Materials with good flexibility and high conductivity that can provide electromagnetic interference (EMI) shielding with minimal thickness are highly desirable, especially if they can be easily processed into films. Two-dimensional metal carbides and nitrides, known as MXenes, combine metallic conductivity and hydrophilic surfaces. Here, we demonstrate the potential of several MXenes and their polymer composites for EMI shielding. A 45-micrometer-thick Ti3C2Tx film exhibited EMI shielding effectiveness of 92 decibels (>50 decibels for a 2.5-micrometer film), which is the highest among synthetic materials of comparable thickness produced to date. This performance originates from the excellent electrical conductivity of Ti3C2Tx films (4600 Siemens per centimeter) and multiple internal reflections from Ti3C2Tx flakes in free-standing films. The mechanical flexibility and easy coating capability offered by MXenes and their composites enable them to shield surfaces of any shape while providing high EMI shielding efficiency.

Electromagnetic interference shielding with 2D transition metal carbides (MXenes)

Thermal stability and flame retardancy of polyurethanes

A review on the mechanical and electrical properties of graphite and modified graphite reinforced polymer composites

With the growing popularity of electrical communication equipment, high-performance electromagnetic interference (EMI) shielding materials are widely used to deal with radiation pollution. However, the large thickness and poor mechanical properties of many EMI shielding materials usually limit their applications. In this study, ultrathin and highly flexible Ti3C2Tx (d-Ti3C2Tx, MXene)/cellulose nanofiber (CNF) composite paper with a nacre-like lamellar structure is fabricated via a vacuum-filtration-induced self-assembly process. By the interaction between one-dimensional (1D) CNFs and two-dimensional (2D) d-Ti3C2Tx MXene, the binary strengthening and toughening of the nacre-like d-Ti3C2Tx/CNF composite paper has been successfully achieved, leading to high tensile strength (up to 135.4 MPa) and fracture strain (up to 16.7%), as well as excellent folding endurance (up to 14 260 times). Moreover, the d-Ti3C2Tx/CNF composite paper exhibits high electrical conductivity (up to 739.4 S m–1) and excellent specifi...

Binary Strengthening and Toughening of MXene/Cellulose Nanofiber Composite Paper with Nacre-Inspired Structure and Superior Electromagnetic Interference Shielding Properties

Electromagnetic energy radiation is becoming a "health-killer" of living bodies, especially around industrial transformer substation and electricity pylon. Harvesting, converting, and storing waste energy for recycling are considered the ideal ways to control electromagnetic radiation. However, heat-generation and temperature-rising with performance degradation remain big problems. Herein, graphene-silica xerogel is dissected hierarchically from functions to "genes," thermally driven relaxation and charge transport, experimentally and theoretically, demonstrating a competitive synergy on energy conversion. A generic approach of "material genes sequencing" is proposed, tactfully transforming the negative effects of heat energy to superiority for switching self-powered and self-circulated electromagnetic devices, beneficial for waste energy harvesting, conversion, and storage. Graphene networks with "well-sequencing genes" (w = Pc /Pp > 0.2) can serve as nanogenerators, thermally promoting electromagnetic wave absorption by 250%, with broadened bandwidth covering the whole investigated frequency. This finding of nonionic energy conversion opens up an unexpected horizon for converting, storing, and reusing waste electromagnetic energy, providing the most promising way for governing electromagnetic pollution with self-powered and self-circulated electromagnetic devices.

Thermally Driven Transport and Relaxation Switching Self-Powered Electromagnetic Energy Conversion.

A high-performance electromagnetic interference shielding composite based on reduced graphene oxide (rGO) and polystyrene (PS) is realized via high-pressure solid-phase compression molding. Superior shielding effectiveness of 45.1 dB, the highest value among rGO based polymer composite, is achieved with only 3.47 vol% rGO loading owning to multi-facet segregated architecture with rGO selectively located on the boundaries among PS multi-facets. This special architecture not only provides many interfaces to absorb the electromagnetic waves, but also dramatically reduces the loading of rGO by confining the rGO at the interfaces. Moreover, the mechanical strength of the segregated composite is dramatically enhanced using high pressure at 350 MPa, overcoming the major disadvantage of the composite made by conventional-pressure (5 MPa). The composite prepared by the higher pressure shows 94% and 40% increment in compressive strength and compressive modulus, respectively. These results demonstrate a promising method to fabricate an economical, robust, and highly efficient EMI shielding material.

Structured Reduced Graphene Oxide/Polymer Composites for Ultra-Efficient Electromagnetic Interference Shielding

The effects of expandable graphite (EG) of different particle sizes, on the fire-retardant properties of high-density rigid polyurethane foam (RPUF) (0.45 g cm−3) were studied. Samples of EG with different particle sizes were obtained by pulverization in an ultra-high-speed mixer for 4 and 13 min, respectively. It was shown that as received (EG0) and 4 min pulverized EG (EG4) efficiently improved the fire-retardant properties of RPUF composites, while 13 min pulverized EG (EG13) did not. The char of the burned composites filled with EG0 and EG4 covered the whole surface of the samples and formed a complete physical barrier. This barrier material prevented combustible gases from feeding the flame and also isolated oxygen efficiently from the burning material. EG13 did not produce enough char to cover the whole surface of the burning sample, resulting in poor fire-retardant property of the RPUF composites. Thermal degradation tests of the foams by thermogravimetric analysis indicated that EG showed negligible effects on the thermal stability of the RPUFs. Copyright © 2006 Society of Chemical Industry

Flame retardancy of different-sized expandable graphite particles for high-density rigid polyurethane foams

We obtained the high-density rigid polyurethane foam (RPUF) filled with expandable graphite (EG) by airtight cast molding, and its fire performance was evaluated. The results show that the LOI values increase linearly with EG content, especially the LOI value of the 20 wt% EG-filled RPUF composites increases rapidly to 39.5% from 22.5% of pure RPUF. When the pure RPUF was burned, no clear transition process between burning spots and virgin material is observed. But when the EG/RPUF composite was burned, EG produced high-volume expanded graphite and covered the surfaces of the materials, which can prevent combustible gases from feeding the flame, and it also separates oxygen from the burning material efficiently. The thermal degradation of foam was investigated using thermogravimetric analysis (TGA). The result shows that the thermo-oxidative degradation of pure RPUF takes place in the range of 220–350°C and 450–650°C, respectively. The thermal stability of RPUF composites increased slightly when ...

Expandable graphite for halogen-free flame-retardant of high-density rigid polyurethane foams

Double-segregated conductive polymer composites were fabricated as candidates for liquid sensing materials; these composites exhibited ultralow percolation (∼0.09 vol%), good reproducibility, and a large liquid sensing capacity (∼8 × 104%) with a balanced electrical conductivity (∼1 S m−1).

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Jian-Hua Wang

Papers

Structured Reduced Graphene Oxide/Polymer Composites for Ultra-Efficient Electromagnetic Interference Shielding

Flame retardancy of different-sized expandable graphite particles for high-density rigid polyurethane foams

Expandable graphite for halogen-free flame-retardant of high-density rigid polyurethane foams

Double-segregated carbon nanotube–polymer conductive composites as candidates for liquid sensing materials

Thermoelectric behaviour of segregated conductive polymer composites with hybrid fillers of carbon nanotube and bismuth telluride