Based on the current rapid development of electronic products, the development of light-weight, processable, environmentally friendly, long-life, durable, less corrosive, and tunable conductive composite materials with multiple applications may be the development direction of next-generation electronic devices. In this work, for the first time, we employed 3-Mercaptopropyltrimethoxysilane (3-MT) to modify viscose nonwovens and enhance the copper plating process. The prepared samples were characterized by Fourier transform infrared, Wide-angle X-ray diffraction (WAXD), scanning electron microscope + energy dispersive X-ray spectroscopy (SEM + EDS), thermogravimetric analysis (TGA), electrical resistivity, anti-corrosion, Joule heating, and electromagnetic interference (EMI) shielding. Results showed that 3-MT was covalently bound to the viscose surface through hydrolysis and condensation reactions and introduced SH groups. WAXD confirmed that the thiol modification did not change the internal crystal structure of viscose and copper ions. TGA and surface morphology analysis confirmed that the modified viscose promoted the deposition of metal particles in the copper plating process due to the affinity of thiol to metal so that copper particles almost completely wrapped the viscose fibers. In addition, 3MT@Cu@Viscose exhibits extremely low surface and volume resistivity (346.6 and 333.2 mΩ·m), improved corrosion resistance (corrosion rate reduced by 58% compared to the unmodified sample), fast Joule heating response (within 10 s) in low voltage (1 V) and excellent EMI shielding effectiveness (EMI SE > 50 dB). It showed great potential in future multi-functional electronic products such as electric heating sensors, smart clothing, and EMI shielding barrier.
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Introduction
With the development of society and technology, people's lives and work increasingly depend on electronic products, such as mobile phones, smart watches, health testing equipment, computers, etc. Therefore, a huge amount of electronic-waste (e-waste) is also generated. According to reports, a total of 53.6 million tons of e-waste was generated globally in 2019, of which only 17% was recycled (Shahabuddin et al. 2022). It poses a huge challenge to the environment and human health. Because some electronic products contain toxic halogen metals and plastic polymers, etc. (Ilankoon et al. 2018), at the same time, the electromagnetic radiation produced by electronic products and communication equipment may also have bad effects on the human body (Raghu et al. 2022). In this regard, the development of environmentally friendly, easily processable, multifunctional conductive composite is an ideal candidate for next-generation electronics (Zhao et al. 2021).
Viscose fiber is made of regenerated cellulose as the main raw material and is transformed into fiber by various wet spinning processes. Cellulose is recognized as an environmentally friendly material that can be extracted from plants and has a wide range of sources (Tan et al. 2022). At the same time, it also has the advantages of low cost, and easy degradation, and shows great potential in flexible high-strength polymer substrates in the future (Zhao et al. 2021). Although the cellulose-based material is so attractive, it is still an insulating material itself, and how to make it conductive is also a hot topic for many researchers.
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Many approaches have been attempted to impart conductivity to cellulose-based materials, such as surface coating, doping, interfacial assembly/encapsulation (Zhu et al. 2019; Li et al. 2020; Wang et al. 2020). Wang et al. (2020) sandwiched silver nanowires between regenerated cellulose membranes (as a flexible substrate) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) and successfully prepared flexible conductors. It has good performance as a strain sensor (Wang et al. 2020). However, as far as we know, 3,4-Ethylenedioxythiophene has acute cytotoxicity, so there are risks in its preparation and use. Han et al. (2021) developed cellulose-based Ni-decorated graphene magnetic film. However, this work needs to be carried out under high pressure for over 12 h and the process is complicated, thus limiting its development. Copper nanoparticles have garnered significant attention in recent years owing to their affordability and ease of production. Presently, various methods are available for the synthesis of copper nanoparticles, including chemical reduction (Komeily-Nia et al. 2013), vapor deposition (Eom et al. 2021), vapor evaporation (Poudel et al. 2021), and electrolysis (Nikolić et al. 2019). Among these methods, chemical reduction deposition stands out as a relatively straightforward approach. By adjusting factors such as the copper solution's concentration, pH value, and the concentration of the reducing solution, one can easily obtain the desired copper nanoparticles. In accordance with Sedighi et al. (2014) theory, as the reaction progresses, the nanoparticles infiltrate the fabric, and Cu2+ ions undergo reduction to Cu+ ions through interaction with the hydroxyl groups present in cellulose. The reducing agent has the capacity to further reduce additional copper salts, ultimately leading to the formation of zero-valent copper nanoparticles.
