Improved electrical conductivity of TPU/carbon black composites by addition of COPA and selective localization of carbon black at the interface of sea-island structured polymer blends

Study on CNT/TPU cube under the 3D printing conditions of infill patterns and density

In this study, to develop soft pressure sensor applicable to wearable robots using stretchable polymers and conductive fillers, 3.25 wt% carbon nanotubes/thermoplastic polyurethane filament with shore 94 A were manufactured. Three infill densities (20%, 50%, and 80%) and patterns (zigzag (ZG), triangle (TR), honeycomb (HN)) were applied to print cubes via fused filament fabrication 3D printing. Most suitable infill conditions were confirmed based on the slicing images, morphologies, compressive properties, electrical properties, and electrical heating properties. For each infill pattern, ZG and TR divided the layers into lines and figures, and the layers were stacked by rotation. For HN, the same layers were stacked in a hexagonal pattern. Consequently, TR divided layer in various directions, showed the strongest compressive properties with toughness 1.99 J for of infill density 80%. Especially, the HN became tougher with increased infill density. Also, the HN laminated with the same layer showed excellent electrical properties, with results greater than 14.7 mA. The electrical heating properties confirmed that ZG and HN had the high layer density, which exhibited excellent heating characteristics. Therefore, it was confirmed that performance varies depending on the 3D printing direction, and it was confirmed that HN is suitable for manufacturing soft sensors.

Electrical Heaters for Anti/De-Icing of Polymer Structures

The problem of icing for surfaces of engineering structures requires attention more and more every year. Active industrialization in permafrost zones is currently underway; marine transport in Arctic areas targets new goals; the requirements for aerodynamically critical surfaces of wind generators and aerospace products, serving at low temperatures, are increasing; and fiber-reinforced polymer composites find wide applicability in these structural applications demanding the problem of anti/de-icing to be addressed. The traditional manufacturing approaches are superimposed with the new technologies, such as 3D printers and robotics for laying heat wires or cheap and high-performance Thermal Sprayed methods for metallic cover manufacturing. Another next step in developing heaters for polymer structures is nano and micro additives to create electrically conductive heating networks within. In our study, we review and comparatively analyze the modern technologies of structure heating, based on resistive heating composites.

A highly stretchable and ultra-sensitive strain sensing fiber based on a porous core-network sheath configuration for wearable human motion detection

Functional fibers have attracted much research attention due to their potential application in developing advanced electronic textiles for wearable devices. However, challenges still exist in preparing high-performance fiber-shaped sensors with superior flexibility and stretchability while achieving a high sensitivity and a wide detection range. Herein, we propose the design and fabrication of an ultra-flexible and super-elastic fiber-shaped strain sensor via a facile combining approach of wet-spinning and dip-coating. The sensor adopts a core-sheath configuration of liquid metal droplets dispersed in porous thermoplastic polyurethane as a substrate core and a carbon nanotube intertwined network embedding silver nanowires as a strain sensitive sheath. By taking advantage of both the composition of multiple functional materials and the design of a microstructured device configuration, the developed fiber-shaped sensor exhibits an ultrahigh sensitivity (maximum gauge factor of 7336.1), an extremely large workable strain range (500%), a low strain detection limit (0.5%), a fast response time (200 ms) and good stability (10 000 cycles). In addition, the sensor is temperature insensitive, inert under harsh solution conditions, degradable and recyclable. Intriguingly, the fiber-shaped sensor can be used to detect various human motions and gestures by directly attaching to skins or elaborately weaving into textiles, demonstrating its great potential in human healthcare monitoring and human-machine interactions.

Ultrathin Stretchable Triboelectric Nanogenerators Improved by Postcharging Electrode Material

Sustainable ultrathin stretchable power sources have emerged with the development of wearable electronics. They obtain energy from living organisms and the environment to drive these wearable electronics. Here, an ultrathin stretchable and triboelectric nanogenerator (TENG) improved by chargeable carbon black (CB)/thermoplastic polyurethane (TPU) composite material (CT-TENG) is proposed for mechanical energy harvesting and physiological signal sensing. The CB/TPU composite can act as both a stretchable electrode and a triboelectric layer due to the coexistence of conductive CB and dielectric TPU. The CT-TENG demonstrates good stretchability (≈646%), ultrathin thickness (≈50 μm), and a lightweight (≈62 mg). The triboelectric electrode material can be improved by postcharging treatment. With the corona charging process, the output performance of the CT-TENG was improved eightfold and reached 41 V. Moreover, the CT-TENG with a self-powered sensing capability can inspect the amplitude and frequency of different physiological movements. Consequently, the CT-TENG is promising in promoting the development of electronic skins, wearable systems of self-powered sensors, human-machine interactions, soft robotics, and artificial intelligence applications.

Comparison of Three Interfacial Conductive Networks Formed in Carbon Black-Filled PA6/PBT Blends

Interfacial localization of carbon fillers in cocontinuous-structured polymer blends is well-known as a high-efficiency strategy for conductive network formation. However, a comparison with interfacial localization of carbon fillers in sea-island-structured polymer blends is lacking. Here, three types of highly efficient conductive networks formed on the basis of interfacial localization of carbon black (CB) in polyamide 6 (PA6)/poly(butylene terephthalate) (PBT) blends with different blend compositions (80/20, 50/50 and 20/80 vol/vol) were investigated and compared in terms of electrical resistivity, morphology as well as rheological and mechanical properties. The order of the electrical percolation threshold of CB in the three blends is 50/50 < 20/80 < 80/20, which can be attributed to different network structures. The rheological percolation thresholds are close to the electrical ones, confirming the formation of CB networks. The formation mechanisms for the three types of CB network structures are analyzed. All the three types of PA6/PBT-6 vol% CB composites showed improved tensile strength compared with PA6/PBT blends, being in favor for practical applications.

