Thermoplastic Polyurethane Matrix Research Articles

Hybrid Nanocomposites of Cellulose/Carbon-Nanotubes/Polyurethane with Rapidly Water Sensitive Shape Memory Effect and Strain Sensing Performance.

In this work, a fast water-responsive shape memory hybrid polymer based on thermoplastic polyurethane (TPU) was prepared by crosslinking with hydroxyethyl cotton cellulose nanofibers (CNF-C) and multi-walled carbon nanotubes (CNTs). The effect of CNTs content on the electrical conductivity of TPU/CNF-C/CNTs nanocomposite was investigated for the feasibility of being a strain sensor. In order to know its durability, the mechanical and water-responsive shape memory effects were studied comprehensively. The results indicated good mechanical properties and sensing performance for the TPU matrix fully crosslinked with CNF-C and CNTs. The water-induced shape fixity ratio (Rf) and shape recovery ratio (Rr) were 49.65% and 76.64%, respectively, indicating that the deformed composite was able to recover its original shape under a stimulus. The TPU/CNF-C/CNTs samples under their fixed and recovered shapes were tested to investigate their sensing properties, such as periodicity, frequency, and repeatability of the sensor spline under different loadings. Results indicated that the hybrid composite can sense large strains accurately for more than 103 times and water-induced shape recovery can to some extent maintain the sensing accuracy after material fatigue. With such good properties, we envisage that this kind of composite may play a significant role in developing new generations of water-responsive sensors or actuators.

The dispersion of CNT in TPU matrix with different preparation methods: solution mixing vs melt mixing

Melt mixing and solution mixing are two commonly used methods for the preparation of polymer nanocomposites. In this work, thermoplastic polyurethane (TPU) composites with unmodified MWCNTs and carboxyl MWCNTs (MWCNT-COOH) were prepared using melt mixing and solution mixing. The dispersion of filler in TPU matrix and the macro-properties of composites under different processing conditions were systematically investigated. It was found that for pristine MWCNTs, a better dispersion was obtained using solution method at relatively low content of fillers (≤2.5 wt%); but when the content of MWCNT was above 2.5 wt%, melt mixing under high shear force was more effective to achieve a homogeneous dispersion. The similar result was confirmed in TPU/MWCNT-COOH composites, with the critical concentration shifted to 5.0 wt%, indicating that the interaction between CNT and TPU also played role on the dispersion of CNT in TPU matrix via solution mixing. Our finding is important for the preparation of polymer/CNT nanocomposites with good dispersion depending on the filler content and mixing methods.

The effect of two‐dimensional d‐Ti3C2 on the mechanical and thermal conductivity properties of thermoplastic polyurethane composites

AbstractIn this study, Ti3C2 was delaminated into monolayer or few‐layer d‐Ti3C2 nanosheets, followed by preparation of d‐Ti3C2/thermoplastic polyurethane (TPU) composites. The products were characterized by X‐ray diffraction and field emission scanning electron microscopy. The effects of d‐Ti3C2 loading on the thermal and mechanical properties of the composites were investigated and the fracture morphology was analyzed. Results showed that the prepared d‐Ti3C2 was a monolayer or few‐layer nanosheets and the monolayer thickness is about 1.2 nm. The two‐dimensional d‐Ti3C2 was uniformly dispersed in the TPU matrix. The addition of d‐Ti3C2 nanosheets increased the thermal conductivity of TPU and also improved the mechanical properties of the matrix. When d‐Ti3C2 loading was 1 wt%, the specific strength and specific elongation were improved by about 29% and 53%, meanwhile the dissipated energies increased by 0.3 kJ/m3.

