On the Synergistic Effect of Multi-Walled Carbon Nanotubes and Graphene Nanoplatelets to Enhance the Functional Properties of SLS 3D-Printed Elastomeric Structures

Elastomer-based porous structures realized by selective laser sintering (SLS) are emerging as a new class of attractive multifunctional materials. Herein, a thermoplastic polyurethane (TPU) powder for SLS was modified by 1 wt.% multi-walled carbon nanotube (MWCNTs) or a mixture of MWCNTs and graphene (GE) nanoparticles (70/30 wt/wt) in order to investigate on both the synergistic effect provided by the two conductive nanostructured carbonaceous fillers and the correlation between formulation, morphology, and final properties of SLS printed porous structures. In detail, porous structures with a porosity ranging from 20% to 60% were designed using Diamond (D) and Gyroid (G) unit cells. Results showed that the carbonaceous fillers improve the thermal stability of the elastomeric matrix. Furthermore, the TPU/1 wt.% MWCNTs-GE-based porous structures exhibit excellent electrical conductivity and mechanical strength. In particular, all porous structures exhibit a robust negative piezoresistive behavior, as demonstrated from the gauge factor (GF) values that reach values of about −13 at 8% strain. Furthermore, the G20 porous structures (20% of porosity) exhibit microwave absorption coefficients ranging from 0.70 to 0.91 in the 12–18 GHz region and close to 1 at THz frequencies (300 GHz–1 THz). Results show that the simultaneous presence of MWCNTs and GE brings a significant enhancement of specific functional properties of the porous structures, which are proposed as potential actuators with relevant electro-magnetic interference (EMI) shielding properties.

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

Applied Sciences ◽

10.3390/app9050864 ◽

2019 ◽

Vol 9 (5) ◽

pp. 864 ◽

Cited By ~ 12

Author(s):

Alfredo Ronca ◽

Gennaro Rollo ◽

Pierfrancesco Cerruti ◽

Guoxia Fei ◽

Xinpeng Gan ◽

...

Keyword(s):

Thermoplastic Polyurethane ◽

Selective Laser Sintering ◽

Three Dimensional ◽

Laser Sintering ◽

Gauge Factor ◽

Strain Sensitivity ◽

Porous Structures ◽

Compression Tests ◽

Triply Periodic ◽

Unit Cells

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.

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Fabrication of Piezo-Resistance Composites Containing Thermoplastic Polyurethane/Hybrid Filler Using 3D Printing

Sensors ◽

10.3390/s21206813 ◽

2021 ◽

Vol 21 (20) ◽

pp. 6813

Author(s):

Kyoungho Song ◽

Hansol Son ◽

Suwon Park ◽

Jonghan Lee ◽

Jungsik Jang ◽

...

Keyword(s):

Thermoplastic Polyurethane ◽

Pressure Sensors ◽

Strain Range ◽

Electrical Network ◽

Gauge Factor ◽

Hybrid Filler ◽

Hybrid Fillers ◽

Potential Applications ◽

Multi Walled Carbon Nanotubes ◽

Piezoresistive Pressure Sensors

In this study, 3D-printable flexible piezoresistive composites containing various amounts of cilia-like hybrid fillers were developed. In the hybrid fillers, micro-scale Cu particles with a 0D structure may allow them to easily disperse into the flexible TPU matrix. Furthermore, nanoscale multi-walled carbon nanotubes (MWCNTs) with a high aspect ratio, present on the surface of the Cu particles, form an electrical network when the polymer matrix is strained, thus providing good piezoresistive performance as well as good flowability of the composite materials. With an optimal hybrid filler content (17.5 vol.%), the 3D-printed piezoresistive composite exhibits a gauge factor of 6.04, strain range of over 20%, and durability of over 100 cycles. These results highlight the potential applications of piezoresistive pressure sensors for health monitoring, touch sensors, and electronic skin.

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Effect of pre-strain and KMnO4 oxidation of carbon nanotubes embedded in polyurethane on strain dependent electrical resistance of the composite

Sensor Review ◽

10.1108/sr-05-2017-0079 ◽

2018 ◽

Vol 38 (2) ◽

pp. 163-170 ◽

Cited By ~ 1

Author(s):

Petr Slobodian ◽

Pavel Riha ◽

Robert Olejnik ◽

Jiri Matyas

Keyword(s):

