Resistance against Penetration of Electromagnetic Radiation for Ultra-light Cu/Ni-Coated Polyester Fibrous Materials

Resistance against penetration of various rays including electromagnetic waves (EM), infrared rays (IR), and ultraviolet rays (UV) has been realized by using copper (Cu)-coated fabrics. However, the corrosion of the Cu on coated fabrics influenced the shielding effectiveness of the various rays. Besides, the metal-coated fabrics have high density and are unbreathable. This work aims to solve the problem by incorporating nickel (Ni) into the Cu coating on the ultra-light polyester fibrous materials (Milife® composite nonwoven fabric—10 g/m2, abbreviation Milife) via electroless plating. The electromagnetic interference (EMI), IR test, ultraviolet protection factor (UPF), water contact angle, and air permeability of the Cu/Ni-coated Milife fabric were measured. All the samples were assumed as ultra-light and breathable by obtaining the similar fabric density (~10.57 g/m2) and large air permeability (600–1050 mm/s). The Cu/Ni deposition on the Milife fabrics only covered the fibers. The EM shielding effectiveness (SE) decreased from 26 to 20 dB, the IR reflectance (Rinfrared) decreased from 0.570 to 0.473 with increasing wNi from 0 to 19.5 wt %, while the wNi improved the UPF from 9 to 48. Besides, addition of Ni changed the Cu/Ni-coated Milife fabric from hydrophilicity to the hydrophobicity by observing WCA from 77.7° to 114°.


Introduction
Currently, electromagnetic pollution has increased rapidly because of the rapid growth of smartphone, wireless, and utilization of other electronic devices [1]. Generally, these equipment's emits the electromagnetic energy with respect to the different frequency which causes serious concerns to the exposed human body [2]. For example, Singh et al. [3] revealed that a majority of the subjects who were residing near the mobile base station complain of sleep disturbances, headache, dizziness, irritability, concentration difficulties, and hypertension. Besides, the possibility of the leakage of personal information from electronic devices via the near field communication (NFC) technology also exist [4]. To protect electrical equipment and human body from these damages, electromagnetic interference (EMI) shielding provides a solution. Shielding of electromagnetic waves is here achieved by the absorption and reflection of electromagnetic (EM) radiation in the metal-coated fabrics and its shielding effectiveness (SE) is given to the evaluate the EMI level [5]. To achieve this goal, the metal-deposited fabrics with enhanced electromagnetic shielding are considered.

•
Precleaning and surface structure opening: Pre-cleaning process on Milife fabric was carried out by using 2.5% non-ionic detergent (Noigen LV-4) with temperature of 40 • C. This process was kept at pH of 7 and duration was 20 min. The pre-cleaned fabric was rinsed with deionized water for the effective removal of residual surfactants. Surface structure opening was realized by hydrolytic treatment of the fabric in 1% sodium hydroxide (NaOH) at 70 • C for 5 min with subsequent rinsing in demineralized water. • Surface activation process was carried out by using an activation solution (CATAPOSIT44, produced by Rohm and Hass Company, Amsterdam, Netherlands) at 45 • C for 5 min, following which the pretreated Milife fabric was immersed in 10% hydrochloric acid (HCl) for 1 min. The demineralized water was used to wash the activated fabric.

•
Deposition of Cu/Ni on the Milife fabric during plating was realized in a mixture of copper (CuSO 4 ·5H2O) and nickel sulphate (NiSO 4 ·6H 2 O) in weight ratio of 1:1 in the presence of triethanolamine (TEA). After depositing the Milife fabric in the mixture, homogeneous generation and deposition of Cu-Ni alloy nanocrystals was performed by metering a solution of sodium borohydride (NaBH 4 ) in volume ratio of 1:1 into this mixture without access of air at temperature 22 • C. Composition and concentration of the solutions were the same for all samples, following the ratio like 1. 3 g CuSO 4 ·5H 2 O, 3 g NiSO 4 ·6H 2 O, 14 g TEA, 0,5 g NaBH 4 , and 1 g NaOH per liter. The pH of the prepared solution was 9.5. After deposition, the 2× subsequent rinsing in demineralized water was done.
During the preparation process, all the chemicals were used for the measurement without further modification.
To observe the effect of Ni on the properties of Cu/Ni-coated Milife fabric, eight samples were prepared by controlling the Ni weight percentage in the electroless plating process from 0 to 25 wt % (details in Table 1). The Ni weight percentage was expressed in relation to the weight content of NiSO 4 ·6H 2 O of the total weight content of CuSO 4 ·5H 2 O and NiSO 4 ·6H 2 O in the chemical plating bath. Concentration of Ni and Cu in chemical plating bath were directly evaluated analytically by standard atomic absorption spectroscopy (AAS) method. The AAS was also used for determination of content of Ni and Cu on the surface of platted fabrics after quantitative dissolution in 35 wt % nitric acid, and the results are given in Table 1. Besides, the pure Milife fabric was used as control sample and labeled as N0.