3-Mercaptopropyltrimethoxysilane (3-MT) has an SH group. It is often used as a metal surface rust inhibitor and activator to treat gold, silver, copper, and other metal surfaces to improve their oxidation corrosion resistance and adhesive properties to polymer materials. At present, some studies mainly focus on the surface activation of nano-metal particles, functionalization of graphene oxide materials (Chowdury et al. 2021; Zhang et al. 2021; Kumar et al. 2022). Huang et al. (2020) improved the flame retardancy of 3-MT functionalized graphene oxide paper, which has good performance in fire prevention and fire alarm. Chowdury et al. (2022) functionalized nanohybrid graphene oxide membranes with 3-MT and used them in proton exchange membranes.
However, as we know, many people utilize 3MT-modified cellulose-based materials mainly for solution adsorption and interface improvement (Rong et al. 2018; Zeng et al. 2019; Zhang et al. 2022). It has never been used to prepare conductive cellulose-based materials and their electrical applications.
In this work, the modification of viscose nonwovens using 3MT followed by electroless copper plating is proposed for the first time. The results showed that the viscose was successfully modified and greatly improved the performance of copper plating. Its surface and volume resistivity is significantly reduced, and it has an excellent performance in Joule heating, corrosion resistance, and electromagnetic interference (EMI) shielding. This method provides new ideas and references for the modification of oxygen-containing polymers and the surface plating of copper or other metals. The prepared materials have potential applications in many fields.
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Materials and tests
The substrate was a viscose nonwoven (density: 47 g/m2; thickness: 0.33 mm), which was obtained from Technical University of Liberec. Ethanol, acetone, hydrochloric acid (HCl), copper sulfate pentahydrate (CuSO4·5H2O), sodium borohydride (NaBH4), Ethylenediaminetetraacetic acid (EDTA), potassium sodium tartrate (NaKC4H4O6), NaOH and (3-Mercaptopropyl) triethoxysilane (3-MT) were supplied by Sigma Aldrich (ST. Louis, USA). All the solutions used distilled water with 18 MΩ cm electrical resistivity.
Thiol modified viscose
Firstly, 30 ml 80% ethanol solution was prepared and its pH was adjusted to 4.0 by HCl. Then, 5 wt% 3-MT solution was added into the above ethanol solution and stirred for 30 min to facilitate its full hydrolysis. Subsequently, viscose fabric was added into the above 3-MT solution for thiol modification and stirred at slow speed for 2 h at 80 °C. After the reaction, the fabric was taken out and dried in the oven at 120 °C for 10 min to promote modification. Finally, samples were washed in ethanol and acetone solutions to remove unreacted 3-MT. Herein, the modified viscose fabric was named 3MT@Viscose. The possible reaction process is shown in Fig. 1.
Fig. 1
Possible reaction mechanisms regarding thiol-modified viscose
×
Copper coating of thiol modified viscose
The 3MT@Viscose was taken into an electroless copper plating bath in 50 ml quantity. At first, according to our previous study, 14.5 g/L EDTA, 14 g/L NaKC4H4O6, and 15 g/L CuSO4·5H2O were mixed in 50 ml distilled water as a copper plating bath (pH 13). Then, 3MT@Viscose and 2 g/L NaBH4 were added into this bath. The process was carried out at room temperature under mechanical stirring until the end of the reaction (the solution became clear). The copper-plated 3MT@Viscose fabric was obtained after washing with deionized water several times and drying in the oven at 80 °C for 30 min. The copper-plated 3MT@Viscose fabric was named 3MT@Cu@Viscose. For comparison, we prepared copper-plated unmodified viscose fabric under the same conditions, and the sample was named Cu@Viscose.
FTIR and WAXD test
Fourier transform infrared spectroscopy (FTIR) analysis was performed using the Nicolet 6700 reflection ATR technique on an adapter with a diamond crystal. Before and after the action of ozone gas, the crystalline structure of samples was investigated using wide-angle X-ray diffraction by means of an X’Pert Pro System (PAN alytical, The Netherlands) with a Cu Kα (λ = 0.154 nm) source operating at 40 kV and 30 mA (Maqsood et al. 2017). The diffraction profiles were obtained in the 2θ range 10–60° with 0.02° steps. The d-spacing of the crystalline structure of the copper surface layer of samples was calculated by Bragg`s law:
where \({d}_{(200)}\) is the d-spacing in the orthogonal direction (z direction) to the substrate, \(\lambda\) is the X-ray wavelength, and \(\theta\) is the X-ray diffraction angle of the given crystal.
