Properties Of Thermoplastic Polyurethane Research Articles

Investigating the Effect of Chain Extender on the Phase Separation and Mechanical Properties of Polybutadiene-Based Polyurethane.

The thermodynamic incompatibility between the soft and hard segments of thermoplastic polyurethane (TPU) results in a microphase-separated behavior and excellent mechanical properties. However, the effect of the chain extender on the degree of microphase separation (DMS) and the resultant mechanical properties of TPU have not been well studied because of the complex interactions between the soft and hard segments. Herein, hydroxyl-terminated polybutadiene-based TPUs(HTPB-TPUs) without hydrogen bonding between the soft and hard segments are synthesized using hydroxyl-terminated polybutadiene, toluene diisocyanate, and four different chain extenders, and the effect of the chain extender structure on DMS is analyzed experimentally using a combination of analytical techniques. Furthermore, the solubility parameters of the soft and hard segments, glass transition temperatures, and hydrogen-bond density of the HTPB-TPUs, are computed using all-atom molecular dynamics simulations. The results clearly reveal that the chain extender significantly affects the DMS and thus the mechanical properties of HTPB-TPUs. This study paves the way for studying the relationship between the structure and properties of TPU.

Preparation of phosphorus-containing organic-hybrid layered double hydroxide as a flame retardant for thermoplastic polyurethane

Developing polymers with both flame-retardant and smoke-suppressing properties is a great challenge in the field of fire-safety thermoplastic polyurethane (TPU). This study involved synthesizing a synergistic organic-hybrid layered double hydroxide (O-LDH) and phosphorus/nitrogen-containing substance (PD) inspired by the observed synergistic effect between them. The incorporation of PD significantly enhanced the flame-retardant properties of TPU in conjunction with cobalt/aluminum- layered double hydroxide. The composite containing 10 wt% O-LDH achieved a limiting oxygen index of 26.5% and met the vertical burning V-0 rating. Moreover, the heat and smoke release were decreased compared to pure TPU in cone calorimeter tests. The systematic characterization of the synergistic flame-retardant mechanism emphasized the crucial contribution of cobalt and phosphorus species in catalyzing charring effects, resulting in the compact and highly carbonized char layer in the condensed phase. The incorporation of the hybrid flame retardant significantly enhanced the advancement of the flame-retardant TPU materials.

Tribological evaluation of thermoplastic polyurethane-based bearing materials under water lubrication: Effect of load, sliding speed, and temperature

Polymers are widely used in bearing applications. In the case of water-lubricated stern tube bearings, thermoplastic polyurethane (TPU)-based composites are used due to their excellent wear resistance, corrosion resistance, and tunable mechanical properties. Their tribological performance, however, depends on operating conditions. In this work, TPU was blended with carbon fiber, graphene platelet, and ultra-high molecular weight polyethylene (UHMWPE). Friction tests of TPU based-composites against copper countersurface were carried out in water to mimic the actual operating conditions of the bearing. Most of the resulting contacts were in the boundary lubrication regime, in which friction was attributed to both contact mechanics of asperities as well as water lubrication. Our results show that the viscoelasticity of TPU has a considerable impact on its tribological performance. Water lubrication at 50 °C promotes the softening of polymer surface material during sliding, resulting in higher fluctuation in the coefficient of friction and wear loss. This is attributed to the reduced thermomechanical properties. In addition, Schallamach waviness is observed on worn surface. The tribological properties of TPU are significantly improved by the inclusion of carbon fiber, graphene platelet, and UHMWPE. The formation of graphene transfer-layers and UHMWPE transfer film reduces friction and wear loss, while the inclusion of carbon fiber enhances wear resistance due to improved mechanical properties and load bearing capacity.

Optimizing TPU performance: The role of mold temperature on injection molding of TPU

AbstractThis study explores the influence of mold temperatures below 60°C on thermoplastic polyurethane (TPU) properties during injection molding, focusing on phase separation and its impact on mechanical, thermal, and viscoelastic properties. Using a combination of micro‐indentation, temperature scanning stress relaxation, and conventional characterization methods, the research highlights how increased mold temperatures promote more distinct phase separation, enhancing mechanical stability and physical properties. The novel use of micro‐indentation revealed a gradient in material stiffness from the surface to the core of injection‐molded samples, attributed to differential cooling rates and shear forces, which affect phase separation and crystallinity of the hard domains. These insights are critical for applications requiring specific surface properties and underscore the importance of understanding the interplay between chemical composition and processing conditions for optimizing TPU properties. Furthermore, the paper shows that tensile testing, differential scanning calorimetry, and Shore hardness cannot quantify the effects of mold temperatures below 60°C. The research highlights the influence and importance of chemical composition, rheological history, and thermal history on the properties of TPU.