Morphology and Structural Analysis
The surface morphology of Milife fabric with and without Cu/Ni coating was observed under the scanning electron microscopy (SEM) (VEGA TESCAN Inc., Licoln, NE, USA) at 20 kV. The cross-section and the surface of the Cu/Ni-coated fabric were tested.
Air permeability of Milife fabric with and without Cu/Ni-coating was measured by the machine FX3300 under 100 Pa according to ISO 9237.

Electromagnetic Shielding Effectiveness (EM SE)
Electromagnetic shielding effectiveness (EM SE) was analyzed by using a device described in Šafářová et al.'s work [21] in accordance with ASTM D4935-10. During the measurement, temperature was kept at 27 ± 1 • C and relative humidity was kept at 40 ± 1%. EM SE of Cu/Ni-coated sample was measured over frequency range of 30 MHz to 1.5 GHz and the results were expressed in decibels (dB). The set-up consisted of a sample holder with its input and output connected to the network analyzer. A shielding effectiveness test fixture (Electro-Metrics, Inc., Johnstown, NY, USA, model EM-2107A) was used to hold the sample. The design and dimension of sample holder followed the ASTM method mentioned above. Network analyzer Rohde & Schwarz ZN3 was used to generate and receive the electromagnetic signals. The standard mentioned above determined the electromagnetic shielding effectiveness of the fabric using the insertion-loss method. The set-up of the instrument was well explained in the previous research manuscripts from our laboratory [22,23]. The set-up consisting of the distribution of electrical and magnetic fields were in the coaxial transmission. Before EM SE measurements, the instrument was calibrated. Ten repetitive measurements were conducted, and statistical analysis was done. From the tests, the SE and reflection loss (SE R ) were obtained.
Here, SE-shielding effectiveness, SE R -reflection loss, SE A -absorption loss, SE M -re-reflection correction factor. Normally, SE M can be neglected. So SE A can be calculated according to Equation (1).
According to the Equations (2) and (3), the transmittance (T EM ) and reflectance (R EM ) can be calculated. Absorptance (A EM ) can be obtained by Equation (4). In addition, the EMI value at 1.5 GHz was used to calculate the reflection loss (R EM ), transmission loss (T EM ), effective absorbance (A eff,EM ), and the emissivity (E m,EM ) according to the Equations (4)- (7).

Electrical Conductivity
Surface resistance (ρ s ) of the Cu/Ni-coated samples was measured by using concentric electrodes (applied pressure 2.3 kPa) under a 100 V direct current (DC) power (Figure 1), in accordance with ATSM D257-07 standard. During the test, the electrodes were placed on the sample for 60 s and then surface resistivity values (ρ s ) were recorded. All samples were placed in the air-conditioned room 24 h prior to testing and the measurement was carried out with the temperature of 21 • C and the relative humidity (RH) was 45%.

Spectral Reflectance Evaluation
The spectral reflectance (R infrared ) ranging from 2 to 20 µm (500-5000 cm −1 ) of textiles was tested by using the integration ball principle on the Mid-IR IntegratIR ™ (PIKE Technologies ™) ( Figure 2). The beam stroked the specimen at an angle of 8 • and interacted with its surface. The reflected radiation component was further diffusively reflected from the surface of the integration ball, and its value for individual wavelengths was recorded on a nitrogen-cooled measurement sensor. Besides, the spectral transmittance (T infrared ) was also measured. Similar as the evaluation on the EM SE of the Cu/Ni-coated Milife fabrics (Section 2.3.2), the infrared curves of all the samples were calculated according to Equation (4), and the infrared absorbance (A infrared ) was also obtained.