Rheological investigation of carbon-based hybrid polyurethane nanocomposites with continuous networks

Carbon-based fillers were used as reinforcement for thermoplastic polyurethane (TPU) matrix. For the first time the rheological behavior of hybrid polyurethane nanocomposite has been surveyed and the formation of continuous network of two carbon-based fillers has been reported. Nanocomposites containing multi-walled carbon nanotubes (MWCNTs), carbon fibers (CFs) and MWCNTs/CFs were prepared through melt compounding method and evaluated with various techniques including microscopy, spectroscopy and comprehensive rheological analyses. Linear rheological methods such as strain, frequency, temperature and time sweeps, and non-linear flow curve method were adopted to study the viscoelastic properties of the nanocomposites. Attenuated total reflectance Fourier transform infrared spectroscopy showed that MWCNTs had higher interactions with TPU hard segments due to their high aspect ratio, whereas CFs had low interactions. In hybrid nanocomposite, a continuous network of carbon-based fillers was created which acted as a surface for nucleation of hard segment and induced the highest influence on viscoelastic behavior of resulting nanocomposites. Based on the microscopy analyses, existence of co-continuous morphology was observed for hybrid nanocomposite. Moreover, relationship between the structure of nanofillers and formation of microphase separated domains at various nanofiller contents was discussed. At first, the rheological behavior of each nanocomposite was separately studied. To conclude, the results corroborated that CFs and MWCNTs formed a network of carbon-based structure and changed the viscoelastic properties of hybrid nanocomposites.

An improved technique for dispersion of natural graphite particles in thermoplastic polyurethane by sub-critical gas-assisted processing

Dispersing fillers uniformly is the main technological challenge when considering nanocomposites. In this paper, a novel and efficient sub-critical gas-assisted processing (SGAP) technique is explored—an environmentally benign process that utilizes compressed CO2 to help effectively disperse aggregated natural graphite particles (NGPs) (3 wt%) in a thermoplastic polyurethane (TPU) matrix. A twin-screw extruder (TSE) equipped with a simple CO2 injection unit consisting of a standard gas cylinder, regulator, valve, and metal hose is employed for the melt mixing. Results from the structural, thermal, rheological, mechanical, microcellular injection molding, dielectric, and thermal conductive properties of the SGAP pellets, in addition to the resultant TPU/NGP nanocomposites, confirmed significantly improved dispersion compared to those obtained via conventional melt blending in the TSE. This technique offers a simple, cost-effective approach to the large-scale production of high-performance polymer nanocomposites without the requirement for complicated processing steps such as supercritical fluid (SCF) processes or chemical treatments.

Strong, stretchable and ultrasensitive MWCNT/TPU nanocomposites for piezoresistive strain sensing

We report strong, stretchable and ultrasensitive thermoplastic polyurethane (TPU) nanocomposites reinforced with multiwalled carbon nanotubes (MWCNT) for piezoresistive strain sensing. Uniform dispersion of MWCNT in TPU matrix offers low percolation threshold (0.1 wt%) and superior electrical conductivity. MWCNT/TPU nanocomposites exhibit different sensitivities and measurable strain ranges depending upon MWCNT concentration. Static stretch experiments reveal nearly linear piezoresistive response up to 15%, 35% and 45% strain with gauge factor (GF) of 22, 8.3 and 7.0 for 0.3, 0.5 and 1.0 wt% MWCNT loaded TPU nanocomposites, respectively. With further stretching, TPU nanocomposites evince strain-dependent GF of 6395, 6423 and 7935 at 35%, 95% and 185% strain for 0.3, 0.5 and 1.0 wt% MWCNT loading, respectively. Furthermore, we observe improvements in tensile strength, yield strength and Young's modulus of 51%, 37% and 23% for 0.1 wt % MWCNT loading and 10%, 83% and 66% for 0.3 wt % MWCNT loading, respectively. Cyclic stretch/release tests for 0.3 wt% MWCNT loaded nanocomposites show good recoverability and reproducibility over 100 cycles up to a strain-amplitude of 50%. Ultrahigh GF of MWCNT/TPU nanocomposites compared to extant work together with their tuneable sensitivity in both small and large strain regimes, enhanced strength and ease of fabrication make them attractive for high performance strain sensing devices.