The thickness of the surface layer of samples was calculated in (2 0 0) direction, orthogonal direction to the substrate by Scherrer`s equation:
$$L_{200} = \frac{K\lambda }{{B\cos \theta }}$$
(2)
where K is the Scherrer constant, 0.9, \(\lambda\) is the X-ray wavelength, \(\theta\) is the X-ray diffraction angle of the investigated crystal, and B is the full width at half-maximum (FWHM).
Additionally, the supramolecular structural changes of viscose substrates was analyzed by the estimation of crystallinity. The numerical calculation was obtained by the use WAXSFIT software based on Hindeleh and Johnson’s method (Rabiej 2013):
where \({\chi }_{c}\) is crystallinity degree, AA and AC are the integral intensities of the amorphous halo and the peaks originating from the crystalline phase, respectively.
Morphology test
The surface morphology of samples was observed by Scanning electron microscope (SEM), Nova nanoSEM 230 (FEI Europe B.V., Eindhoven, The Netherlands) with energy dispersive X-ray spectroscopy (EDS) Apollo (EDAX, Mahwah, NJ, USA). The quantitative EDS analysis was carried out by the use ZAF correction procedures.
Resistivity test
The surface and volume resistance of samples was measured according to the standard EN 1149–1:2008 Protective clothing-Electrostatic properties. Sample conditioning (24 h) and measurements were performed under isothermal conditions (T = 23 °C) at a relative humidity value of 25% in a conditioning chamber. The electrical resistances of the studied samples were measured along the longitudinal direction using a ring electrode (d = 6.9 cm, D = 8.9 cm), a Keithley 610 C electrometer (Keithley Instruments Inc., Cleveland, OH, USA) and a Statron stabilized power supply of unit type 4218 (Statron AG, Mägenwil, Switzerland) (Skrzetuska et al. 2014). According to European Standards, the surface resistivity (ρs) was calculated by the equation:
$$\rho_{s} = R_{s} \cdot \frac{o}{l}$$
(4)
where \({\rho }_{s}\) is the surface resistivity (Ω); \({R}_{s}\) is surface resistance (Ω); \(o\) is the middle perimeter of electrodes (m), and \(l\) is the distance between electrodes (m).
The volume resistivity (ρs) was calculated by the equation:
$$\rho_{v} = R_{V} \cdot \frac{S}{h}$$
(5)
where \({\rho }_{v}\) is the volume resistivity (Ω·m); \({R}_{V}\) is volume resistance (Ω); \(S\) is the area of electrodes (m2) and \(h\) is the thickness of samples (m).
Thermal test
Using TGA/SDTA851 (Mettler Toledo), a 1–10 mg sample was measured from 50–600 °C at a heating rate of 10 °C /min under N2 conditions.
Joule heating test
Both sides of 3MT@Cu@Viscose and Cu@Viscose were fixed by electrode clips, and the distance between the electrodes at both ends was 3 cm. Then, DC power was connected and output different voltages (0.5 and 1 V for 3MT@Cu@Viscose, 5 and 10 V for Cu@Viscose). Applied current range from 0.5 to 1 A. Changes in temperature were monitored by the thermal camera.
Anti-corrosion properties
This test was performed in an electrochemical workstation (ZDJ-4A). Firstly, 200 ml 3 wt% NaCl solution was prepared as an electrolyte and placed in a three-necked flask. The prepared 3MT@Cu@Viscose and Cu@Viscose were used as the working electrode, the platinum electrode was used as the auxiliary electrode, and the saturated calomel electrode (SCE) was used as the reference electrode. Then, setting the initial potential to −0.2 V and the termination potential to 0.2 V (relative to the open circuit potential), the scan rate to 0.5 mV/s, the potential interval to 0.5 mV, and the sampling rate to 4 Hz.