Enhancing flame retardancy, anti‐impact, and corrosive resistance of TPU nanocomposites using surface decoration of α‐ZrP

AbstractThe development of polyurethane composites with significant flame retardancy and corrosion resistance for widening its practical application is a great importance. In this study, supramolecular wrapped α‐ZrP (MCP@ZrP) was prepared via self‐assembly of melamine, cobalt ions (Co2+) and phytic acid (PA) on the surfaces of α‐zirconium phosphate (α‐ZrP). It was found that both compatibility and dispersion of α‐ZrP sheets in thermoplastic polyurethane (TPU) matrices were improved with the incorporation of organic supramolecular components in TPU/MCP@ZrP nanocomposites. Moreover, their fire‐retardant characteristic was significantly enhanced, along with effective suppression of smoke and toxic gas emission. By adding 5 wt% MCP@ZrP, peak heat release rate, total heat release, total smoke production, and total CO production of such nanocomposites were reduced by 35.66%, 18.01%, 15.52%, and 41.42%, respectively. The generation of a continuous and dense char layer benefited from well‐dispersed MCP@ZrP nanohybrids, which resulted in tortuous effect to impede heat diffusion and prevent the evaporation of volatile gasses. By means of the barrier effect of ZrP, TPU/MCP@ZrP composite films also showed improved anticorrosion performance. Effective interfacial adhesion, achieved by combining MCP supermolecules and α‐ZrP sheets, offers a viable approach to improve protective properties of TPU nanocomposites.Highlights Supramolecular‐wrapped α‐ZrP was prepared via self‐assembly strategy. MCP@ZrP showed good dispersion and interface adhesion within TPU matrices. MCP@ZrP enhanced the flame retardancy and mechanical performance of TPU. MCP@ZrP preventing smoke and toxic gas evaporation.

Research on Fatigue Self-healing of Asphalts Modified by Thermoplastic Polyurethane (TPU) with Different Soft Segments

Research on asphalt fatigue and self-healing performance can more accurately model the damage and self-healing evolution principles in practical applications. In order to analyze the rationality of evaluation indexes based on rheology to evaluate the self-healing properties of TPU modified asphalt, a dynamic shear rheometer (DSR) was used in this study to perform time, temperature, and frequency sweep tests of TPU modified asphalt for analyzing the fatigue self-healing properties of TPU modified asphalt over a broader range of temperatures and loading frequencies. This method can improve the accuracy of the fatigue failure determination criteria of TPU modified asphalt and clarify the material performance parameters of TPU asphalt modifiers. The results showed that the increase in hard segment content (Ch) and isocyanate radical index (r) can effectively alleviate the decrease in shear deformation resistance of modified asphalt caused by the increase in N (load repetition). Nf50 (the number of loads when the normalized modulus drops to 0.5) is more suitable to evaluate the fatigue life of TPU modified asphalt compared with Np20 (the number of loads when the DER-N curve is offset by 20% deviation from the linear undamaged line) and N2 (the number of load times corresponding to the intersection point of the tangent line of the DER–N fitted curve and the undamaged line). The degree of self-healing will also increase with the increase in Ch and r. Besides, the higher the healing temperature and the healing time, the longer the fatigue life. The effects of the self-healing evaluation index (HI) on the self-healing index of TPU modified asphalt were as follows: healing temperature > healing time > soft segment >Ch >r > degree of damage > degree of aging > degree of self-healing.

Dynamic Characterization of a Low-Cost Fully and Continuously 3D Printed Capacitive Pressure-Sensing System for Plantar Pressure Measurements.