Carbon Nanotubes ◽

Synergistic Effect ◽

Electrical Resistance ◽

Tensile Deformation ◽

Gauge Factor ◽

Content Type ◽

Polyurethane Composite ◽

Multi Walled Carbon Nanotubes ◽

Kmno4 Oxidation ◽

Strain Dependent

Purpose The synergistic effect of functionalization of multi-walled carbon nanotubes (CNT) using KMnO4 oxidation and initial tensile deformation on the electrical resistance of nanotube network/polyurethane composite subjected to elongation was studied. Design/methodology/approach Though the initial deformation irreversibly changed the arrangement of carbon nanotube network, subsequent cyclic elongation confirmed stable resistance values. The increased strain-dependent resistance of stimulated nanotube network/polyurethane composite was demonstrated by monitoring vibration of tambour leather after a bead impact and finger flexion. Findings The results showed a tenfold composite resistance increase for the composite prepared from KMnO4 oxidized nanotubes, quantified by a so-called gauge factor, from a value of about 20 in comparison to the network prepared from pristine nanotubes. This is a substantial increase, which ranks the stimulated composite among materials with the highest electromechanical response. Originality/value The results in this paper are new and have not been published yet. The paper combines different ideas which are developed together. It presents a new concept of synergistic effect of CNT oxidation and application of pre-strain simulation. Oxidation and pre-strain increases by several times the sensitivity of the tested composites which are predetermined for use as strain sensors of various sizes and shapes.

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Temperature-Dependent Synergistic Effect of Multi-Walled Carbon Nanotubes and Graphene Nanoplatelets on the Tensile Quasi-Static and Fatigue Properties of Epoxy Nanocomposites

Polymers ◽

10.3390/polym13010084 ◽

2020 ◽

Vol 13 (1) ◽

pp. 84

Author(s):

Yi-Ming Jen ◽

Hao-Huai Chang ◽

Chien-Min Lu ◽

Shin-Yu Liang

Keyword(s):

Carbon Nanotubes ◽

Fatigue Strength ◽

Synergistic Effect ◽

Polymer Nanocomposites ◽

Graphene Nanoplatelets ◽

Temperature Dependent ◽

Epoxy Nanocomposites ◽

Hybrid Fillers ◽

Multi Walled Carbon Nanotubes ◽

Walled Carbon Nanotubes

Even though the characteristics of polymer materials are sensitive to temperature, the mechanical properties of polymer nanocomposites have rarely been studied before, especially for the fatigue behavior of hybrid polymer nanocomposites. Hence, the tensile quasi-static and fatigue tests for the epoxy nanocomposites reinforced with multi-walled carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) were performed at different temperatures in the study to investigate the temperature-dependent synergistic effect of hybrid nano-fillers on the studied properties. The temperature and the filler ratio were the main variables considered in the experimental program. A synergistic index was employed to quantify and evaluate the synergistic effect of hybrid fillers on the studied properties. Experimental results show that both the monotonic and fatigue strength decrease with increasing temperature significantly. The nanocomposites with a MWCNT (multi-walled CNT): GNP ratio of 9:1 display higher monotonic modulus/strength and fatigue strength than those with other filler ratios. The tensile strengths of the nanocomposite specimens with a MWCNT:GNP ratio of 9:1 are 10.0, 5.5, 12.9, 23.4, and 58.9% higher than those of neat epoxy at −28, 2, 22, 52, and 82 °C, respectively. The endurance limits of the nanocomposites with this specific filler ratio are increased by 7.7, 26.7, 5.6, 30.6, and 42.4% from those of pristine epoxy under the identical temperature conditions, respectively. Furthermore, the synergistic effect for this optimal nanocomposite increases with temperature. The CNTs bridge the adjacent GNPs to constitute the 3-D network of nano-filler and prevent the agglomeration of GNPs, further improve the studied strength. Observing the fracture surfaces reveals that crack deflect effect and the bridging effect of nano-fillers are the main reinforcement mechanisms to improve the studied properties. The pullout of nano-fillers from polymer matrix at high temperatures reduces the monotonic and fatigue strengths. However, high temperature is beneficial to the synergistic effect of hybrid fillers because the nano-fillers dispersed in the softened matrix are easy to align toward the directions favorable to load transfer.