EMI shielding test
To evaluate the effectiveness of EMI shielding, we employed the coaxial transmission line method outlined in ASTM 4935–10 (Hu et al. 2022). This standard assumes that a plane wave impacts a shielding material within the frequency range of 30 MHz–3 GHz. Our testing equipment included a coaxial specimen holder (EM-2107A), supplied by Electro-Metrics, Inc., and a vector network analyzer (ZNC3) from A Rhode & Schwarz. The analyzer is capable of generating and receiving electromagnetic signals, and we used it to calculate the SE (forward transmission coefficient S21) both with and without the shielding material. The calculation formula is given by the following equation:
where \({P}_{1}\) is the received power without the fabric present, \({P}_{2}\) is the received power with the fabric present. The ratio of the receiving reflected power (\({P}_{3}\)) and the received power without the fabric present (\({P}_{1}\)) calculates the input reflection coefficient by the following equation:
$$S11 = 10Log\frac{{P_{3} }}{{P_{1} }}$$
(7)
The measurements were performed under the following laboratory conditions: T = 23.9 °C ± 2 °C, RH = 48% ± 5%. Each sample was measured five times at different locations.
Results
Characterization of thiol modified viscose
To study the chemical interaction between viscose and 3MT after the reaction, original viscose and 3MT@Viscose were selected for comparison. Figure 2 shows the comparison of FTIR spectra of original viscose and 3MT@Viscose. Firstly, the characteristic bands appearing around 3350 cm−1 and 2920 cm−1 are attributed to the O–H stretching vibration and C–H stretching vibration of the hydrogen bonding of cellulose molecules in viscose (Ogunjobi et al. 2023). The band at 1700 cm−1 may be caused by the O–H bending vibration of water molecules (Dong et al. 2020). In addition, there are many new characteristic bands appear in the 3MT@Viscose after modification. The characteristic band observed around 1260 cm−1 is due to the vibration of CH3 of 3MT. Interestingly, after 3MT modification, the characteristic band of cellulose at 1060 cm−1, which was attributed to the C–O–C stretching vibration of the glycoside ring shifted to 1020 cm−1, confirming the existence of its Si–O–Si chain (Kim et al. 2023; Tan et al. 2023). In addition, the bands appearing around 800 cm−1 are attributed to Si–C bonds (Beaumont et al. 2018). The appearance of these bands confirms that complete hydrolysis of 3MT achieved the successful modification of 3MT@Viscose.
Fig. 2
FTIR spectra of original viscose and 3MT@Viscose
×
It can be seen from XRD in Fig. 3 that all samples have the two dominated peaks around 2θ: 20.0° and 22°, corresponding to the \((1 1 0)\) and (0 2 0) lattice planes of regenerative cellulose II structures (French 2014). The numerical deconvolution of the X-ray diffraction profiles allows to the analysis the supramolecular structure changes of cellulose II in the copper plating process (Fig. S1). The insignificant decrease of crystalline degree was observed only in the case of application 3MT, what probably slightly damaged structure of cellulose. On the other hand, the the copper plating did not result in the significant changes of the supramolecular structure of the substrates. The absence of supramolecular changes or their insignificant nature show that the chosen surface modification method is suitable for viscose substrates.
Fig. 3
XRD of original viscose, 3MT@Viscose, Cu@Viscose and 3MT@Cu@Viscose
×
After copper plating, the copper thin layer exists in the form of crystalline copper on the adhesive surface, and sharp peaks appear around 43° and 50.6°, corresponding to (1 1 1) and (2 0 0) copper lattice planes, indicating that the successful coating of copper ions without undesirable products such as oxides. Calculated by the Bragg’s equation and Scherrer formula, the sample crystal structure, lattice spacing and crystallite size suggest the insignificant influence of the thiol modification only on the obtained layer thickness (Table 1). The sample modification without 3MT allows to the creation of the copper layer thicker around 2 nm.
Table 1
Structural parameters of samples in the WAXD test
Name
Cellulose II
Coopper layer
χC (%)
d(200) (nm)
L(200) (nm)
Viscose
56.9
–
–
3MT@Viscose
53.5
–
–
Cu@Viscose
56.2
0.181
13.66
3MT@Cu@Viscose
52.5
0.179
11.34
Surface morphology and elements analysis of different samples
The morphology of viscose, 3MT@Viscose, Cu@Viscose and 3MT@Cu@Viscose is shown in Fig. 4. From Fig. 4, It can be clearly seen that there are no other particles deposited on the surface of the original viscose and 3MT@viscose. Combined with EDS (Table 2), it was found that Si and S elements were grafted onto the surface of the modified viscose and distributed uniformly, indicating the successful chemical modification of thiol. Similar elements can also be seen on 3MT@Cu@Viscose. After copper plating, the deposition of surface copper particles was clearly observed. According to the EDS results, the thiol-modified viscose has a stronger attraction to copper and adsorbs more copper particles. This may be because the 3MT molecule contains a deprotonated thiol group, which is capable of forming strong complexes with metal ions in alkaline plating baths, resulting in a high density of copper ions on the particle surface (Mondin et al. 2013).
