Facile fabrication of PBS/CNTs nanocomposite foam for electromagnetic interference shielding

In order to reduce the pollutants of environment and electromagnetic waves, environment friendly polymer foams with outstanding electromagnetic interference shielding are imminently required. In this paper, a kind of electromagnetic shielding, biodegradable nanocomposite foam was fabricated by blending PBS with carbon nanotubes (CNTs) followed by foaming with supercritical CO2. The crystallization temperature and melting temperature of PBS/CNTs nanocomposites with 4 wt % of CNTs increased remarkably by 6 °C and 3.1 °C compared with that of pure PBS and a double crystal melting peak of various PBS samples appeared in DSC curves. Clearly, an increase of approximately 3 orders of magnitude was improved for storage modulus and near 9 orders of magnitude was enhanced for electrical properties with CNTs content from 0 to 4 wt %. Furthermore, CNTs endowed PBS nanocomposite foam with adjustable electromagnetic interference (EMI) shielding property, giving a specific EMI shielding effectiveness of 28.5 dB cm3/g. This study provided a promising methodology for preparing biodegradable, lightweight PBS/CNTs foam with outstanding electromagnetic shielding properties.

Tailored viscoelasticity of a polymer cellular structure through nanoscale entanglement of carbon nanotubes

A three-dimensional carbon nanotube (CNT) cellular structure presents a unique revelation of microstructure dependent mechanical and viscoelastic properties. Tailored CNT-CNT entanglement demonstrated a direct impact on both the strength and viscosity of the structure. Unlike traditional foams, an increase in the CNT-CNT entanglement progressively increases both the strength and the viscosity. The study reveals that an effective load is directly transferred within the structure through the short-range entanglements (nodes) resulting in an enhanced mechanical strength, whereas the long-range entanglements (bundles) regulate the energy absorption capacity. A three-dimensional structure of entangled CNT-CNT shows ∼15 and ∼26 times enhancement in the storage and loss moduli, respectively. The higher peak stress and energy loss are increased by ∼9.2 fold and ∼8.8 fold, respectively, compared to those of the cellular structures without entanglement. The study also revealed that the viscoelastic properties i.e. the Young's modulus, stress relaxation, strain rate sensitivity and fatigue properties can be modulated by tailoring the CNT-CNT entanglements within the cellular structure. A qualitative analysis is performed using finite element simulation to show the impact of CNT-CNT entanglements on the viscoelastic properties. The finding paves a way for designing a new class of meta-cellular materials which are viscous yet strong for shock absorbing or mechanical damping applications.

Highly Deformable Porous Electromagnetic Wave Absorber Based on Ethylene-Propylene-Diene Monomer/Multiwall Carbon Nanotube Nanocomposites

The need for electromagnetic interference (EMI) shields has risen over the years as the result of our digitally and highly connected lifestyle. This work reports on the development of one such shield based on vulcanized rubber foams. Nanocomposites of ethylene–propylene–diene monomer (EPDM) rubber and multiwall carbon nanotubes (MWCNTs) were prepared via hot compression molding using a chemical blowing agent as foaming agent. MWCNTs accelerated the cure and led to high shear-thinning behavior, indicative of the formation of a 3D interconnected physical network. Foamed nanocomposites exhibited lower electrical percolation threshold than their solid counterparts. Above percolation, foamed nanocomposites displayed EMI absorption values of 28–45 dB in the frequency range of the X-band. The total EMI shielding efficiency of the foams was insignificantly affected by repeated bending with high recovery behavior. Our results highlight the potential of cross-linked EPDM/MWCNT foams as a lightweight EM wave absorber with high flexibility and deformability.

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

Carbon nanotube/high density polyethylene (CNT/HDPE) foam composites with high electrical conductivity and electromagnetic interference (EMI) shielding performance were developed by means of compression molding plus salt-leaching. The uniform porous structure and interconnected CNT networks throughout the cell backbones endowed the as-prepared foam composites with a significantly lower electrical percolation threshold (0.22 vol%) than that of the solid composites (0.84 vol%). Owing to the multiple reflections and scattering between the cell–matrix interfaces, the foam composites presented a superior specific EMI shielding effectiveness (EMI SE) of 104.3 dB cm³ g⁻¹, 2.2 times higher than that of their solid counterpart. Besides this, the pore sizes of the CNT/HDPE foam composites could be easily tuned by controlling the particle size of the porogen. Also, the electrical conductivity and specific EMI SE increased with an increase in the cell diameter, which was attributed to the formation of a more perfect conductive network in the cell backbones. Our approach provides a novel idea for fabricating new lightweight EMI shielding materials, especially for aircraft and spacecraft applications.

