Injection Molded Segregated Carbon Nanotube/Polypropylene Composite for Efficient Electromagnetic Interference Shielding

Structural Design for EMI Shielding: From Underlying Mechanisms to Common Pitfalls

Modern human civilization deeply relies on the rapid advancement of cutting-edge electronic systems that have revolutionized communication, education, aviation, and entertainment. However, the electromagnetic interference (EMI) generated by digital systems poses a significant threat to the society, potentially leading to a future crisis. While numerous efforts are made to develop nanotechnological shielding systems to mitigate the detrimental effects of EMI, there is limited focus on creating absorption-dominant shielding solutions. Achieving absorption-dominant EMI shields requires careful structural design engineering, starting from the smallest components and considering the most effective electromagnetic wave attenuating factors. This review offers a comprehensive overview of shielding structures, emphasizing the critical elements of absorption-dominant shielding design, shielding mechanisms, limitations of both traditional and nanotechnological EMI shields, and common misconceptions about the foundational principles of EMI shielding science. This systematic review serves as a scientific guide for designing shielding structures that prioritize absorption, highlighting an often-overlooked aspect of shielding science.

Transformation from Electromagnetic Inflection to Absorption of Silicone Rubber and Accordion-Shaped Ti3C2MXene Composites by Highly Electric Conductive Multi-Walled Carbon Nanotubes

Electromagnetic (EM) pollution becomes more penetrating in daily life and work due to more convenience provided by multi-electrical devices, as does secondary pollution caused by electromagnetic reflection. EM wave absorption material with less reflection is a good solution to absorb unavoidable EM radiation or reduce it from the source. Filled with two-dimensional Ti₃SiC₂MXenes, silicone rubber (SR)composite demonstrated a good electromagnetic shielding effectiveness of 20 dB in the X band by melt-mixing processes for good conductivity of more than 10^-3 S/cm and displayed dielectric properties and a low magnetic permeability; however, the reflection loss was only -4 dB. By the combination of one-dimensional highly electric conductive multi-walled carbon nanotubes (HEMWCNTs) and MXenes, the composites achieved the transformation from electromagnetic inflection to an excellent absorbing performance to reach a minimum reflection loss of -30.19 dB due to electric conductivity of above 10^-4 S/cm, a higher dielectric constant, and more loss in both dielectric and magnetic properties. Ni-added multi-walled carbon nanotubes were not able to achieve the transformation. The as-prepared SR/HEMWCNT/MXene composites have potential application prospects in protective layers, which can be used for electromagnetic wave absorption, electromagnetic interference suppression of devices, and stealth of the equipment.

Electromagnetic Shielding Enhancement of Butyl Rubber/Single-Walled Carbon Nanotube Composites via Water-Induced Modification

Electromagnetic properties of polymer composites strongly depend on the loading amount and the completeness of the filler's dispersive structure. Improving the compatibility of single-walled carbon nanotubes (SWCNTs) with isobutylene butyl rubber (IIR) is a good solution to mitigate aggregation. The change in configuration of poly-oxyethylene octyl phenol ether (OP-10) was induced using water as the exposed hydrophilic groups linking with water molecules. The SWCNT and IIR/SWCNT composites were then prepared via wetly-melt mixing at a relatively high temperature to remove water, and they were then mixed with other agents after vacuum drying and cured. The SWCNTs were dispersed uniformly to form a good network for a lower percolation threshold of the wave-absorbing property to 2 phr from 8 phr. With 8 phr SWCNTs, the tensile strength of the material improved significantly from 7.1 MPa to 15.1 MPa, and the total electromagnetic shielding effectiveness of the material was enhanced to 23.8 dB, a 3-fold increase compared to the melt-mixed material. It was demonstrated that water-induced modification achieved good dispersion of SWCNTs for electromagnetic shielding enhancement while maintaining a wide damping temperature range from -55 °C to 40 °C with a damping factor over 0.2.

Bio-Based Eucommia ulmoides Gum Composites with High Electromagnetic Interference Shielding Performance

Herein, high-performance electromagnetic interference (EMI) shielding bio-based composites were prepared by using EUG (Eucommia ulmoides gum) with a crystalline structure as the matrix and carbon nanotube (CNT)/graphene nanoplatelet (GNP) hybrids as the conductive fillers. The morphology of the CNT/GNP hybrids in the CNT/GNP/EUG composites showed the uniform distribution of CNTs and GNPs in EUG, forming a denser filler network, which afforded improved conductivity and EMI shielding effect compared with pure EUG. Accordingly, EMI shielding effectiveness values of the CNT/GNP/EUG composites reached 42 dB in the X-band frequency range, meeting the EMI shielding requirements for commercial products. Electromagnetic waves were mainly absorbed via conduction losses, multiple reflections from interfaces and interfacial dipole relaxation losses. Moreover, the CNT/GNP/EUG composites exhibited attractive mechanical properties and high thermal stability. The combination of excellent EMI shielding performance and attractive mechanical properties render the as-prepared CNT/GNP/EUG composites attractive candidates for various applications.