Effect of 5-15% Carbon Black Reinforcement on Mechanical Properties and Resistivity of Polyurethane Composites

This research investigated the effects of carbon black-reinforced thermoplastic polyurethane matrix composite with variation of 5, 10, and 15 vol.% on mechanical properties and electrical resistance. The composites were produced using injection molding process with temperature of 193 °C, pressure of 30 bar and injection speed of 176 mm/sec. Characterization of composites were conducted by hardness and tensile testing, electrical resistivity measurement and SEM examinations. The results showed that the highest tensile strength of composite of 20.44 MPa is obtained with carbon black 10 vol.% reinforcement. The hardness improved with the increase of carbon black reinforcement, which the highest hardness was produced on carbon black 15 vol.% composite by 89.5 Shore A. The lowest resistivity was achieved in polyurethane composite reinforced with 15 vol.% carbon black of 8.20 x 105 Ω.

A novel strategy for simultaneously improving the fire safety, water resistance and compatibility of thermoplastic polyurethane composites through the construction of biomimetic hydrophobic structure of intumescent flame retardant synergistic system

The water resistance, compatibility and anti-dripping performance of flame retardant thermoplastic polyurethane (TPU) composites have still been a challenge in the fire science. Inspired by the hydrophobic surface structure of biomaterials, the hydrophobic charring agent N-methyl triazine-piperazine copolymer (MTPC) and modified magnesium oxide (MgO) were assembled on ammonium polyphosphate (APP) surface to prepare the hydrophobic intumescent flame retardant (HIFR) system. The constructed HIFR system presented excellent hydrophobic performance with the water contact angle of 139°. The HIFR was incorporated into TPU matrix. The tensile strength and elongation at break of TPU/10 wt% HIFR composites increased by 48 and 106% compared with that of TPU/10 wt% APP. Meanwhile, the specimens of TPU/10 wt% HIFR composites before and after water resistance tests achieved UL-94 V-0 rating without drippings and the limiting oxygen index value was 27.5 and 27.3%. TPU/HIFR composites still maintained excellent flame retardancy and mechanical properties after water treatment. Cone calorimeter tests revealed that the peak of heat release and smoke production, and CO yield of TPU/10 wt% HIFR composites were significantly decreased with the reduction of 87.0, 63.2 and 28.6% compared with that of neat TPU. The incorporation of HIFR effectively enhanced the fire safety for TPU composites. The investigation of flame retardant mechanism for TPU/HIFR demonstrated that HIFR catalyzed the TPU matrix charring in advance and the generated compact, homogeneous and partial graphitized char layer exerted barrier effect in condensed phase, and the released inert gases evoked dilution effect in gas phase. This presented work provided a novel promising approach for preparing TPU materials with excellent comprehensive performance as well as water resistance and highly flame retardant efficiency.

Improved dielectric and actuated performance of thermoplastic polyurethane by blending with XNBR as macromolecular dielectrics

In the present study, carboxylated nitrile rubber (XNBR) with high dielectric constant (εr) and low elastic modulus (Y) was introduced into thermoplastic polyurethane (TPU) with good mechanical properties to prepare macroscopic homogeneous high performance dielectric elastomer (DE) blends. The results show that the XNBR macromolecules can disrupt the N-H/C=O hydrogen bonds of TPU, leading to the increase in dipole polarizability of TPU matrix. On the other hand, the formation of hydrogen bonds between XNBR and TPU increases the interfacial interaction and thus the interfacial polarizability of XNBR/TPU blends. The improvement of both the dipole polarizability and the interfacial polarizability result in the significant improvement of εr of TPU with increasing the content of XNBR. Meanwhile, the Y of TPU is decreased due to the disruption of hydrogen bonds of TPU and the softening effect of XNBR. The simultaneous increase in εr and decrease in Y of TPU results in the large increase in electromechanical sensitivity (β) and actuated strain at low electric field of XNBR/TPU blends. Interestingly, the εr at 103 Hz, the β and the actuated strain at certain electrical field of the blend with XNBR/TPU blending ratio of 80/20 is even higher than that of pure XNBR, which is attributed to the co-continuous structure of this blend as well as the synergetic effect of the increase in dipole polarizability of both TPU and XNBR and the increase in interfacial polarizability. Comparing with our previous study on TPU DE blend by adding low molecular weight plasticizer, XNBR/TPU macromolecular DE blend show better overall performance such as higher mechanical strength, higher breakdown strength and better stability, thus are more likely to be applied in biological and medical fields, where a low electric field is required.

