Copyright © 2022 Foshan MBRT Nanofiberlabs Technology Co., Ltd All rights reserved.Site Map
Northeast Forestry University Professors Liu Zhenbo and Gan Wentao: Ti3C2Tx/Cellulose Nanofiber Composite Paper—Highly Efficient Integration of High Electrical Conductivity, Efficient Electromagnetic Shielding, and Strong Mechanical Properties
With the rapid development of 5G networks, the problem of electromagnetic pollution has become increasingly prominent. Ti3C2Tx’s excellent electrical conductivity gives it great potential in electromagnetic interference (EMI) shielding. However, its poor mechanical properties limit its further application. Currently, the main method to improve the mechanical properties of Ti3C2Tx is to introduce large amounts of flexible polymers, which causes a sharp decline in electrical conductivity and thus affects EMI shielding performance. For polymer-based EMI shielding materials, how to balance the excellent electrical conductivity, efficient EMI shielding performance, and good mechanical properties of Ti3C2Tx-based composites is a major challenge in current research, which greatly limits the application of Ti3C2Tx-based composites in practical scenarios.
Recently, the team of Professors Liu Zhenbo and Gan Wentao from Northeast Forestry University published a new research achievement “Highly electroconductive and mechanically strong Ti3C2Tx/cellulose nanofiber composite paper with gradient structure for efficient electromagnetic interference shielding” in the journal Journal of Colloid And Interface Science. The researchers used the characteristic that the total resistance in a parallel circuit is lower than the branch resistance to parallel a high electrical conductivity thin layer with a high-strength thick layer, preparing flexible Ti3C2Tx/cellulose nanofiber composite paper with a gradient structure (GS-TCCP). This design not only fully maintains the efficient conductive advantages of the high electrical conductivity layer, enabling it to continuously exhibit excellent conductive performance, but also effectively preserves the strong and tough characteristics of the high-strength layer. In addition, the unique interlayer reflection and intralayer absorption mechanisms of the gradient structure further improve the EMI shielding effectiveness (SE).GS-TCCP (Ti3C2Tx content 38.33 wt%, thickness 75 μm) not only has a high electrical conductivity of 13110 S/m and strong mechanical properties (tensile strength 78.2 MPa, toughness 4.019 MJ/m³), but also achieves an EMI SE of 46.8 dB in the X-band (8.2—12.4 GHz), with an electromagnetic interference shielding efficiency as high as 99.998%. This is comparable to homogeneous Ti3C2Tx/CNF composite paper with a Ti3C2Tx content of 50 wt% and superior to most reported Ti3C2Tx-based film composites. The balance among electrical conductivity, EMI shielding performance, and mechanical properties gives it broad application prospects in fields such as electromagnetic interference shielding, flexible sensing, and flexible electronic components.
(1) The Ti3AlC2 MAX phase was etched with a mixed acid of HF and HCl to obtain multi-layered Ti3C2Tx with an accordion-like morphology (Figure 1b). Li⁺ in LiCl solution was used for intercalation to expand the interlayer spacing. Monolayer Ti3C2Tx nanosheets were exfoliated by repeated “hand-shaking oscillation + centrifugation”. Finally, large-diameter Ti3C2Tx nanosheets were obtained by differential centrifugation. Statistical analysis of the lateral dimensions of 330 Ti3C2Tx nanosheets randomly photographed by SEM showed an average lateral dimension of 6.16 μm.
Figure 1. Preparation and characterization of large-diameter Ti3C2Tx nanosheets.
(2) A series of homogeneous Ti3C2Tx/CNF composite papers (H-TCCP) and gradient-structured Ti3C2Tx/CNF composite papers (GS-TCCP) were prepared by vacuum-assisted filtration self-assembly and alternating vacuum-assisted filtration self-assembly processes, respectively.
Figure 2. Preparation of H-TCCPs and GS-TCCPs.
(3) Due to the unique size advantage of large-diameter Ti3C2Tx nanosheets, effective contact is more easily achieved in CNFs, helping to weaken the negative impact of the electrical insulation properties of CNFs. Compared with other Ti3C2Tx-based composite films, it exhibits higher electrical conductivity. Among the four GS-TCCPs, the highest electrical conductivity was 321.0 S/cm, and the lowest was 131.1 S/cm, with little difference. The researchers constructed a corresponding mathematical model (Figure 3g) for full explanation: the function curve shows that as the resistance of the high-strength layer increases, the overall electrical conductivity of the composite paper infinitely approaches a specific value, which is consistent with the measured results.
Figure 3. Electrical conductivity of H-TCCPs and GS-TCCPs.
(4) For H-TCCPs, EMI SE gradually decreased with increasing CNF content, ranging from a maximum of 83.9 dB to a minimum of 26.8 dB; for GS-TCCPs, the maximum EMI SE was 55.5 dB, and the minimum was 42.9 dB, with total shielding efficiency exceeding 99.99%. This is mainly attributed to the electromagnetic wave loss mechanisms of interlayer reflection and intralayer absorption in the gradient structure. The EMI SE of the prepared Ti3C2Tx/CNF composite paper exceeds that of most Ti3C2Tx-based film composites.
Figure 4. EMI shielding performance of H-TCCPs and GS-TCCPs.
(5) The mechanical properties of H-TCCPs increased with increasing CNF content, with a maximum tensile strength of 130.6 MPa and a maximum toughness of 9.998 MJ/m³, far higher than pure Ti3C2Tx paper. This is attributed to the hydrogen bond interactions between CNFs and Ti3C2Tx nanosheets and the stress dispersion of high aspect ratio CNFs on Ti3C2Tx. The GS-TCCPs had a maximum tensile strength of 78.2 MPa and a minimum of 47.9 MPa, with a maximum toughness of 4.019 MJ/m³ and a minimum of 1.207 MJ/m³, all meeting the requirements for most applications. The good mechanical properties of GS-TCCPs are due to both the excellent mechanical properties of the high-strength layer itself and the energy dissipation mechanism based on interlayer friction, which dissipates external forces.
Figure 5. Mechanical properties of H-TCCPs and GS-TCCPs.
Overall, compared with H-TCCPs, GS-TCCPs exhibit more superior comprehensive performance, integrating high electrical conductivity, high electromagnetic shielding performance, and high mechanical properties, with broad application prospects in flexible electrodes, flexible sensing, electromagnetic shielding, and even extreme environments including space exploration.
