% concentration and PDMS solution at 2 wt%, the conductive films crafted from these blended fillers exhibited outstanding performance, characterized by electrical conductivity (31.4 S/m), elongation at break (217.5%), and tensile cycling stability (800 cycles at 20% strain). Furthermore, the nanofiber-based conductive films were tested by attaching them to various human body parts. The tests demonstrated that these films effectively respond to motion changes at the wrist, elbow joints, and chest cavity, underscoring their potential as core components in strain sensors. Full article

In this study, nanofibers obtained through the electrospinning process are explored for strain-sensing applications. Thermoplastic polyurethane (TPU) flexible structures were fabricated using the solution electrospinning process (SEP) technique. Subsequently, these structures were nanomodified with single-walled carbon nanotubes (SWCNTs) through immersion into an ultrasonicated suspension containing 0.3 wt% SWCNTs. The nanomodification aimed to impart an electrically conductive network to the structures. Micro-tensile tests and electrical resistance measurements were conducted to characterize the apparent mechanical and electrical properties, respectively. The fabricated structures demonstrated potential as wearable strain sensors for monitoring changes in strain across various applications. The samples exhibited excellent performance, high sensitivity, outstanding mechanical properties, and a broad stretching range. Scanning electron microscopy (SEM) observations provided qualitative insights into the activated conductive pathways during operation. Full article

A triboelectric nanogenerator (TENG) is one of the most significantly innovative microdevices for built-in energy harvesting with wearable and portable electronics. In this study, the forcespinning technology was used to synthesize a nanofiber (NF) mat-based TENG. Polyvinylidene fluoride (PVDF) membrane was used as the negative triboelectric electrode/pole, and chemically designed and functionalized thermoplastic polyurethane (TPU) was used as the positive electrode/pole for the TENG. The electronic interference, sensitivity, and gate voltage of the synthesized microdevices were investigated using chemically modified bridging of multi-walled carbon nanotubes (MWCNT) with a TPU polymer repeating unit and bare TPU-based positive electrodes. The chemical functionality of TPU NF was integrated during the NF preparation step. The morphological features and the chemical structure of the nanofibers were characterized using a field emission scanning electron microscope and Fourier-transform infrared spectroscopy. The electrical output of the fabricated MWCNT-TPU/PVDF TENG yielded a maximum of 212 V in open circuit and 70 µA in short circuit at 240 beats per minute, which proved to be 79% and 15% higher than the TPU/PDVF triboelectric nanogenerator with an electronic contact area of 3.8 × 3.8 cm², which indicates that MWCNT enhanced the electron transportation facility, which results in significantly enhanced performance of the TENG. This device was further tested for its charging capacity and sensory performance by taking data from different body parts, e.g., the chest, arms, feet, hands, etc. These results show an impending prospect and versatility of the chemically functionalized materials for next-generation applications in sensing and everyday energy harvesting technology. Full article

Composites of polyurethane and graphite and polyurethane and carbon nanofibers (PU/Graphite 0.5% and PU/CNF 1%) were synthesized and used as anodes in dual-compartment microbial fuel cells (MFCs) for municipal wastewater treatment; electrical energy generation and organic matter removal were assessed. The maximum power density, coulombic efficiency and chemical oxygen demand (COD) removal efficiency in the MFCs packed with the PU/Graphite 0.5% and PU/CNF 1% composites were 232.32 mW/m³ and 90.78 mW/m³, 5.87 and 4.41%, and 51.38 and 68.62%, respectively. In addition, the internal resistance of the MFCs with the best bioelectrochemical performance (PU/Graphite 0.5%) was 1051.11 Ω. The results obtained in this study demonstrate the feasibility of using these types of materials in dual-compartment MFCs for wastewater treatment with electric power generation. Full article

Thermoplastic polyurethane (TPU) has been widely used as the elastic polymer substrate to be combined with conductive nanomaterials to develop stretchable strain sensors for a variety of applications such as health monitoring, smart robotics, and e-skins. However, little research has been reported on the effects of deposition methods and the form of TPU on their sensing performance. This study intends to design and fabricate a durable, stretchable sensor based on composites of thermoplastic polyurethane and carbon nanofibers (CNFs) by systematically investigating the influences of TPU substrates (i.e., either electrospun nanofibers or solid thin film) and spray coating methods (i.e., either air-spray or electro-spray). It is found that the sensors with electro-sprayed CNFs conductive sensing layers generally show a higher sensitivity, while the influence of the substrate is not significant and there is no clear and consistent trend. The sensor composed of a TPU solid thin film with electro-sprayed CNFs exhibits an optimal performance with a high sensitivity (gauge factor ~28.2) in a strain range of 0–80%, a high stretchability of up to 184%, and excellent durability. The potential application of these sensors in detecting body motions has been demonstrated, including finger and wrist-joint movements, by using a wooden hand. Full article