An effective mono-component intumescent flame retardant for the enhancement of water resistance and fire safety of thermoplastic polyurethane composites

Flame-retardant thermoplastic polyurethane (TPU) composites are usually used in the wire and cable areas, but the water resistance of composites seriously restrains its further application. Herein, a mono-component intumescent flame retardant dimelamine pyrophosphate (DMPY) was successfully synthesized and incorporated into TPU matrix. The fire safety, mechanical performance, water resistance and flame retarded mechanisms of TPU/DMPY composites were systematically investigated. When 15 wt% DMPY was incorporated, the samples of TPU/DMPY fulfilled UL-94 V-0 grade during vertical burning tests with the limiting oxygen index of 27.3%. The blowing-out effect appeared during vertical burning tests and it improved the flame retardant performance of composites. The integrated, dense and partially graphitized char layer was produced on TPU/DMPY composites surface during combustion. Moreover, the release of noncombustible gases exerted diluted effect in gas phase. As a results, the production of heat, toxicity and smoke were significantly suppressed and led to good fire safety performance of TPU composites. Furthermore, the TPU/DMPY remained satisfied flame retardancy and mechanical performance after the samples were soaked into 70 °C for 168 h and dried to a constant weight. The TPU/DMPY composites with good comprehensive performance as well as fire safety, water resistance and mechanical performance were prepared in this investigation, which would bring more chance for wider application of TPU composites in key fields.

Properties of two-dimensional Ti3C2 MXene/thermoplastic polyurethane nanocomposites with effective reinforcement via melt blending

Realizing a homogeneous distribution of two-dimensional nanosheets in polymer matrix, avoiding their agglomeration, has been a key scientific challenge in fabricating high-performance polymer nanocomposites. Herein, we report a simple and eco-friendly strategy for preparing thermoplastic polyurethane (TPU) nanocomposites with homogeneously dispersed Ti3C2 MXene nanosheets. In this method, MXene is first pretreated with polyethylene glycol (PEG) and then subjected to melt blending with TPU. These processes effectively exfoliate MXene nanosheets, which are then well dispersed inside the TPU matrix. The MXene/TPU nanocomposites show mechanical and thermal properties that are superior to those of pristine TPU. Tensile strength and storage modulus increase by 47.1% and 39.8% at MXene loading values of 0.5 wt%. The onset degradation temperature of the nanocomposites increases by 13.1 °C, whereas the maximum degradation temperature increases by 20.3 °C at 0.5 wt% MXene loading. This study may provide a promising strategy for manufacturing MXene-based polymer nanocomposites with effective reinforced properties at the industrial level.