In orthopedics, the evaluation of footbed pressure distribution maps is a valuable gait analysis technique that aids physicians in diagnosing musculoskeletal and gait disorders. Recently, the use of pressure-sensing insoles to collect pressure distributions has become more popular due to the passive collection of natural gait data during daily activities and the reduction in physical strain experienced by patients. However, current pressure-sensing insoles face the limitations of low customizability and high cost. Previous works have shown the ability to construct customizable pressure-sensing insoles with capacitive sensors using fused-deposition modeling (FDM) 3D printing. This work explores the feasibility of low-cost fully and continuously 3D printed pressure sensors for pressure-sensing insoles using three sensor designs, which use flexible thermoplastic polyurethane (TPU) as the dielectric layer and either conductive TPU or conductive polylactic acid (PLA) for the conductive plates. The sensors are paired with a commercial capacitance-to-voltage converter board to form the sensing system. Dynamic sensor performance is evaluated via sinusoidal compressive tests at frequencies of 1, 3, 5, and 7 Hz, with pressure levels varying from 14.33 to 23.88, 33.43, 52.54, and 71.65 N/cm2 at each frequency. Five sensors of each type are tested. Results show that all sensors display significant hysteresis and nonlinearity. The PLA-TPU sensor with 10% infill is the best-performing sensor with the highest average sensitivity and lowest average hysteresis and linearity errors. The range of average sensitivities, hysteresis, and linearity errors across the entire span of tested pressures and frequencies for the PLA-TPU sensor with 10% infill is 11.61-20.11·10-4 V/(N/cm2), 11.9-31.8%, and 9.0-22.3%, respectively. The significant hysteresis and linearity error are due to the viscoelastic properties of TPU, and some additional nonlinear effects may be due to buckling of the infill walls of the dielectric.

Impact of Soft Segment Composition on Phase Separation and Crystallization of Multi-Block Thermoplastic Polyurethanes Based on Poly(butylene adipate) Diol and Polycaprolactone Diol

In this work, we explore the influence of soft segment structure on the crystallinity and phase separation of semicrystalline multi-block thermoplastic polyurethanes (TPUs) based on poly(butylene adipate) diol, polycaprolactone diol, and their mixture. According to thermal and structural analyses, the crystal growth rate and degree of crystallinity decrease with an increase in the PCL/PBA ratio and reach a minimum at the equimolar composition of polyesters. A reduction in crystal phase content leads to an improvement in elastomeric behavior. TPU samples with high PCL content demonstrate enhanced crystallinity but a lower melting temperature compared to TPU with PBA crystals. Crystallization of TPU below room temperature results in an enhancement of total crystallinity and a change in the phase composition of the PBA block. The difference in semicrystalline morphology and crystallization kinetics can be explained by the efficiency of phase separation and the density of hydrogen bonding between soft and hard segments. Our findings show that the ratio of the two crystallizable polyesters, combined with the choice of crystallization temperature, allows for independent control over the melting temperature and the overall degree of crystallinity of the TPUs. This significantly impacts the mechanical characteristics of the materials. The effect of adding a second crystallizable polyester on the crystallization behavior, phase composition, and mechanical properties of TPU is discussed for the first time.

Mechanical and tribological characterization of 3D printed-cryogenically treated thermoplastic polyurethane

In knee replacement surgery, the longevity of implants, particularly the plastic spacer between the femur and tibial metallic component, has profound implications. Traditionally, Ultra-High Molecular Weight Polyethylene (UHMWPE) has been the material of choice, yet its susceptibility to rapid wear necessitates the exploration of alternatives. Among these, Thermoplastic Polyurethane (TPU) is a promising candidate. This study delves into the transformative impact of deep cryogenic treatment (DCT) on the tribological, mechanical, and surface attributes of Fused Deposition Modeling (FDM) - produced TPU.Key findings unveil a substantial enhancement in the wear performance of DCT-treated TPU compared to its untreated counterpart. Moreover, extrusion temperature (ET) and print speed (PS) emerge as pivotal parameters, with optimal outcomes observed at 250 °C and 15 mm/s, signifying their paramount importance. In contrast, layer thickness (LT) and raster orientation (RO) exhibit less influence on tribological properties. Furthermore, a notable transformation in surface characteristics is evident, with untreated TPU presenting a smoother profile than treated TPU.This research underscores the potential of deep cryogenic treatment to augment the tribological and mechanical properties of TPU, rendering it a compelling prospect for orthopedic implants. These findings contribute significantly to the ongoing endeavor to enhance implant materials and their durability in biomedical applications.