Electrical Conductivity
Surface resistance ( ) of the Cu/Ni-coated samples was measured by using concentric electrodes (applied pressure 2.3 kPa) under a 100 V direct current (DC) power (Figure 1), in accordance with ATSM D257-07 standard. During the test, the electrodes were placed on the sample for 60 s and then surface resistivity values ( ) were recorded. All samples were placed in the air-conditioned room 24 h prior to testing and the measurement was carried out with the temperature of 21 °C and the relative humidity (RH) was 45%.

Spectral Reflectance Evaluation
The spectral reflectance (Rinfrared) ranging from 2 to 20 μm (500-5000 cm −1 ) of textiles was tested by using the integration ball principle on the Mid-IR IntegratIR ™ (PIKE Technologies ™) ( Figure 2). The beam stroked the specimen at an angle of 8° and interacted with its surface. The reflected radiation component was further diffusively reflected from the surface of the integration ball, and its value for individual wavelengths was recorded on a nitrogen-cooled measurement sensor. Besides, the spectral transmittance (Tinfrared) was also measured. Similar as the evaluation on the EM SE of the Cu/Ni-coated Milife fabrics (Section 2.3.2), the infrared curves of all the samples were calculated according to Equation (4), and the infrared absorbance (Ainfrared) was also obtained.
In addition, the IR values at 1000 cm −1 were focused. Both infrared emissitivty (Em,infrared) and infrared effective absorbance (Aeff,infrared) were obtained as well by using the Equation (7) and (5) separately. Furthermore, the functional group of the Cu/Ni-coated Milife fabrics were characterized from the Ainfrared and Tinfrared curves. The temperature of the spectral measurement was kept 20 ± 1 °C by using the nitrogen (N2) gas. It was noticeable that the real thermal radiation reflection of the fabric was affected by the air property (speed, temperature, components,…). Especially, the porosity of the fabric also influences the thermal radiation reflection. Therefore, a custom-built set-up ( Figure 3) was used to observe the temperature different between the heating source and the surface of the sample. The thin cotton fabric ( = 0.95) attached on the heater source was used as thermal radiation surface and its temperature was set as 313.15 K (Th). The sample to be measured was placed at a distance 30 mm (L) from the thermal radiation surface. After 10 min, the temperature of the sample (Ts) was recorded by K type thermo sensor connected with a temperature recorder (VOLFCRAFT IR 1201 50D). Besides, the thermal radiation surface and the measured sample were confined in a sealed space 1 ( = 0.95). To avoid the thermal convection, the sealed space 2 ( = 0.95) was set to enclose the aforementioned elements and its temperature (Tsur) was around 298.15 K. Here, was the emissivity.  In addition, the IR values at 1000 cm −1 were focused. Both infrared emissitivty (E m,infrared ) and infrared effective absorbance (A eff,infrared ) were obtained as well by using the Equations (7) and (5) separately. Furthermore, the functional group of the Cu/Ni-coated Milife fabrics were characterized from the A infrared and T infrared curves. The temperature of the spectral measurement was kept 20 ± 1 • C by using the nitrogen (N 2 ) gas.
It was noticeable that the real thermal radiation reflection of the fabric was affected by the air property (speed, temperature, components, . . . ). Especially, the porosity of the fabric also influences the thermal radiation reflection. Therefore, a custom-built set-up ( Figure 3) was used to observe the temperature different between the heating source and the surface of the sample. The thin cotton fabric ( rad = 0.95) attached on the heater source was used as thermal radiation surface and its temperature was set as 313.15 K (T h ). The sample to be measured was placed at a distance 30 mm (L) from the thermal radiation surface. After 10 min, the temperature of the sample (T s ) was recorded by K type thermo sensor connected with a temperature recorder (VOLFCRAFT IR 1201 50D). Besides, the thermal radiation surface and the measured sample were confined in a sealed space 1 ( wall1 = 0.95). To avoid the thermal convection, the sealed space 2 ( wall2 = 0.95) was set to enclose the aforementioned elements and its temperature (T sur ) was around 298.15 K. Here, was the emissivity.