Fig. 4
SEM and EDS of original viscose, 3MT@Viscose, Cu@Viscose and 3MT@Cu@Viscose
Table 2
EDS quantitative analysis of elements on viscose surface
Element (wt%)
Viscose
3MT@Viscose
Cu@Viscose
3MT@Cu@Viscose
C
46.51
44.39
33.74
10.33
O
53.49
43.45
21.73
6.35
Si
–
5.96
–
0.74
S
–
6.19
–
0.61
Cu
–
–
44.54
81.97
Total
100.00
100.00
100.00
100.00
×
By carefully comparing Cu@Viscose and 3MT@Cu@Viscose, we can find from Fig. 5 that the modified viscose fiber is almost completely covered by copper particles, and the accumulated copper particles are very dense, forming a large rock-like particles with a very compact structure. It may be attributed to the fact that once the thiol-coated particles have formed the initial metal nuclei, the deposition process becomes autocatalytic, as the previously plated metal acts as a catalyst for the deposition of the remaining metal ions in solution (Djokić 2002; Mondin et al. 2013). In contrast to the unmodified viscose, copper particles are less deposited on the surface of the fiber, and the accumulation forms a very loose line-like structure. In short, the viscose modified by 3MT is better for complexing with copper due to the presence of SH groups on its surface.
Fig. 5
SEM of Cu@Viscose and 3MT@Cu@Viscose
×
Stability and degradation behavior at extreme temperatures
Thermogravimetric analysis is used to study the stability of samples at elevated temperatures and their degradation behavior at extreme temperatures. As shown in Fig. 6, the mass loss observed in all samples below 100 °C is attributed to the evaporation of water. Combining the DTG curve and Table 3, it can be seen that the samples modified with 3MT exhibit a lower initial degradation temperature and maximum degradation temperature. This may be due to the fact that the modification was carried out in a lower pH and heated environment, and it is well-known that cellulose-based materials are prone to acid hydrolysis in acidic conditions, thereby reducing their thermal stability.
Fig. 6
Thermal property of original viscose, 3MT@Viscose, Cu@Viscose and 3MT@Cu@Viscose
Table 3
Degradation temperatures and residue content of samples
Samples
Initial decomposition temperature (°C)
Residue content (%)
Maximum decomposition temperature (°C)
Residue content (%)
Viscose
290
81
339
48
3MT@Viscose
231
93
287
347
82
68
Cu@Viscose
313
82
343
55
3MT@Cu@Viscose
216
94
315
76
×
Interestingly, from the DTG curve, it is observed that the 3MT@Viscose sample exhibits two distinct degradation temperatures. The first stage of degradation may be attributed to the depolymerization, dehydration, and decomposition of cellulose sugar units. The second stage of degradation may be related to the thermal degradation of grafted 3MT molecules, leading to the formation of silicon roots.
It is worth noting that there is a significant change in the residual mass of the materials after 3MT modification and copper plating. First, the 3MT@Viscose sample exhibits a residual mass of approximately 40% at 600 °C. This could be due to the high bond energy of the Si–O–Si chains of 3MT molecules and their uniform dispersion on viscose, effectively acting as a barrier to limit the thermal decomposition of the material. In some studies (Huang et al. 2020; Kim et al. 2022)), 3MT has been used as a reagent to enhance the thermal stability of materials, and their results indicate that the residual mass of the materials is higher after 3MT modification compared to the original samples. However, it should be noted that these studies used carbon materials with excellent chemical resistance, and their thermal degradation temperatures did not significantly change even under harsh conditions.
In this study, in contrast to unmodified copper-plated viscose, the residual mass of 3MT@Cu@Viscose at 600 °C is approximately 60%, significantly higher than Cu@Viscose (27%). This suggests that thiol modification can greatly enhance the electroplating efficiency of copper and form complexes with more copper ions.