Molecular simulation investigations on the interaction properties of graphene oxide-reinforced polyurethane nanocomposite toward the improvement of mechanical properties

Thermoplastic polyurethanes (TPU) exhibit as multipurpose materials with diverse industrial applications. Meanwhile, owing to the brittleness and aging properties of neat TPU which severely limits its applications, the nanofillers were incorporated into the matrix to improve its physical properties. This can be attributed to the enriched interfacial interactions between the TPU moiety and the vastly reactive nanofiller hence the interpretation of interaction properties of the host-guest complex is highly constructive. Quantum mechanics-based molecular simulations was used to evaluate the structural, energetic, interaction nature, and mechanical properties of reinforced graphene oxide (GO) as potent nanofiller in the TPU matrix. Density functional theory-based calculations showed that TPU exhibited strong interaction with GO functional groups at the edge and on the surface, with interaction energies of − 35.303 and − 39.098 kcal/mol, respectively. The atominmolecule analysis indicated the existence of numerous hydrogen bonds between the GO nanofiller and TPU matrix in the nanocomposite. Reactive molecular dynamics simulations are used in the present study for the first time to examine the structural and mechanical properties of the TPU matrix and TPU/GO nanocomposite. Accuracy of reactive forcefield ReaxFF for physical and mechanical property estimations are validated against the reported experiments for the graphene system. It was found that the incorporation of GO (18 wt%) resulted in an increased Young’s modulus by about 34% (from 281 GPa for TPU to 378 GPa for TPU/GO). The charge analysis using the ReaxFF approach showed a significant charge transfer (3.483 e) from the TPU matrix to the GO skeleton. All these reveal the strong binding of GO to the TPU molecular chain in the nanocomposite, improving its physical and mechanical properties. Our comprehensive molecular simulations provide a well-grounded understanding of the interfacial interactions and mechanical properties of the nanofiller-reinforced polymer matrix. The present implemented computational methods and obtained results provide helpful information for the design and improvement of TPU/Graphene-based nanocomposites for potential applications in a new class of environmentally friendly shape memory materials.

Impediment effect of two-dimensional graphene on gaseous fluorine permeation during direct fluorination of polyurethane

Direct fluorination with gaseous fluorine (F2) is a simple way to prepare fluorine-containing polymers, however, partial hydrolysis of CONH- group during fluorination process often reduces the bulk properties of fluorinated polyurethane (PU). Here, two-dimensional graphene (GE) as barrier layer was introduced into the thermoplastic polyurethane (TPU) matrix followed by fluorination treatment by F2 gas. The conjugated π structure of graphene limited excessive fluoridation of the GE/TPU sample, while the large aspect ratio restrained the diffusion and penetration of F2 gas in the bulk. As a result, rich F elements were accumulated on the surface with the slightly-fluorinated bulk. The fluorinated GE/TPU sample integrated the excellent mechanical properties of TPU with friction behaviors of fluorine-containing polymers. The initial friction coefficient was 0.5, 50% lower than the original GE/TPU while maintaining the unchanged mechanical modulus and thermal stability. This research may effectively solve the issue on performance degradation caused by partial hydrolysis of polymer materials containing CONH- group during fluorination process, providing a simple and effective surface modification strategy for preparing high-performance fluorine-containing TPU.

Three-dimensional printed thermoplastic polyurethane on fabric as wearable smart sensors

The microstrip patch antenna (MPA) with a thermoplastic substrate has been widely used in wearable sensors primarily due to its lightweight, flexibility, strength, and compactness. But up till now, little has been conveyed on the use of three-dimensional (3D) printed thermoplastic polyurethane (TPU) on cotton-lycra woven (CLW) fabric-based substrate as a wearable sensor. This study presents a novel and scalable approach for characterizing, simulating, and fabricating the substrate for wearable sensor applications. In this study 3D printing of TPU on CLW fabric (70% cotton (on the warp side)-30% lycra (on the weft side) using fused filament fabrication (FFF) process) has been reported with a tradeoff between flexibility and strength (of a substrate for wearable sensor applications). The rheological, mechanical, morphological, four-dimensional (4D), and resonance frequency (RF) characterization of the substrate has been established. As regards rheological properties, the melt flow index (MFI) of primary (1°) recycled TPU was observed as 29.758 g/(10min). Further, the optimized 3D printing settings of TPU were obtained based on the mechanical testing (minimum stiffness, maximum peak strength (PS), maximum Young's modulus (E), and maximum strain energy (SE)) which comes out to be 225°C nozzle temperature, 18 mm/s printing speed and 60% infill density with a stiffness of 3.311 N/mm and PS of 9.628 MPa. The mechanical properties of TPU printed on stretched and unstretched CLW fabric were tested for lower stiffness (more flexibility). To ascertain the mechanical properties, porosity analyses of samples printed on CLW fabric have been performed based on scanning electron microscopy (SEM). For dielectric properties, and RF characterization, the ring resonator (RR) test was performed based on a Vector network analyzer (VNA). Finally, 4D characterization of the substrate was performed by applying a load from 0 to 25 N, resulting in programable RF output (in the industry scientific and medicine (ISM) band).