Thermoplastic polyurethane/laponite nanocomposite for reducing impact sound in a floating floor

An effective way to reduce impact sound in buildings is to install a floating floor consisting of a floating slab separated from the structural slab by a continuous viscoelastic layer. Although a considerable amount of work has been reported on nanomaterials in the past decades, the impact sound reduction performance of polymer/clay nanocomposites has not been specifically addressed in the literature. In this paper, we report the synthesis and characterization of a nanocomposite made of thermoplastic polyurethane (TPU) with laponite clay filler and its potential use for reducing impact sound in floating floor technology. Samples were prepared with laponite content ranged between 0.5 and 10 wt% for each nanocomposite synthesized using a solvent solution mixing process. The characterization of the nanocomposites confirmed that the clay content in the TPU matrix has significant impact on the viscoelastic properties. In particular, the incorporation of 5–10 wt% laponite clay in the TPU matrix increased mechanical damping and reduced dynamic stiffness as compared to the pristine TPU. The experimental results were compared with a constitutive model that extends the Cremer-Vér model. The results predicted a considerable improvement of the impact sound insulation at the resonance frequency when the nanocomposite is used as a continuous viscoelastic layer supporting the floating slab. These results were attained without significantly increasing the total weight of the floating layer.

Programing polyurethane with systematic presence of graphene-oxide (GO) and reduced graphene-oxide (rGO) platelets for adjusting of heat-actuated shape memory properties

We fabricated shape memory composites based on thermoplastic polyurethane (TPU) containing three types of graphene, that is, graphene-oxide (GO), reduced graphene-oxide (rGO) and hybrid GO:rGO (ratio 1:1) to study their mechanical and shape memory properties. Tailoring a bridge between microstructure and macro-properties of TPU composites comprising 1, 2 and 5 wt% filler concentration was the primary aim of this work. Incorporation of GO and rGO platelets into the TPU matrix augmented the modulus, elongation at break and breaking stress compared to that of pristine TPU. Besides, the TPU/rGO composites revealed greater young modulus, %elongation, storage modulus, and %crystallinity compared to TPU/GO composites at similar filler content. In particular, the TPU/GO:rGO composites displayed the synergic improvement in dynamic and static mechanical properties owing to the systematic localization GO and rGO platelets in hard and soft segments of TPU, respectively. Interestingly, this localization was thermodynamically predicted by the solubility parameter of components and approved with microscopic observation. The TPU composite behavior was further examined by relaxation stress analysis. While the GO platelets have no significant influence on shape recovery behavior as compared to rGO filled composites, on the other hand, the shape fixation is deteriorated by adding the rGO platelets. The shape memory assessment clarified that the simple TPU composites comprising GO(2 wt%) and rGO(5 wt%) have the highest value in shape fixity and shape recovery, respectively. Noteworthy, both shape fixity and recovery of TPU composites improved when simultaneously using the rGO and GO platelets (GO:rGO) as hybrid filler. The shape recovery and fixity value of 5 wt% TPU composite containing hybrid GO:rGO is 96.7% and 99.1%, respectively, which it has increased up 1.12, 1.05 and 1.02-fold in shape recovery that of neat TPU, 5 wt% TPU composite containing GO and rGO, respectively. This study proves that incorporation of hybrid GO:rGO into shape memory TPU matrix can be employed effectively to attain superior mechanical strength, the excellent shape fixity and high actuation value.

Porous 3-D thermoplastic polyurethane (TPU) scaffold modified with hydroxyapatite (HA) nanoparticles using an ultrasonic method

In this work, a 3-D porous hydroxyapatite (HA)-decorated thermoplastic polyurethane (TPU) scaffold with high porosity and excellent biocompatibility was successfully fabricated using a simple ultrasonic method. It was found that HA nanoparticles were successfully introduced onto the surface of the TPU scaffold, and a strong interaction occurred between the HA nanoparticles and the TPU matrix. The porosity was calculated to be about 87%. The water contact angle decreased from 121.1° for TPU to 44.6° for HA-decorated TPU scaffolds. The water absorption and mechanical properties of HA-decorated TPU scaffolds were significantly higher than those of TPU scaffolds. Compared with TPU scaffolds, the addition of HA nanoparticles effectively improved the attachment and growth of mouse embryonic osteoblast cells (MC3T3-E1) cultured on the HA-decorated TPU scaffolds. These results suggest that HA-decorated TPU scaffolds possess great potential to be used as tissue engineering scaffolds. Furthermore, the ultrasonic technique could be used as a simple, effective, and universal method for decorating tissue engineering scaffolds.