Surface and volume resistivity of copper coated samples
Figure 7a presents surface and volume resistivity. The surface and volume resistivity of 3MT@Cu@Viscose is 346.6 and 333.2 mΩ·m, respectively. It is much lower than the surface and volume resistivity (2.4 kΩ and 3.6 kΩ·m) of Cu@Viscose. Combined with the morphology, the copper particles almost completely covered the viscose fiber, endowing 3MT@Cu@Viscose with excellent conductive continuity and greatly reducing its surface and volume resistivity. This may be because, after 3MT modification, SH groups are grafted on the surface of the viscose, which has a strong complexing effect with metal particles. Copper particles are more easily deposited on the surface of the adhesive and penetrate into the network, resulting in extremely low electrical resistance.
Fig. 7
a Surface and volume resistivity of Cu@Viscose and 3MT@Cu@Viscose; b Relative resistance change as a function of bend angle and the number of bends
×
Figure 7b shows the resistance changes of the two samples under bending at different angles and 180° repeated bending. Results showed that 3MT@Cu@Viscose exhibited amazing resistance stability, and its resistance change rate was less than 10%, which is almost negligible when the bending angle was 160°. At the same time, after 500 times of 180° bending, the resistance change rate was still less than 20%, showing excellent flexibility and stability of resistivity. On the contrary, changes in resistance of Cu@Viscose varied greatly and were extremely unstable. This may be attributed to the presence of a large number of SH groups on the surface of the 3MT-modified viscose, which forms a stable coordination complex with metal copper ions to ensure that the copper particles do not fall off during repeated bending. In addition, the durability properties of the samples such as friction resistance (Fig. S2), water washing resistance (Fig. S2S2), oxidation tendency (Fig. S3) and mechanical property (Fig. S4) can be found in the supplementary material. In short, although 3MT modification greatly improves the copper plating performance, it also makes the fabric fragile and has poor physical properties.
Joule heating properties of copper coated samples
As a fabric, it has application potential in future smart clothing, home furnishing, and construction, especially in extreme conditions that require functions such as defogging, defrosting, and heating. We also explored the behavior of Cu@Viscose and 3MT@Cu@Viscose in Joule heating; as shown in Fig. 8a, good electrical conductivity endows excellent Joule heating performance. Joule's law (\({\text{Q}}=\frac{{U}^{2}}{R}t\)) states that heat generated (Q) is proportional to the product of applied voltage (U), sample resistance (R), and operating time (t). Therefore, samples with lower surface resistivity exhibit significantly greater Joule heating performance. In our tests, the modified copper-coated conductive viscose fabric can reach up to 114 °C at a very low voltage (1 V), which is much smaller than the safe voltage of the human body. Moreover, the heating process accomplished a high level within just 10 s, indicating its rapid thermal response time. Similarly, the surface temperature of the fabric decreased quickly in 5 s following power-off, which indicated excellent controllability. As shown in Fig. 8b, the Joule heating performance of 3MT@Cu@Viscose is still very good, even in the bent or twisted state, showing good conductive stability. It may be attributed to the fact that thiol modification significantly enhances the deposition of copper ions during the copper plating process, leading to the accumulation of a sufficient quantity of copper particles on the surface of the viscose. Even when subjected to bending or twisting, the continuity of interconnection between the copper particles can still be maintained.
Fig. 8
a Joule heating performance of Cu@Viscose and 3MT@Cu@Viscose in different voltage; b Joule heating performance of 3MT@Cu@Viscose in bent and twisted states under 1 V
×
Anti-corrosion properties of copper coated samples
By scanning Cu@Viscose and 3MT@Cu@Viscose through potentiodynamic polarization, we observed that the potential of 3MT@Cu@Viscose shifted towards the positive direction, while the polarization current of both the cathode and anode slightly increased in Fig. 9. This suggests that the corrosion resistance of 3MT@Cu@Viscose is better than that of unmodified copper-coated viscose. In order to get more accurate conclusions, we calculated the anode and cathode Tafel slopes (βa and βc), corrosion potential (Ecorr) and corrosion current density (Icorr) and corrosion rate by Tafel analysis, as shown in the Table 4. Through the parameters calculated by the Tafel curve, it can be clearly found that the corrosion potential of 3MT@Cu@Viscose has increased by 72 mV, the corrosion current has decreased by about 5.2 µA/cm2, and the corrosion rate is significantly lower than that of unmodified copper-plated adhesive (about 58% lower). This observation could be attributed to the structure of copper particles deposited on the viscose surface. As previously discussed, the surface of modified copper-plated viscose fibers was almost entirely covered by compact copper particles. This structure provides more complex and tortuous paths for Cl− in the electrolyte to penetrate and diffuse copper ions on the surface, ultimately reducing the corrosion rate (Raza et al. 2018; Chen et al. 2021, 2022). On the other hand, we have confirmed by FTIR that the modified copper-coated viscose forms a Si–O–Si network. It may reduce the hydrophilicity of the conductive fabric, reduce the contact area between the electrolyte and the copper surface, thus improving the corrosion resistance performance (Raza et al. 2018).