Ultraviolet Protection
The ultraviolet (UV) protection of the Cu/Ni-coated Milife fabrics was performed by using the Shimadzu UV 31001 PC ultraviolet-visiable (UV-Vis) Spectrophotometer with the spectral wavelength from 290 to 400 nm. The ultraviolet protection factor (UPF) value was calculated by using the following Equation (8). where, S λ is the irradiance of solar spectrum, E λ is the relative erythemal spectral response, T λ is the average spectral transmittance of the sample, and ∆λ is the measured wavelength interval in nanometers.
property (speed, temperature, components,…). Especially, the porosity of the fabric also influences the thermal radiation reflection. Therefore, a custom-built set-up ( Figure 3) was used to observe the temperature different between the heating source and the surface of the sample. The thin cotton fabric ( = 0.95) attached on the heater source was used as thermal radiation surface and its temperature was set as 313.15 K (Th). The sample to be measured was placed at a distance 30 mm (L) from the thermal radiation surface. After 10 min, the temperature of the sample (Ts) was recorded by K type thermo sensor connected with a temperature recorder (VOLFCRAFT IR 1201 50D). Besides, the thermal radiation surface and the measured sample were confined in a sealed space 1 ( = 0.95). To avoid the thermal convection, the sealed space 2 ( = 0.95) was set to enclose the aforementioned elements and its temperature (Tsur) was around 298.15 K. Here, was the emissivity.

Water Contact Angle
Water contact angle for the Cu/Ni-coated Milife fabric was analyzed according to sessile drop principle by using the surface energy evaluation analyzer (Advex Instruments dependent on ISO: 27448:2009, Czech Republic). Deionized water was used for the contact angle measurement as a testing liquid. Total of 5 µL was used as the volume of testing liquid for all the measurement. In the measurement, the 5 µL of deionized water was dropped on the surface of Cu/Ni-coated Milife fabric by using micro syringe, and after 2 min the water contact angle was recorded. It was repeated ten times with different Cu/Ni-coated Milife fabric and the ten values were averaged.

Morphology and Structural Analysis
The surface of Milife fabric with and without Cu/Ni-coating was observed from SEM images (Figures 4 and 5). Control samples have plain surface without any metal addition, whereas the samples coated with Ni showed the deposition of metal particles on the surface. It was interesting to observe that the deposited Cu/Ni were on the surface of the fibers and did not fill in the interspace between the fibers significantly.
The structural change between the Milife fabric with and without Cu/Ni-coating is shown in Figure 6. It was found that Cu/Ni coating layer was very thin. It was also found that the Cu/Ni coating amount could be assumed as almost same (Table 1) and ranges from 0.47 to 0.60 g/m 2 . Therefore, the Cu/Ni-coated Milife fabric had the GSM ranging from 10.47 to 10.60 g/m 2 , which supported that the prepared samples were light.
Polymers 2020, 12, x FOR PEER REVIEW 6 of 16 The ultraviolet (UV) protection of the Cu/Ni-coated Milife fabrics was performed by using the Shimadzu UV 31001 PC ultraviolet-visiable (UV-Vis) Spectrophotometer with the spectral wavelength from 290 to 400 nm. The ultraviolet protection factor (UPF) value was calculated by using the following Equation (8).
where, Sλ is the irradiance of solar spectrum, Eλ is the relative erythemal spectral response, Tλ is the average spectral transmittance of the sample, and Δλ is the measured wavelength interval in nanometers.

Water Contact Angle
Water contact angle for the Cu/Ni-coated Milife fabric was analyzed according to sessile drop principle by using the surface energy evaluation analyzer (Advex Instruments dependent on ISO: 27448: 2009, Czech Republic). Deionized water was used for the contact angle measurement as a testing liquid. Total of 5 μL was used as the volume of testing liquid for all the measurement. In the measurement, the 5 μL of deionized water was dropped on the surface of Cu/Ni-coated Milife fabric by using micro syringe, and after 2 min the water contact angle was recorded. It was repeated ten times with different Cu/Ni-coated Milife fabric and the ten values were averaged.