A Healable and Mechanically Enhanced Composite with Segregated Conductive Network Structure for High-Efficient Electromagnetic Interference Shielding

The cationic waterborne polyurethanes microspheres with Diels-Alder bonds were synthesized for the first time. The electrostatic attraction not only endows the composite with segregated structure to gain high electromagnetic-interference shielding effectiveness, but also greatly enhances mechanical properties. Efficient healing property was realized under heating environment. It is still challenging for conductive polymer composite-based electromagnetic interference (EMI) shielding materials to achieve long-term stability while maintaining high EMI shielding effectiveness (EMI SE), especially undergoing external mechanical stimuli, such as scratches or large deformations. Herein, an electrostatic assembly strategy is adopted to design a healable and segregated carbon nanotube (CNT)/graphene oxide (GO)/polyurethane (PU) composite with excellent and reliable EMI SE, even bearing complex mechanical condition. The negatively charged CNT/GO hybrid is facilely adsorbed on the surface of positively charged PU microsphere to motivate formation of segregated conductive networks in CNT/GO/PU composite, establishing a high EMI SE of 52.7 dB at only 10 wt% CNT/GO loading. The Diels-Alder bonds in PU microsphere endow the CNT/GO/PU composite suffering three cutting/healing cycles with EMI SE retention up to 90%. Additionally, the electrostatic attraction between CNT/GO hybrid and PU microsphere helps to strong interfacial bonding in the composite, resulting in high tensile strength of 43.1 MPa and elongation at break of 626%. The healing efficiency of elongation at break achieves 95% when the composite endured three cutting/healing cycles. This work demonstrates a novel strategy for developing segregated EMI shielding composite with healable features and excellent mechanical performance and shows great potential in the durable and high precision electrical instruments.

Microwave-Assisted Sintering to Rapidly Construct a Segregated Structure in Low-Melt-Viscosity Poly(Lactic Acid) for Electromagnetic Interference Shielding

Formation of a segregated structure in conductive polymer composites is one of the most effective strategies for achieving good electrical conductivity and electromagnetic interference (EMI) shielding performance. Nevertheless, for low-melt-viscosity poly(lactic acid) (PLA), intense molecular motion occurs at the molding temperature, which is detrimental to the fixation of the conductive networks. In this study, a novel molding technique assisted by microwave heating was proposed to construct a segregated structure in a PLA/carbon nanotube (CNT) composite. The coating layer of CNTs acted as the microwave absorber and caused intense localized heating of PLA surfaces upon microwave irradiation. The surface temperature of the PLA granule was precisely regulated by adjusting the coated CNT content, microwave power, and irradiation time. Thus, the coated granules were softened and fused at an optimal sintering zone, which effectively hindered the excessive migration of CNT strips into the interior of PLA phases, and a majority retained the original CNT network in the molded composite. Meanwhile, benefiting from microwave sintering, sufficient chain diffusion and entanglement occurred in the interfacial regions, enhancing the adhesion strength among the neighboring PLA phases. The prepared PLA/CNT composite with only 5.0 wt % CNTs exhibited a high electrical conductivity of 16.3 S/m and an excellent EMI shielding effectiveness (EMI SE) of 36.7 dB at a frequency of 10.0 GHz. The results indicate that microwave-assisted sintering might be a promising alternative for constructing a segregated structure in low-melt-viscosity polymers.

Facile Fabrication of Nickel Aluminum Layered Double Hydroxide/Carbon Nanotube Electrodes Toward High-Performance Supercapacitors

The electrode, as one of the key components in supercapacitors, has a pivotal effect on the overall performances. In this work, a series of composite electrode materials are proposed via the combination of nickel aluminum layered double hydroxides (NiAl-LDHs) and carbon nanotubes (CNTs). To begin with, materials with different ratios of the two compositions are fabricated with a coprecipitation method. After that, various characterization methods indicate that the NiAl-LDH/CNT composites exhibit an irregular thin platelet structure with a well-constructed conductive network inside. Furthermore, the effect of the CNT ratio on the electrochemical property is subsequently investigated, which proves that the conductive network of CNTs is beneficial for the transport of the electrons and strengthens the platelet structure. The results show that when the amount of CNTs reaches 1.5 wt %, it can yield a high specific capacitance of 2447 F g^-1 at 2 A g^-1, with a good cycling stability of 90.1% after 2500 cycles, indicating high application potential in positive electrodes of pseudocapacitors. The synergistic effects of NiAl-LDHs and CNTs are thought to be the main reasons for the good properties of NiAl-LDHs/CNTs composites.

Segregated poly(arylene sulfide sulfone)/graphene nanoplatelet composites for electromagnetic interference shielding prepared by the partial dissolution method

Segregated conductive polymer composites have been proved to be outstanding electromagnetic interference shielding (EMI) materials at low filler loadings. However, due to the poor interfacial adhesion between the pure conductive filler layers and segregated polymer granules, the mechanical properties of the segregated composites are usually poor, which limit their application. Herein, a simple and effective approach, the partial dissolution method, has been proposed to fabricate segregated poly(arylene sulfide sulfone) (PASS)/graphene nanoplatelet (GNP) composites with superior EMI shielding effectiveness (SE) and high tensile strength. Morphology examinations revealed that the GNPs were restricted in the dissolved outer layer by the undissolved cores, and there was a strong interaction between the PASS/GNP layer and the pure PASS core. The resultant PASS/GNP composites showed excellent electrical conductivity (60.3 S m-1) and high EMI SE (41 dB) with only 5 wt% GNPs. More notably, the tensile strength of the PASS/GNPs prepared by partial dissolution reached 36.4 MPa, presenting 136% improvement compared to that of the conventional segregated composites prepared by mechanical mixing. The composites also exhibited high resistance to elevated temperatures and chemicals owing to the use of the special engineering polymer PASS as a matrix.