Fig. 9
Potentiodynamic polarization curves of Cu@Viscose and 3MT@Cu@Viscose
Table 4
Tafel`s analysis
Sample
βa (mV)
βc (mV)
Ecorr (mV)
Icorr (µA/cm2)
Corrosion rate (mpy)
3MT@Cu@Viscose
70.253
17.646
−133.61
3.809
0.045
Cu@Viscose
284.17
210.41
−205.66
9.012
0.106
×
Shielding properties of copper coated samples
As electronic and electrical products and technologies become increasingly popular, the electromagnetic pollution generated by EMI can have adverse effects on nearby electronic and electrical equipment, as well as organisms. Therefore, it is crucial to develop shielding materials that can effectively absorb or reflect radiation in order to eliminate or suppress these EMI effects.
In this study, we evaluated the EMI shielding performance of the samples across a frequency range of 30 MHz–3 GHz, which encompasses various civilian applications such as radio broadcasting, mobile communication, TV FM, wireless LAN, radar, GPS, and more. From the Fig. 10, we can clearly observe that the EMI shielding effectiveness of 3MT@Cu@Viscose is 55–60 dB at each frequency and 56.6 dB in average value, indicating that about at least 99.9% of the electromagnetics were reflected or absorbed by 3MT@Cu@Viscose, while that of Cu@Viscose is less than 10 dB (only 70–90% of the electromagnetics were reflected or absorbed). Furthermore, we discovered that the EMI shielding mechanism for both samples is primarily dominated by reflection, which is the primary mechanism for electromagnetic shielding on most metal surfaces. When electromagnetic waves reach the surface of the conductive fabric, the majority of them are initially reflected due to the large number of free electrons (impedance mismatch) on the conductive metal network surface (Maruthi et al. 2021). Any remaining waves then penetrate and interact with the copper lattices, where their high electron density induces ohmic losses and interfacial polarization losses, resulting in a reduction in wave energy (Jia et al. 2022).
Fig. 10
EMI shielding effectiveness of samples in the 30 MHz–3 GHz band
×
Conclusion
In this work, the successfully developed a conductive modified viscose fabric that exhibits multiple functions was presented. FTIR analysis confirmed the presence of SH groups grafted onto the surface of the prepared samples. In surface morphology tests, the modified viscose fibers were almost entirely covered by dense and firm copper particles, which showed strong complexation with copper ions during the copper plating process. Additionally, the residual mass of 3MT@Cu@Viscose from TGA measurements confirmed that the modified viscose fabric had a stronger affinity for copper ions, which promoted more efficient copper ion deposition. Tafel`s analysis confirmed that the corrosion rate of 3MT@Cu@Viscose is about 58% lower than that of unmodified Cu@Viscose, which greatly improves the stability and durability of the composite. 3MT@Cu@Viscose also showed extremely low surface and volume resistivity (346.6 mΩ and 333.2 mΩ·m) and after 500 times of repeated bending, the resistivity change rate is still in a low state (< 20%). Due to its excellent electrical conductivity, 3MT@Cu@Viscose achieved Joule heating performance with a fast response at extremely low voltage (1 V) and excellent EMI shielding effectiveness.
Acknowledgments
This work was supported by the research project of Student Grant Competition of Technical University of Liberec no. 2023-6374 granted by Ministry of Education Youth and Sports of Czech Republic.
Declarations
Conflict of interest
We have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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Ethical approval
Manuscripts reporting studies that do not involve human participants, human data, or human tissue.
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