Positive/Negative Temperature Coefficient Behaviors of Electron Beam-Irradiated Carbon Blacks-Loaded Polyethylene Nanocomposites

Structural, electrical, and physical-mechanical properties of composites obtained based on filled polyolefins and thermoplastic elastomers

The paper presents the results of a study of the influence of various mineral and metal fillers, as well as carbon black and graphite on the structural features and quality of composite and nanocomposite materials based on polyolefins and their modifications. High density polyethylene (HDPE), low density polyethylene (LDPE), various copolymers of ethylene with α-olefins, polypropylene (PP), polypropylene random copolymer, block copolymer of ethylene with propylene, etc. were used as polyolefins. The filler used was mainly carbon black (CB) and graphite, as well as various natural minerals. The objective of the review material under consideration was to demonstrate promising possibilities for obtaining electrically conductive composite and nanocomposite materials based on dielectric polymers, which are included in the polyolefins. The introduction section examines the state of the problem of development and research of electrically conductive nanocomposites, as well as the goals and objectives of the research. The theoretical aspects of obtaining and studying composite materials based on polyolefins are considered, where the main attention is paid to studying the influence of filler content on the structural features and properties of polymer composites. Particular attention is paid to the compatibility of the mixture components and the establishment of the relationship between the filler particles and the macrochains of the polymer matrix. The significant role of compatibilizers in improving the compatibility of mixture components is shown. The article presents scientific provisions and theoretical background that explain the mechanism of the compatibilization process and its influence on the pattern of changes in electrical conductivity, physical, mechanical, thermophysical and thermal deformation properties of nanocomposites. Much attention is paid to the development of thermoplastic elastomers, taking into account the specifics of the interaction of thermoplastic (polyolefin) macrochains with various synthetic elastomers based on natural, butadiene-nitrile, butadiene-styrene and ethylene-propylene-diene rubbers. The influence of the thermoplastic-elastomer ratio, carbon black and graphite, and their modifications on the structure and properties of nanocomposites based on thermoplastic elastomers is considered. Significant attention is paid to the study of electrical conductivity of nanocomposites based on thermoplastic elastomers. It has been established that the degree of crystallinity of polyolefins and thermoplastic elastomers has a significant effect on the formation of the interspherulitic amorphous region in filled composites, which, in turn, has a primary effect on the mechanism of formation of tunnel and electron conductivity.

Advances in Electrically and Thermally Conductive Functional Nanocomposites Based on Carbon Nanotubes

The paper presents a review of CNTs synthesis methods and their application as a functional filler to obtain polymer composites for various technical purposes for strain gauges, electrical heating, anti-static coatings, electrically conductive compounds, etc. Various synthesis methods allow CNTs with different morphology and structural properties to be created, which expands the possibilities of the application of such nanoscale structures. Polymers can provide such effects as 'shape memory' and self-repair of mechanical defects. Different combinations of polymers and dispersed fillers influence the change in electrical and thermal conductivity, as well as the positive temperature coefficient of resistance, which makes it possible to achieve the effect of temperature self-regulation during electrical heating. CNTs make it possible to form PTCR (positive temperature coefficient of resistance) in elastomers at lower concentrations, which makes it possible to preserve mechanical strength and use more efficient modes of heat generation. For strain gauges, CNTs improve sensitivity to mechanical effects and extend the measurement range. The use of thermoplastic elastomers provides the temperature of PTCR operation for electric heating at the level of 200 °C (voltage 240 V), which allows such heaters to operate at a power supply from a household electrical network. CNTs-based strain gauges can provide structural condition monitoring of composite materials.

Development of Electrically Conductive Wood-Based Panels for Sensor Applications

This study investigates the development of electrically conductive panels for application as emergency detection sensors in smart house systems. These panels, composed of wood chips coated with polymeric methylene diphenyl isocyanate, were modified with carbon black and carbon fibers to enable detection of moisture, temperature, and pressure variations. Manufactured via hot pressing, the panels retained standard mechanical properties and exhibited stable performance under diverse environmental conditions. Carbon black-filled panels achieved electrical percolation at a lower filler concentration (5%) compared to carbon fiber-filled panels. The incorporation of carbon black reduced the electrical resistivity to 8.6 ohm·cm, while the addition of carbon fibers further decreased it to 7.7 ohm·cm. In terms of sensor capabilities, panels containing carbon fibers demonstrated superior sensitivity to moisture and pressure changes. However, carbon black was ineffective for temperature sensing. Among the carbon fiber-filled panels, those with 20 wt.% concentration exhibited the best performance for moisture and pressure detection, whereas panels with 40 wt.% carbon fiber content displayed the most reliable and consistent temperature-sensing properties.

Biphasic GaIn Alloy Constructed Stable Percolation Network in Polymer Composites over Ultrabroad Temperature Region

Flexible and adaptable polymer composites with high-performance reliability over wide temperature range are imperative for various applications. However, the distinct filler-matrix thermomechanical behaviors often cause severe structure damage and performance degradation upon large thermal shock. To address this issue, a general strategy is proposed to construct leakage-free, self-adaptive, stable percolation networks in polymer composites over wide temperature (77-473 K) with biphasic Ga35In65 alloy. The in situ micro-CT technology, for the first time, reveals the conformable phase transitions of Ga35In65 alloys in the polymer matrix that help repair the disruptive conductive networks over large temperature variations. The cryo-expanded Ga compensates the disruptive carbon networks at low temperatures, and flowable Ga and melted In at high temperatures conformably fill and repair the deboned interfaces and yielded crevices. As a proof-of-concept, this temperature-resistant composite demonstrates superb electrical conductivity and electromagnetic interference shielding properties and stability even after a large temperature shock (ΔT = 396 K). Furthermore, the superiority of the construction of temperature self-adaptive networks within the composite enables them for additive manufacturing of application-oriented components. This work offers helpful inspiration for developing high-performance polymer composites for extreme-temperature applications.

Core-Sheath Fiber-Based Triboelectric Nanogenerators for Energy Harvesting and Self-Powered Straight-Arm Sit-Up Sensing

Fiber-based triboelectric nanogenerators (F-TENGs), a green and sustainable energy-harvesting and transformation technology, hold great potential in the areas of portable energy harvesters and smart wearable sensors. Herein, the core-sheath structure F-TENGs (CF-TENGs) are developed by using continuous production equipment. The CF-TENGs, consisting of an elastic conductive fiber (core layer) and silicone rubber (sheath layer), can simultaneously accomplish stable reversible strain and excellent electrical output performance. High outputs (an open-circuit voltage of 17.5 V and a short-circuit current of 0.1 μA at a frequency of 1 Hz) can be attained when the CF-TENGs (a length of 5 cm) are contacted with a nylon fabric. The CF-TENGs not only act as self-powered sensors for applications in motion monitoring but also efficiently transfer mechanical energy into electric energy. As self-powered wearable sensors, the CF-TENGs can accurately indicate various human physiological movements. Moreover, they can be applied on straight-arm sit-up sensing to achieve standardized sport testing. Importantly, a CF-TENG-based weaved fabric presents high electrical performance to meet requirements as an energy harvester. These CF-TENGs provide a significant insight to facilitate the development of fiber-based triboelectric applications.