Morphology and Structural Analysis
The surface of Milife fabric with and without Cu/Ni-coating was observed from SEM images (Figures 4 and 5). Control samples have plain surface without any metal addition, whereas the samples coated with Ni showed the deposition of metal particles on the surface. It was interesting to observe that the deposited Cu/Ni were on the surface of the fibers and did not fill in the interspace between the fibers significantly.
The structural change between the Milife fabric with and without Cu/Ni-coating is shown in Figure 6. It was found that Cu/Ni coating layer was very thin. It was also found that the Cu/Ni coating amount could be assumed as almost same (Table 1) and ranges from 0.47 to 0.60 g/m 2 . Therefore, the Cu/Ni-coated Milife fabric had the GSM ranging from 10.47 to 10.60 g/m 2 , which supported that the prepared samples were light.
The air permeability of the Milife fabrics with Cu/Ni deposition (N1-N8) was slightly smaller than the Milife fabric (N0). There was no obvious difference in the air permeability between N1, N2, N3, N4, N5, N6, and N7 by observing the value ranging from 700 to 1000 mm/s, while the air permeability of the sample (N8) was significantly decreased to 600 mm/s ( Figure 7). The difference may be caused by different Cu/Ni crystals on the surface of the fiber. Overall, the high air permeability (>600 mm/s) supported the breathability of the Cu/Ni-coated Milife fabric by comparing with other work [24,25].

Effect of Ni Content in the Cu/Ni-Coating Milife Fabric on EMI
EMI results including EM SE and SER with frequency ranging from 30M-1.5G are shown in Figure 8, and the evaluation of the EMI is calculated in the Table 2.
From the Figure 8A, it was found that the EM SE was obtained when there was Cu/Ni deposition on the Milife fabric since only the N0 (without Cu/Ni deposition) had the EM SE around 0 dB. The sample N1 (only with Cu deposition) was assumed the highest EM SE by observing the highest EM SE curve and the other samples N2-N8 (Cu/Ni-coated Milife fabrics) had the lower EM SE than the sample N1, which meant that the addition of Ni in the Cu coating on Milife fabric reduced the EM SE. The EM SE of the Cu/Ni-coated Milife fabric at 1.5 G decreased from 26.87 to 19.77 dB with the increasing wNi ( Table 2). The linear relationship between the wNi and the EM SE was modeled in the Figure 8B, and R 2 = 0.97. In addition, it was found that the effect of wNi on the SER was not as significant as on the EM SE, which was proved by the close SER curves shown in Figure 8C. The SER at 1.5 G of the Cu/Ni-coated Milife fabric increased from 14.67 to 15.22 dB with the increasing wNi ( Table 2).
The trend of the EM SE and SER of the Cu/Ni-coated Milife fabric over the wNi was different, which suggested the EMI mechanism was affected by the wNi. It was well-known that the EM wave

Effect of Ni Content in the Cu/Ni-Coating Milife Fabric on EMI
EMI results including EM SE and SER with frequency ranging from 30M-1.5G are shown in Figure 8, and the evaluation of the EMI is calculated in the Table 2.
From the Figure 8A, it was found that the EM SE was obtained when there was Cu/Ni deposition on the Milife fabric since only the N0 (without Cu/Ni deposition) had the EM SE around 0 dB. The sample N1 (only with Cu deposition) was assumed the highest EM SE by observing the highest EM SE curve and the other samples N2-N8 (Cu/Ni-coated Milife fabrics) had the lower EM SE than the sample N1, which meant that the addition of Ni in the Cu coating on Milife fabric reduced the EM SE. The EM SE of the Cu/Ni-coated Milife fabric at 1.5 G decreased from 26.87 to 19.77 dB with the increasing wNi ( Table 2). The linear relationship between the wNi and the EM SE was modeled in the Figure 8B, and R 2 = 0.97. In addition, it was found that the effect of wNi on the SER was not as significant as on the EM SE, which was proved by the close SER curves shown in Figure 8C. The SER at 1.5 G of the Cu/Ni-coated Milife fabric increased from 14.67 to 15.22 dB with the increasing wNi ( Table 2).
The trend of the EM SE and SER of the Cu/Ni-coated Milife fabric over the wNi was different, which suggested the EMI mechanism was affected by the wNi. It was well-known that the EM wave The air permeability of the Milife fabrics with Cu/Ni deposition (N1-N8) was slightly smaller than the Milife fabric (N0). There was no obvious difference in the air permeability between N1, N2, N3, N4, N5, N6, and N7 by observing the value ranging from 700 to 1000 mm/s, while the air permeability of the sample (N8) was significantly decreased to 600 mm/s (Figure 7). The difference may be caused by different Cu/Ni crystals on the surface of the fiber. Overall, the high air permeability (>600 mm/s) supported the breathability of the Cu/Ni-coated Milife fabric by comparing with other work [24,25].

