Efficient electromagnetic interference shielding of lightweight carbon nanotube/polyethylene compositesviacompression molding plus salt-leaching

Enhanced Electromagnetic Interference Shielding Properties of CNT/Carbon Composites by Designing a Hierarchical Porous Structure

With the widespread use of electronic devices, electromagnetic interference (EMI) has become an increasingly severe issue, adversely affecting device performance and human health. Carbon nanotubes (CNTs) are recognized for their electrical conductivity, flexibility, and stability, making them promising candidates for EMI shielding applications. This research developed hierarchical porous-structured CNT/carbon composites for enhancing electromagnetic interference (EMI) shielding properties. Featuring a CNT film with nano-scale pores and an amorphous carbon layer with micro-scale pores, the CNT/carbon composites are strategically arranged to promote the penetration of EM waves into the composite's interior and facilitate multiple reflections, thereby improving the EMI shielding performance. An impressive EMI shielding effectiveness of 61.4 dB was achieved by the CNT/carbon composites, marking a significant improvement over the 36.5 dB measured for the pristine CNT film. Owing to the micro pores in the amorphous carbon layer, a notable reduction in the reflection shielding efficiency (SER) but, concurrently, a substantial increase in the absorption shielding efficiency (SEA) compared with the pristine CNT film was realized in the composites. This study successfully validated the effectiveness of the hierarchical porous structure in enhancing the EMI shielding performance, providing a promising new strategy for the development of lightweight, flexible, and efficient EMI shielding materials.

Development of biochar/HDPE composites and characterization of the effects of carbon loadings on the electromagnetic shielding properties

The aim of this research is to develop high carbon-yielding biochar from pinewood, coffee husk, sugarcane bagasse, and maize cob and to characterize the biochar/HDPE composites for electromagnetic (EM) shielding application. During the biochar/HDPE composites fabrication, slow pyrolysis and compression molding manufacturing were used. The enhanced properties characterizations were conducted by using thermogravimetric analysis (TGA), scanning electron microscopy (SEM), differential thermal analysis (DTA), Fourier transform spectrometry (FTIR), Brunauer-Emmet-Teller (BET) analysis, digital multi-meter, and proximity analysis. The results of biochar pyrolysis showed the maximum carbon yield of 74.6 %, 68.9 %, 68.4 %, and 40 % for pine wood, maize cob, sugarcane bagasse, and coffee husk respectively. The BET analysis showed the maximum specific surface area (734.5 m2/g), pore volume (0.2364 cm3/g), and pore radius (9.897 Å) from the pine wood biochar. The biochar loading analysis results showed that the 30 % and 40 % pine wood biochar significantly enhanced the electrical conductivity, thermal conductivity, thermal stability, crystallinity, and EM shielding effectiveness (SE) of the biochar/HDPE composites. In particular, the biochar/HDPE composite with 30 wt% pine wood biochar showed the highest thermal conductivity of 2.219 W/mK, and the 40 wt% pine wood biochar/HDPE composite achieved the highest electrical conductivity of 4.67 × 10-7 S/cm and EM SE of 44.03 dB at 2.1 GHz.

Visualization of Deep Convolutional Neural Networks to Investigate Porous Nanocomposites for Electromagnetic Interference Shielding

Constructing porous structures in electromagnetic interference (EMI) shielding materials is a common strategy to decrease the secondary pollution caused by the reflection of electromagnetic waves (EMWs). However, the lack of direct analysis methods makes it difficult to fully understand the effect of porous structures on EMI, hindering EMI composites' development. Furthermore, while deep learning techniques, such as deep convolutional neural networks (DCNNs), have significantly impacted material science, their lack of interpretability limits their applications to property predictions and defect detection tasks. Until recently, advanced visualization techniques provided an approach to reveal the relevant information behind DCNNs' decisions. Inspired by it, a visual approach for porous EMI nanocomposite mechanism studies is proposed. This work combines DCNN visualization with experiments to investigate EMI porous nanocomposites. First, a rapid and straightforward salt-leaked cold-pressing powder sintering method is employed to prepare high-EMI CNTs/PVDF composites with various porosities and filler loadings. Notably, the solid sample with 30 wt % loading maintains an ultrahigh shielding effectiveness of 105 dB. The influence of porosity on the shielding mechanism is discussed macroscopically based on the prepared samples. To determine the shielding mechanism, a modified deep residual network (ResNet) is trained on a dataset of scanning electron microscopy (SEM) images of the samples. The Eigen-CAM visualization of the modified ResNet intuitively shows that the amount and depth of the pores impact the shielding mechanisms and that shallow pore structures contribute less to EMW absorption. This work is instructive for material mechanism studies. Besides, the visualization has the potential as a porous-like structure marking tool.