Improving the Reaction-to-Fire Properties of Thermoplastic Polyurethane by New Phosphazene-Triazinyl-Based Covalent Organic Framework.

In this study, an approach to simultaneously improve fire resistance and mechanical performance of thermoplastic polyurethane (TPU) was introduced through the penetration of a conjugated network containing nitrogen and phosphorus elements. For this purpose, a Bg-HCCP COF was synthesized through a solvothermal method from benzoguanamine (Bg) and hexachlorophosphazene (HCCP) monomers. Then, it was combined with TPU using the wet mixing method. The TPU/Bg-HCCP composites showed better mechanical strength than the untreated sample. The fire safety of TPU/Bg-HCCP composites was greatly improved by increasing the Bg-HCCP contents. The reduction of the peak heat release rate and the total heat release for the TPU/Bg-HCCP composite with 3 wt % Bg-HCCP were about 44.8 and 60.4%, respectively. Besides, the results showed that adding Bg-HCCP to TPU significantly improved the suppression of smoke generation so that 3% by weight of the fire retardant reduced the total smoke released by 53.1%. It also decreased the peak of the carbon monoxide production rate by 26.5%. Generally, our research provides a promising strategy for constructing flame-retardant composites with high performance.

Nanohybrid of Co3O4 Nanoparticles and Polyphosphazene-Decorated Ultra-Thin Boron Nitride Nanosheets for Simultaneous Enhancement in Fire Safety and Smoke Suppression of Thermoplastic Polyurethane.

Thermoplastic polyurethane (TPU) is widely used in daily life due to its characteristics of light weight, high impact strength, and compression resistance. However, TPU products are extremely flammable and will generate toxic fumes under fire attack, threatening human life and safety. In this article, a nanohybrid flame retardant was designed for the fire safety of TPU. Herein, Co3O4 was anchored on the surface of exfoliated ultra-thin boron nitride nanosheets (BNNO@Co3O4) via coprecipitation and subsequent calcination. Then, a polyphosphazene (PPZ) layer was coated onto BNNO@Co3O4 by high temperature polymerization to generate a nanohybrid flame retardant named BNNO@Co3O4@PPZ. The cone calorimeter results exhibited that the heat release and smoke production during TPU combustion were remarkably restrained after the incorporation of the nanohybrid flame retardant. Compared with pure TPU, the peak heat release rate (PHRR) decreased by 44.1%, the peak smoke production rate (PSPR) decreased by 51.2%, and the peak CO production rate (PCOPR) decreased by 72.5%. Based on the analysis of carbon residues after combustion, the significant improvement in fire resistance of TPU by BNNO@Co3O4@PPZ was attributed to the combination of quenching effect, catalytic carbonization effect, and barrier effect. In addition, the intrinsic mechanical properties of TPU were well maintained due to the existence of the PPZ organic layer.

A robust metal-organic framework nanofibrous membrane as filter for fast separation of cationic dyes from aqueous solution

• Bio-MOF-1@TPU NFM with robust mechanical properties was successfully fabricated. • Bio-MOF-1@TPU NFM can be used as a filter to separate cationic dye from aqueous solution. • Bio-MOF-1@TPU NFM exhibited fast filtration ability and stable reuse effect. • The separation process was based on the ion-exchange and monolayer adsorption mechanisms. A robust metal-organic framework (MOF) nanofibrous membrane (NFM) was successfully fabricated via electrospinning by employing thermoplastic polyurethane (TPU) as substrate and encapsulating anionic bio-MOF-1 into TPU nanofibers. Characterization with FT-IR, EDS and PXRD confirmed that the crystal structure of bio-MOF-1 maintained well in TPU nanofibers. Based on the ion-exchange mechanism, the as-prepared bio-MOF-1@TPU NFM can be used as a filter for efficient separation of cationic dyes from mixed dyes aqueous solution. Benefiting from the robust mechanical properties of TPU, the bio-MOF-1@TPU NFM can repeatedly withstand the suction filtration pressure without damage, resulting in a very fast dye separation process that completed within 70 s, and a very stable reuse effect that the removal efficiency of MB + was just 9.0 % less than that of the first filtration after five cycles of use. This work will be useful for the design of MOFs NFMs based on electrospinning applied to fast separating organic dyes from practical wastewater.