Carbon nanotube/high density polyethylene foam composites with superior specific electromagnetic interference shielding effectiveness values of 104.3 dB cm³ g⁻¹ were developed via a compression molding plus salt-leaching method.

Ultralightweight silver nanowires hybrid polyimide composite foams for high-performance electromagnetic interference shielding

Ultralightweight silver nanowires (AgNWs) hybrid polyimide (PI) composite foams with microcellular structure and low density of 0.014-0.022 g/cm(3) have been fabricated by a facile and effective one-pot liquid foaming process. The tension flow generated during the cell growth induced the uniform dispersion of AgNWs throughout the cell walls. The interconnected AgNWs network in the cell walls combined with the large 3D AgNWs network caused by 3D structure of foams provided fast electron transport channels inside foams. The electromagnetic interference (EMI) shielding effectiveness (SE) of these foams increased with increasing AgNWs loading as well as the nanowire aspect ratio due to the increasing connections of the conduction AgNWs network. Appropriate surface treatment like etching or spraying facilitated the construction of the seamlessly interconnected 2D AgNWs network on the surface, which could effectively reflect electromagnetic waves. Maximum specific EMI SE of values of 1210 dB·g(-1)·cm(3) at 200 MHz, 957 dB·g(-1)·cm(3) at 600 MHz, and 772 dB·g(-1)·cm(3) at 800-1500 MHz were achieved in sprayed composite foams containing <0.044 vol % AgNWs loading, which far surpasses the best values of other composite materials. The reflections of interconnected AgNWs networks on the surface and inside foams combined with the multiple reflections at interfaces contributed to the shielding effect.

A comparative study of structure and electromagnetic interference shielding performance for silver nanostructure hybrid polyimide foams

Comparison of structure and electromagnetic interference shielding performance for silver nanostructures hybrid polyimide foams.

Facile preparation and enhanced microwave absorption properties of core–shell composite spheres composited of Ni cores and TiO2 shells

The microwave absorption properties of the core–shell Ni@rutile TiO₂ composite are superior to those of the Ni@anatase TiO₂ composite.

Polymer nanocomposite foam filled with carbon nanomaterials as an efficient electromagnetic interference shielding material

Among different carbon nanomaterial foam-filled polymer composites, graphene-based foam gives superior specific shielding effectiveness when compared to typical metals.

Preparation of a silica nanospheres/graphene oxide hybrid and its application in phenolic foams with improved mechanical strengths, friability and flame retardancy

A silica nanospheres/graphene oxide hybrid (SGO) was synthesized, and it is found that SGO can greatly improve the mechanical strengths, thermal stability and flame retardancy of phenolic foams.

Lightweight polypropylene/stainless-steel fiber composite foams with low percolation for efficient electromagnetic interference shielding

Lightweight polypropylene/stainless-steel fiber (PP-SSF) composites with 15-35% density reduction were fabricated using foam injection molding. The electrical percolation threshold, through-plane electrical conductivity, and electromagnetic interference (EMI) shielding effectiveness (SE) of the PP-SSF composite foams were characterized and compared against the solid counterparts. With 3 wt % CO2 dissolved in PP as a temporary plasticizer and lubricant, the fiber breakage was significantly decreased during injection molding, and well-dispersed fibers with unprecedentedly large aspect ratios of over 100 were achieved. The percolation threshold was dramatically decreased from 0.85 to 0.21 vol %, accounting for 75% reduction, which is highly superior, compared to 28% reduction of the previous PP-carbon fiber composite foam.1 Unlike the case of carbon fiber,1 SSFs were much longer than the cell size, and the percolation threshold reduction of PP-SSF composite foams was thus primarily governed by the decreased fiber breakage instead of fiber orientation. The specific EMI SE was also significantly enhanced. A maximum specific EMI SE of 75 dB·g(-1)·cm(3) was achieved in PP-1.1 vol % SSF composite foams, which was much higher than that of the solid counterpart. Also, the relationships between the microstructure and properties were discussed. The mechanism of EMI shielding enhancement was also studied.