A comparison of thermoplastic polyurethane incorporated with graphene oxide and thermally reduced graphene oxide: Reduction is not always necessary

ABSTRACTDespite wide applications of reduced graphene‐oxide (GO)‐reinforced polymer‐based composites, the necessity of the reduction procedure toward GO is still controversial. In this article, thermoplastic polyurethane (TPU) composites incorporated with GO and thermally reduced graphene oxide (TGO) were fabricated. GO and TGO exhibited different effects on crystallization behaviors, and mechanical and thermal properties of the TPU matrix. With 2.0 wt % filler loading, TPU composite reinforced by GO (TPU‐GO‐2 wt %) exhibited better thermal stability than that reinforced by TGO (TPU‐TGO‐2 wt %). The interfacial interaction between the nanofillers and the TPU matrix as well as their influence on the mobility of TPU chains were investigated, which proved that GO is superior to TGO in improving interface adhesion and maintaining crystallization of the TPU matrix. Compared with TPU‐TGO‐2 wt %, improved mechanical properties of TPU‐GO‐2 wt % were also evidenced owing to more oxygen‐containing groups. This work demonstrates that the reduction of GO is not always necessary in fabricating polymer composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47745.

Selective Laser Sintering Fabricated Thermoplastic Polyurethane/Graphene Cellular Structures with Tailorable Properties and High Strain Sensitivity

Electrically conductive and flexible thermoplastic polyurethane/graphene (TPU/GE) porous structures were successfully fabricated by selective laser sintering (SLS) technique starting from graphene (GE)-wrapped thermoplastic polyurethane (TPU) powders. Several 3D mathematically defined architectures, with porosities from 20% to 80%, were designed by using triply periodic minimal surfaces (TMPS) equations corresponding to Schwarz (S), Diamond (D), and Gyroid (G) unit cells. The resulting three-dimensional porous structures exhibit an effective conductive network due to the segregation of graphene nanoplatelets previously assembled onto the TPU powder surface. GE nanoplatelets improve the thermal stability of the TPU matrix, also increasing its glass transition temperature. Moreover, the porous structures realized by S geometry display higher elastic modulus values in comparison to D and G-based structures. Upon cyclic compression tests, all porous structures exhibit a robust negative piezoresistive behavior, regardless of their porosity and geometry, with outstanding strain sensitivity. Gauge factor (GF) values of 12.4 at 8% strain are achieved for S structures at 40 and 60% porosity, and GF values up to 60 are obtained for deformation extents lower than 5%. Thermal conductivity of the TPU/GE structures significantly decreases with increasing porosity, while the effect of the structure architecture is less relevant. The TPU/GE porous structures herein reported hold great potential as flexible, highly sensitive, and stable strain sensors in wearable or implantable devices, as well as dielectric elastomer actuators.

Improved thermal conductivity of thermoplastic polyurethane via aligned boron nitride platelets assisted by 3D printing

Thermal management is of importance to microelectronics. Owning both excellent thermal conduction and electrical insulation, hexagonal boron nitride (hBN) platelets are widely used in polymer matrices. While the thermal properties rely on the orientation of hBN platelets in polymer matrices significantly. Herein, we report that high thermal conductive hBN filled thermoplastic polyurethane (TPU) composites can be achieved by a fused deposition modeling 3D printing technique. The hBN platelets show excellent alignment along printing direction in TPU matrix due to the shear-inducing effect of printing. The sample along printing direction at filler loading of 25.9 vol% (40 wt%) exhibits the thermal conductivity up to 2.56 Wm−1 K−1 at 100 °C along printing direction, i.e. 10- and 2.8-time enhancement, compared to those of neat TPU and hBN/TPU sample tested along thickness direction. The surface temperature distribution of samples with various heating durations is also presented. The effects of some key parameters, i.e. nozzle diameter, printing speed as well as filler loading, on the alignment level of hBN are also investigated. Finally, the alignment level of the platelets is predicted by effective medium approximation, which is consistent with that measured by small angle X-ray scattering.