Interface assembly of flower-like Ni-MOF functional MXene towards the fire safety of thermoplastic polyurethanes

In this study, three-dimensional flower-like Ni-MOFs were fabricated and successfully functionalized on multi-terminal lamellar MXene (Ti3C2Tx) by solvothermal method, and their flame retardant application in thermoplastic polyurethanes (TPU) was investigated. As expected, the addition of Ni-MOF@Ti3C2Tx can improve the flame retardancy and smoke suppression properties of TPU. The heat release rate, the smoke release rate, total smoke production, CO and CO2 release of the composite with only 1 wt% MOF@Ti3C2Tx were significantly reduced by 15%, 44%, 26%, 18%, and 8%, respectively. Furthermore, the carbon residues of TPU/Ni-MOF@Ti3C2Tx composites were about 2–5 times that of pure TPU, indicating that the Ni-MOF@Ti3C2Tx can inhibit the thermal degradation of TPU. The mechanism illustrated that the excellent fire safety properties of TPU/Ni-MOF@Ti3C2Tx composites are due to the physical barrier, catalytical carbonization, and gas-phase flame retardant of Ni-MOF@Ti3C2Tx. In this work, the dispersity, thermal stability, and flame retardancy of MXene were improved due to the modification of MXene with Ni-MOF by chemical bonding and physical adsorption, which can broaden the range of applications of MOFs.

Preparation of Ni-Fe layered double hydroxides and its application in thermoplastic polyurethane with flame retardancy and smoke suppression

Aluminum hypophosphite (AHP), as an effective phosphorus-based flame retardant used in thermoplastic polyurethane (TPU), released a large amount of smoke and toxic gasses during combustion. In this work, a flame retardant filler, Ni-Fe layered double hydroxides (NiFe-LDHs), was synthesized and applied in TPU together with AHP. The limiting oxygen index (LOI) of the TPU/6AHP/1NiFe-LDH composite reached 30.7% with a V-0 rating in the UL-94 test. Compared with neat TPU, the peak heat release rate (pHRR) and total heat release (THR) values of TPU/6AHP/1NiFe-LDH sample were reduced by 67.9% and 40.8%, respectively. Moreover, both the smoke production and CO/CO2 yield were also decreased sharply. It was proposed that NiFe-LDH provided the effect of catalyzing char formation, and the obtained dense char layer was able to block both heat and smoke release. In addition, the addition of NiFe-LDH had little effect on the mechanical properties of TPU, and the tensile strength and elongation at break only decreased by 6.0% and 6.9%, respectively. This work provides a new strategy for fillers and flame retardants to improve the flame retardant properties and smoke suppression of TPU.

Synergistic thermodynamic compatibility of polydimethylsiloxane block in thermoplastic polyurethane for flame retardant materials: Super flexible, highly flame retardant and low smoke release

A method of mixing soft segments was used to solve the thermodynamic incompatibility problem, which provided direction for the synthesis of better-performing silicone-modified thermoplastic polyurethane (TPU). The polytetrahydrofurandiol (PTMG) based TPU blocked by hydroxybutane terminated polydimethylsiloxane (PDMS) was synthesized by the bulk polymerization. Using FTIR fitting, WAXR, DSC and DMA to explore the effect of PDMS on the microstructure of TPU, mechanical tests, TGA, static contact angle and flame retardant tests were used to test the macroscopic properties of TPUs. The results showed that: PDMS had a remodeling effect on the formation of TPU microstructure, which made the fine three-phase structure formed in Si-TPU. PDMS had the effect of increasing elongation at break for TPU, increasing the elongation at break by 173.8%. PDMS reduced the decomposition rate and increased the hydrophobicity with a water contact angle to 111.5°. Moreover, the TPU modified with silicone had good flame retardancy, with the limiting oxygen index (LOI) reaching 27, which reduced the total heat release to less than half of the original and inhibited smoke release. The non-polar and non-hydrogen bonding hydroxybutane terminated polydimethylsiloxane (PDMS) was introduced as a modifier into polytetrahydrofuran diol (PTMG)-based thermoplastic polyurethane (TPU). The effect of PDMS on the microstructure of PTMG-based TPU with strong hydrogen bonding was explored, which also had an impact on the macroscopic properties. • The method of mixing soft segments is used to solve the larger thermodynamic incompatibility between hydroxybutane terminated polydimethylsiloxane (PDMS) and thermoplastic polyurethane (TPU). • PDMS could produce a finer three-phase structure in TPU, and the degree of crystallinity and microphase mixing decrease with the increase of PDMS. • The addition of PDMS produces a linear decrease in the mechanical properties of TPU but improves the hydrophobicity and flame retardancy.