Distinctive Morphology Modifiers for Polymer Blends: Roles of Asymmetric Janus Nanoparticles during Phase Separation

Janus nanoparticles (JPs), which are anisotropic nanoparticles with multiple constituting parts, have been recognized as superior compatibilizers for polymer-blend-based nanocomposites. However, so far, most studies focused on the effects of symmetric JPs on the phase separation dynamics of polymer blends, while the roles of asymmetric JPs during phase separation remain unclear. In this work, the phase separation dynamics of symmetric blends compatibilized by JPs with various compositions was studied by using dissipative particle dynamics (DPD) simulations. It was found that the blends compatibilized by asymmetric JPs tend to undergo morphological transitions from bicontinuous networks to droplets-in-matrix structures at the late stage of phase separation, which is due to the influence of asymmetric JPs on the energetically favored curvature of the interfaces between polymer domains. Such a mechanism is absent for symmetric JPs and other compatibilizers (e.g., triblock copolymers and homogeneous particles) because they lack the unique combination of chemical asymmetry with the particulate nature like the asymmetric JPs. Moreover, it was observed that the asymmetric JPs can stably localize at the interfaces and act as efficient compatibilizers only when the fraction of the minor constituent part exceeds a critical value. These findings not only shed light upon the roles of asymmetric JPs as compatibilizers but also indicate a promising strategy for designing polymer-blend-based nanocomposites with tailor-made structures.

Effect of Carbon Black Nanofiller on Adhesion Properties of SBS Rubber Surfaces Treated by Low-Pressure Plasma

Studies on the surface modification of commercial styrene-butadiene-styrene (SBS) rubber with different carbon black (CB) nanofiller content (10–80 parts per hundred parts of rubber (phr)) performed by low-pressure oxygen plasma are presented in this paper. The adhesion properties of the rubber were determined by the peel test for adhesive-bonded joints prepared with a water-based polyurethane (PU) adhesive. The chemical structure and morphology of the SBS rubber surface before and after plasma treatment were investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), respectively. The peel tests showed that the plasma treatment significantly improved the strength of adhesive-bonded joints in the entire range of CB tested, revealing a clear maximum for approximately 50 phr of CB. It was also found that as a result of plasma treatment, functional groups that are responsible for the reactions with the PU adhesive, such as C−OH and C=O, were formed, and their concentration, similar to the peel strength, showed maximum values for approximately 50 phr CB. The occurrence of these maxima was explained using the bound rubber model.

Graphene-Coated Spandex Sensors Embedded into Silicone Sheath for Composites Health Monitoring and Wearable Applications

This study presents a low-cost, tunable, and stretchable sensor fabricated based on spandex (SpX) yarns coated with graphene nanoplatelets (GnP) through a dip-coating process. The SpX/GnP is wrapped into a stretchable silicone rubber (SR) sheath to protect the conductive layer against harsh conditions, which allows for fabricating washable wearable sensors. Dip-coating parameters are optimized to obtain the maximum GnP coating rate. The covering sheath is tailored to achieve high stretchability beyond the sensing limit of 104% for SpX/GnP/SR sensors. Adjustable sensitivity is attained by manipulating SpX immersion times broadening its application for a wide range of strains: Gauge factors as high as two orders of magnitude are achieved at tensile strains greater than ≈40%. The fabricated sensors are tested for two applications: First, the SpX/GnP sensors are integrated into composite fabrics (with no negative impact on the structural integrity of the part) for screening the yarn displacements, resin flow, solidification during the hot press forming process, and structural health monitoring under mechanical loads with minimal cross-sensitivity to temperature/humidity. Second, the capability of SpX/GnP/SP sensors in detection of a wide range of bodily motions (from the joint motion to arterial blood pressure) is demonstrated.

Tunable Electrical Conductivity of Carbon-Black-Filled Ternary Polymer Blends by Constructing a Hierarchical Structure

A type of hierarchical structured composite composed of a minor thermoplastic polyurethane (TPU) phase spreading at the interface of two major phases polyoxymethylene/polyamide copolymer (POM/COPA) and carbon black (CB) particles selectively localized at the TPU/COPA interface of the tri-continuous blends was fabricated by melt compounding. The hierarchical structure was designed according to predictions and verified by a combination of electron microscopy and solvent extraction technique. The hierarchical structured composites show the dramatically decreased percolation threshold, a reduction of 60% compared to those without TPU where CB is selectively distributed in the COPA phase. The effects of CB contents and TPU on the phase morphology of POM/COPA were investigated, showing the occurrence of the POM/COPA phase inversion from a sea-island to a co-continuous structure beyond the percolation threshold of CB in the presence of TPU. The mechanism for the formation of conductive network is construction of CB network at the TPU/COPA interface of tri-continuous POM/COPA/TPU blends and double percolation effect.