Enhanced Solid Particle Erosion Properties of Thermoplastic Polyurethane‐Carbon Nanotube Nanocomposites

AbstractA co‐coagulation method combined with hot pressing technique is successfully applied to fabricate thermoplastic polyurethane (TPU) nanocomposites with different contents of carbon nanotubes (CNTs). Obviously, the mechanical and thermal properties of the nanocomposites are improved with increasing the CNT content. In addition, the existence of hydrogen bonding between CNTs and polymer matrix is demonstrated. Furthermore, the influences of impact parameters on solid particle erosion behavior are investigated systematically. The surface roughness and line roughness are also investigated to illustrate the mechanism of solid particle erosion. As elastic nanocomposites, the maximum and minimum erosion rate (ER) occur at 30° and 90°. The ER is relatively small when the impact velocity is at 10 m s−1, then is increased rapidly between 20 and 30 m s−1. As the size of impact particles increases to 300 µm, a rapid increase of ER occurs between 10 and 20 m s−1. All these results indicate CNTs improve the erosion resistance of TPU matrix.

A highly stretchable large strain sensor based on PEDOT–thermoplastic polyurethane hybrid prepared via in situ vapor phase polymerization

Strain sensors based on percolated networks of poly(3,4-ethylenedioxythiophene) (PEDOT) in thermoplastic polyurethane (TPU) matrix fabricated through in situ vapor phase polymerization (VPP) is reported. The hybrid made of elastomer and conductive polymer shows uniform PEDOT distribution on the surface and inner side of the TPU due to the effective penetration, diffusion, and polymerization of EDOT. Performance of sensors using two kinds of oxidants (FeCl3 or iron(III) p-toluenesulfonate(FTS)) are compared and the concentration is varied to obtain the best electromechanical properties. Amount of PEDOT increases with increasing amount of oxidant: thereby improving the electrical conductivity, while the elasticity of the hybrid decreases. The elasticity reduction phenomenon is diminished when FTS is used due to the plasticizer effect of the tosylate ion on the TPU. The performances of PEDOT–TPU hybrids prepared with FTS are excellent in the terms of stretchability (>300%), gauge factor (GF > 10 @ strain 100%), resistance variation reproducibility under various strain modes, small hysteresis, and durability (>1000 cycle). With the electromechanical performance, as well as cheap and scalable production, the PEDOT/TPU sensor holds tremendous prospects on flexible and stretchable devices for human motion monitoring, as well as present strategies on architecture of conductive soft materials.

Effect of MWCNT content on the mechanical and strain-sensing performance of Thermoplastic Polyurethane composite fibers

Stretchable conductive fibers have attracted significant attention due to their ability to be directly woven into or stitched onto fabrics, making them ideal for use in the design of integrated wearable strain sensors. Here, we report on a highly stretchable multi-walled carbon nanotube (MWCNT)/Thermoplastic Polyurethane (TPU) fiber produced via a wet spinning process. The effects of MWCNT content and alignment on the structural, mechanical, electrical and strain-sensing properties of the composite fibers were investigated. The highest conductivity (6.77 S cm−1), tensile strength (28 MPa) and maximum elongation at break (565%) were obtained by controlling the MWCNT content. Gauge factor (GF) values were also affected by the content and MWCNT alignment in the composite fibers, as these parameters determine the change in the effective contact area and number of conductive paths available during stretching. The well-aligned MWCNT/TPU fiber showed a high GF value of 5200. Wearable strain sensors capable of obtaining real-time mechanical feedback for various human motion detections with different GFs and working strain ranges could be realized by controlling the MWCNT concentrations in the TPU matrix.