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Investigation of Structure-Property Relationships in Thermoplastic Polyurethane/Multiwalled Carbon Nanotube Composites

Volume 2: Additive Manufacturing; Materials ◽

10.1115/msec2017-2760 ◽

2017 ◽

Cited By ~ 1

Author(s):

Felicia Stan ◽

Catalin Fetecau ◽

Nicoleta V. Stanciu ◽

Razvan T. Rosculet ◽

Laurentiu I. Sandu

Keyword(s):

Electrical Properties ◽

Shear Viscosity ◽

Thermoplastic Polyurethane ◽

Structure Property ◽

Multiwalled Carbon ◽

Structure Property Relationships ◽

Mechanical And Electrical Properties ◽

High Shear Rates ◽

Nanotube Composites ◽

Multi Walled Carbon Nanotubes

In this study, the structure-property relationships in thermoplastic polyurethane (TPU) filled with multi-walled carbon nanotubes (MWCNTs) were investigated. Firstly, the contribution of MWCNTs to the melt shear viscosity and the pressure-volume-temperature (pVT) behavior was investigated. Secondly, injection-molded samples and 2 mm diameter filaments of TPU/MWCNT composites were fabricated and their mechanical and electrical properties analyzed. It was found that the melt processability of TPU/MWCNT composites is not affected by the addition of a small amount (1–5 wt.%) of MWCNTs, all composites displaying shear-thinning at high shear rates. The mechanical and electrical properties of the TPU/MWCNT composites were substantially enhanced with the addition of MWCNTs. However, the conductivity values of composites processed by injection molding were two and three orders of magnitude lower than those of composites processed by extrusion, highlighting the role of melt shear viscosity on the dispersion and agglomeration of nanotubes.

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EXPERIMENTAL INVESTIGATION AND SIMULATION OF 3D-PRINTED LATTICE STRUCTURES

Acta Polytechnica CTU Proceedings ◽

10.14311/app.2019.25.0052 ◽

2019 ◽

Vol 25 ◽

pp. 52-57

Author(s):

Eva Heiml ◽

Anna Kalteis ◽

Zoltan Major

Keyword(s):

Mechanical Performance ◽

Bulk Material ◽

Deformation Behaviour ◽

Lightweight Design ◽

Thermoplastic Polyurethane ◽

Selective Laser Sintering ◽

Structural Performance ◽

Lattice Structures ◽

3D Printed ◽

Manufacturing Techniques

Lattice structures are currently of high interest, especially for lightweight design. They generally have better structural performance per weight than parts made of bulk material. With conventional manufacturing techniques they are diﬃcult to produce, but with additive manufacturing (AM) fabricationisfeasible. To better understand their behaviour under various loading conditions two lattice structures in diﬀerent conﬁgurations were observed. For each structure three diﬀerent test specimens were designed and manufactured using selective laser sintering (SLS). To investigate the mechanical performance under large deformations the specimens were made of a thermoplastic polyurethane(TPU), which shows a hyperelastic material behaviour. Beside the experimental observations also ﬁnite element analyses (FEA) were conducted to investigate the deformation behaviour in more detail.

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Fabrication of Multilayered Polymer Composite Fibers for Enhanced Functionalities

Volume 2: Manufacturing Processes; Manufacturing Systems; Nano/Micro/Meso Manufacturing; Quality and Reliability ◽

10.1115/msec2021-64039 ◽

2021 ◽

Author(s):

Weiheng Xu ◽

Dharneedar Ravichandran ◽

Sayli Jambhulkar ◽

Yuxiang Zhu ◽

Kenan Song

Keyword(s):

Mechanical Stability ◽

Thermoplastic Polyurethane ◽

Hot Isostatic Pressing ◽

Air Pressure ◽

Gauge Factor ◽

Piezoresistive Sensor ◽

Macro Scale ◽

Facile Fabrication ◽

Surface Morphologies ◽

Hierarchal Structure

Abstract Carbon nanoparticles-based polymer composites have wide applications across different fields for their unique functional properties, durability, and chemical stability. When combining nanoparticle morphologies with micro- or macro-scale morphologies, the hierarchal structure often would greatly enhance the composites’ functionalities. Here in this work, a thermoplastic polyurethane (TPU) and graphene nanoplatelets (GnPs) based multilayered fiber is fabricated through the combination of dry-jet-wet spinning, based on an in-house designed spinneret which accommodates three layers spinning solution, and hot isostatic pressing (HIP), at 220 °C. The multilayered spinneret enables the spinnability of a high GnPs loaded spinning dope, highly elastic, with great mechanical strength, elongation, and flexibility. The HIP process resulted in superior electrical properties as well as a newly emerged fourth hollow layer. Together, such a scalable fabrication method promotes a piezoresistive sensor that is sensitive to uniaxial strain and radial air pressure. The hollow fiber is characterized based on surface morphologies, layer formation, percolation threshold, piezoresistive gauge factor, mechanical stability and reversibility, and air-pressure sensitivity and reversibility. Such facile fabrication methods and unique structures have combined the mechanically robust outer shell with a highly conductive middle sensing layer for a new sensor with great potentials in wearable, robotics, biomedical, and other areas.

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