Injection-molded lightweight and high electrical conductivity composites with microcellular structure and hybrid fillers

Polypropylene/carbon black (PP/CB) and PP/CB/multiwalled carbon nanotube (PP/CB/MWCNT) composites were fabricated by solid and foam injection molding, with the goal of enhancing the electrical conductivity of the composites while decreasing the cost of the final product. The foaming behavior and through-plane (T-P) electrical conductivity of the composites were characterized and analyzed. Cell growth increased the interconnection of the conductive fillers, changed the filler orientation, and enhanced the T-P electrical conductivity of the composites. Under appropriate processing conditions (200°C melt temperature, 70 cm3/s injection flow rate, and 5% void fraction), the T-P electrical conductivity of the foam PP/CB composites was 5 orders of magnitude higher than that of the solid composites (from 5.877 × 10−12 S/m to 1.010 × 10−7 S/m). Moreover, the T-P electrical conductivity values of the PP/CB and PP/CB/MWCNT were compared at the same conductive fillers content (15 wt%). The results showed that the T-P electrical conductivity of the PP/CB/MWCNT composites was far higher than that of the PP/CB composites by almost five orders of magnitude because the MWCNT acted as a bridge between CB particles, and a unique geometric shape was formed in the system. The T-P electrical conductivity of the foam PP/CB/MWCNT composites with 15 wt% carbon fillers was higher than that of the solid PP/CB composites with 20 wt% carbon fillers. This study reveals that the effect of foaming and the addition of hybrid fillers can improve the T-P electrical conductivity of plastic products, which is very important for the development of lightweight conductive plastics.

High absorption shielding material of poly(phthalazinone etherketone)/multiwall carbon nanotube composite films with sandwich configurations

Sandwich structure can be induced to achieve excellent electromagnetic interference shielding effectiveness (EMI SE) as is well known. However, how to optimize the structure to achieve performance optimization is still a problem. Herein, a poly(phthalazinone etherketone)/multiwall carbon nanotube (PPEK/MWCNT) composite with homodisperse and high content (15 wt%) of MWCNT was prepared by a water induced phase separation process. A sandwich structure was designed by introducing a wave-transmitting layer between the PPEK/MWCNT composite films. The MWCNT loading of the shielding layer and the wave-transmitting layer thickness (d) were varied to systematically investigate their influence on shielding performance in the X-band (8.2–12.4 GHz). EMI SE shows strong d value dependence. When the shielding layer was fixed, EMI SE showed a trend of decreasing, rising, leveling off and then decreasing again with d value increasing. The d value in the leveling off stage is the best value for performance optimization. The best d value decreased with increasing MWCNT content of the shielding layer. An absorption dominated SE up to 65 dB and a high increment rate of 140% of SE were achieved by optimization of the d value and shielding layer.

Sandwich structure can be induced to achieve excellent electromagnetic interference shielding effectiveness (EMI SE) as is well known.

Oxidized multiwall carbon nanotube/silicone foam composites with effective electromagnetic interference shielding and high gamma radiation stability

Oxidized multiwall carbon nanotubes (o-MWCNTs) were introduced into silicone foam to fabricate an electromagnetic interference (EMI) shielding material with high gamma radiation stability by solution casting followed by foaming and cross-linking reactions. The as-prepared o-MWCNT/silicone foam composites exhibited excellent mechanical strength and effective EMI shielding properties with superior EMI shielding effectiveness (SE) ranging from 26 to 73 dB at a 0.5-6.4 mm thickness with 30 wt% o-MWCNTs in the Ku band. Moreover, the composites have good gamma radiation stability, showing relatively stable EMI shielding properties and an improvement of hardness and pressure resistance after gamma irradiation with the absorbed dose of 500 kGy. These results indicate that the o-MWCNT/silicone foam composite is an attractive candidate for EMI shielding in some ionizing radiation environments.