It is a challenge to develop cost-effective strategy and design specific microstructures for fabricating polymer-based impact-resistance materials. Human shin bones require impact resistance and energy absorption mechanisms in the case of rapid movement. The shin bones are exciting biological materials that contain concentric circle structures called Haversian structures, which are made up of nanofibrils and collagen. The “soft and hard” structures are beneficial for dynamic impact resistance. Inspired by the excellent impact resistance of human shin bones, we prepared a sort of polyurethane elastomers (PUE) composites incorporated with rigid carbon nanofibers (CNFs) modified by elastic mussel adhesion proteins. CNFs and mussel adhesion proteins formed bone-like microstructures, where the rigid CNFs are served as the bone fibrils, and the flexible mussel adhesion proteins are regarded as collagen. The special structures, which are combined of hard and soft, have a positive dispersion and compatibility in PUE matrix, which can prevent cracks propagation by bridging effect or inducing the crack deflection. These PUE composites showed up to 112.26% higher impact absorbed energy and 198.43% greater dynamic impact strength when compared with the neat PUE. These findings have great implications for the design of composite parts for aerospace, army vehicles, and human protection. Full article

Polyurethane elastomers (PUE), with superior mechanical properties and excellent corrosion resistance, are applied widely to the protective capability of structures under low-speed impact. However, they are prone to instantaneous phase transition, irreversible deformation and rupture even arising from holes under high-speed impact. In this paper, mussel adhesion proteins were applied to modify carbon nanofibers (CNFs) in a non-covalent way, and creatively mixed with PUE. This can improve the dispersity and interfacial compatibility of nanofillers in the PUE matrix. In addition, the homogeneous dispersion of modified nanofillers can serve as “reinforcing steel bars”. The nanofillers and PUE matrix can form “mud and brick” structures, which show superb mechanical properties and impact resistance. Specifically, the reinforcement of 1.0 wt.% modified fillers in PUE is 103.51%, 95.12% and 119.85% higher than the neat PUE in compression modulus, storage modulus and energy absorption capability, respectively. The results have great implications in the design of composite parts for aerospace and army vehicles under extreme circumstances. Full article

Marine pollution due to spillage of hydrocarbons represents a well-known current environmental problem. In order to recover the otherwise wasted oils and to prevent pollution damage, polyurethane foams are considered suitable materials for their ability to separate oils from sea-water and for their reusability. In this work we studied polyurethane foams filled with carbon nanofibers, in varying amounts, aimed at enhancing the selectivity of the material towards the oils and at improving the mechanical durability of the foam. Polyurethane-based foams were experimentally characterized by morphological, surface, and mechanical analyses (optical microscopy observation, contact angle measurement, absorption test according to ASTM F726-99 standard and compression fatigue tests according to ISO 24999 standard). Results indicated an increase in hydrophobic behavior and a good oleophilic character of the composite sponges besides an improved selective absorption of the foam toward oils in mixed water/oil media. The optimal filler amount was found to be around 1 wt% for the homogeneous distribution inside the polymeric foam. Finally, the fatigue test results showed an improvement of the mechanical properties of the foam with the growing carbon filler amount. Full article

Pressure sensors have been widely used in electronic wearable devices and medical devices to detect tiny physical movements and mechanical deformation. However, it remains a challenge to fabricate desirable, comfortable wearing, and highly sensitive as well as fast responsive sensors to capture human body physiological signs. Here, a new capacitive flexible pressure sensor that is likely to solve this problem was constructed using thermoplastic polyurethane elastomer rubber (TPU) electrospinning nanofiber membranes as a stretchable substrate with the incorporation of silver nanowires (AgNWs) to build a composite dielectric layer. In addition, carbon nanotubes (CNTs) were painted on the TPU membranes as flexible electrodes by screen printing to maintain the flexibility and breathability of the sensors. The flexible pressure sensor could detect tiny body signs; fairly small physical presses and mechanical deformation based on the variation in capacitance due to the synergistic effects of microstructure and easily altered composite permittivity of AgNW/TPU composite dielectric layers. The resultant sensors exhibited high sensitivity (7.24 kPa⁻¹ within the range of 9.0 × 10⁻³ ~ 0.98 kPa), low detection limit (9.24 Pa), and remarkable breathability as well as fast responsiveness (<55 ms). Moreover, both continuously pressing/releasing cycle over 1000 s and bending over 1000 times did not impair the sensitivity, stability, and durability of this flexible pressure sensor. This proposed strategy combining the elastomer nanofiber membrane and AgNW dopant demonstrates a cost-effective and scalable fabrication of capacitive pressure sensors as a promising application in electronic skins and wearable devices. Full article

In the majority of photocatalytic applications, the photocatalyst is dispersed as a suspension of nanoparticles. The suspension provides a higher surface for the photocatalytic reaction in respect to immobilized photocatalysts. However, this implies that recovery of the particles by filtration or centrifugation is needed to collect and regenerate the photocatalyst. This complicates the regeneration process and, at the same time, leads to material loss and potential toxicity. In this work, a new nanofibrous membrane, g-C₃N₄/PMMA/PUR, was prepared by the fixation of exfoliated g-C₃N₄ to polyurethane nanofibers using thin layers of poly(methyl methacrylate) (PMMA). The optimal amount of PMMA was determined by measuring the adsorption and photocatalytic properties of g-C₃N₄/PMMA/PUR membranes (with a different PMMA content) in an aqueous solution of methylene blue. It was found that the prepared membranes were able to effectively adsorb and decompose methylene blue. On top of that, the membranes evinced a self-cleaning behavior, showing no coloration on their surfaces after contact with methylene blue, unlike in the case of unmodified fabric. After further treatment with H₂O₂, no decrease in photocatalytic activity was observed, indicating that the prepared membrane can also be easily regenerated. This study promises possibilities for the production of photocatalytic membranes and fabrics for both chemical and biological contaminant control. Full article