TPU/CNTs flexible strain sensor with auxetic structure via a novel hybrid manufacturing process of fused deposition modeling 3D printing and ultrasonic cavitation-enabled treatment

The broad technological concept as so-called "hybrid additive manufacturing" is introduced into the fabrication of flexible strain sensing structure, employing the combination process of fused deposition modeling (FDM) 3D printing technique and ultrasonic cavitation-enabled treatment. We customize the FDM settings to print auxetic structures with a negative Poisson's ratio (NPR), using the flexible thermoplastic polyurethane (TPU) material. Then, we employ the ultrasonic cavitation-enabled treatment conducted towards the flexible auxetic structure immersing in carbon nanotubes (CNTs) liquid, aiming to embed the CNTs into the surface layer of the auxetic structures. It is equivalent to two additive manufacturing steps, proving effective in designing and fabricating flexible strain sensors. Instead of 3D printing after the hybridization of the TPU matrix material, this manufacturing procedure can ensure that the intrinsic excellent mechanical properties of TPU are not weakened due to the internally mixed conductive materials but able to exhibit usable sensing performances. The Poisson's ratio of the sensor structure is - 0.8. The sensor achieves over 300% strain. The sensitivity within the initial strain range is 2.661. The reliability of signal acquisition during the cyclic deformations is proved. Its response-recovery duration under 5% strain at 500 mm/min deformation rate is 130 ms(response)− 250 ms(recovery). It gives accurate feedback to external stimuli at different frequencies. It can maintain stable output signals during 3000 cycles of stretching. It also can sense 1% minor-strain stimuli. The strain sensing behavior of the fabricated flexible sensor with the auxetic structure is detailed. The CNTs are combined tightly with the TPU surface layer to form a conductive network with variable resistance during recoverable deformation of the auxetic structure. The macro and micro-mechanisms of sensing are dissected, considering the tunneling effect of discontinuous CNTs. The hybrid additive manufacturing process is verified to be feasible, credible, and low-cost for easy fabrication of flexible strain sensors with complex geometry configurations.

Multi-physics properties of thermoplastic polyurethane at various fused filament fabrication parameters

PurposeThe purpose of this study is to test a flexible polymer with different characteristics compared to other classical polymers mostly used in the additive manufacturing process, and to improve its mechanical properties and microstructure, by modifying different printing parameters, to make it more suitable for various industrial applications.Design/methodology/approachSeven parameters were tested, namely, nozzle temperature, bed temperature, layer thickness, printing speed, flow rate, printing time gap between two successive printed layers and raster orientation. Rheological characterizations were conducted to evaluate the influence of nozzle temperature on the melt viscosity of thermoplastic polyurethane (TPU). The effect of thermal printing parameters on the crystallinity behavior was explored. Tomographic characterizations were realized to measure the porosity and evaluate the internal structure quality of printed specimens.FindingsIncreases of the nozzle temperature, bed temperature, layer thickness and flow rate had a positive influence on the tensile strength properties of TPU with a reduction of porosity. Higher printing speeds created defects and negatively influenced the strength properties of TPU. An increase in the printing time gap between layers led to poor interlayer adhesion and decreased the tensile strength. Specimens with layers all oriented parallel to the loading direction exhibited superior mechanical properties compared to other raster orientations.Originality/valueThermoplastic elastomers are a unique class of polymers characterized by the combined thermal, chemical and mechanical properties of their elastomer and thermoplastic parts. TPU elastomer, as one of the elastomer families, has found an important position in the bioengineering and three-dimensional printing industry. This study reports a comprehensive study of the impact of additive manufacturing parameters on the properties of TPU.