Effect of Ni Content in the Cu/Ni-Coating Milife Fabric on EMI
EMI results including EM SE and SER with frequency ranging from 30M-1.5G are shown in Figure 8, and the evaluation of the EMI is calculated in the Table 2.
From the Figure 8A, it was found that the EM SE was obtained when there was Cu/Ni deposition on the Milife fabric since only the N0 (without Cu/Ni deposition) had the EM SE around 0 dB. The sample N1 (only with Cu deposition) was assumed the highest EM SE by observing the highest EM SE curve and the other samples N2-N8 (Cu/Ni-coated Milife fabrics) had the lower EM SE than the sample N1, which meant that the addition of Ni in the Cu coating on Milife fabric reduced the EM SE. The EM SE of the Cu/Ni-coated Milife fabric at 1.5 G decreased from 26.87 to 19.77 dB with the increasing wNi ( Table 2). The linear relationship between the wNi and the EM SE was modeled in the Figure 8B, and R 2 = 0.97. In addition, it was found that the effect of wNi on the SER was not as significant as on the EM SE, which was proved by the close SER curves shown in Figure 8C. The SER at 1.5 G of the Cu/Ni-coated Milife fabric increased from 14.67 to 15.22 dB with the increasing wNi (Table 2).

Effect of Ni Content in the Cu/Ni-Coating Milife Fabric on EMI
EMI results including EM SE and SE R with frequency ranging from 30 M-1.5 G are shown in Figure 8, and the evaluation of the EMI is calculated in the Table 2. good" category for general use (Table 4).
Furthermore, the EM SE was in relation to the surface resistivity ( ). As shown in Table 5, the of all the Cu/Ni-coated Milife fabrics (N1-N8) were smaller than 60 Ω/sq while the of the pure Milife fabric was as large as 13.45 M Ω . The Cu/Ni deposition gave the Milife fabric the good conductivity. Besides, no linear relationship between and wNi was found. The wNi did not change the surface electrical conductivity of the Cu/Ni coating on the Milife fabric.     From the Figure 8A, it was found that the EM SE was obtained when there was Cu/Ni deposition on the Milife fabric since only the N0 (without Cu/Ni deposition) had the EM SE around 0 dB. The sample N1 (only with Cu deposition) was assumed the highest EM SE by observing the highest EM SE curve and the other samples N2-N8 (Cu/Ni-coated Milife fabrics) had the lower EM SE than the sample N1, which meant that the addition of Ni in the Cu coating on Milife fabric reduced the EM SE. The EM SE of the Cu/Ni-coated Milife fabric at 1.5 G decreased from 26.87 to 19.77 dB with the increasing w Ni ( Table 2). The linear relationship between the w Ni and the EM SE was modeled in the Figure 8B, and R 2 = 0.97. In addition, it was found that the effect of w Ni on the SE R was not as significant as on the EM SE, which was proved by the close SE R curves shown in Figure 8C. The SE R at 1.5 G of the Cu/Ni-coated Milife fabric increased from 14.67 to 15.22 dB with the increasing w Ni ( Table 2).
The trend of the EM SE and SE R of the Cu/Ni-coated Milife fabric over the w Ni was different, which suggested the EMI mechanism was affected by the w Ni . It was well-known that the EM wave passing through the Cu/Ni-coated Milife fabric ( Figure 8D) included the reflection SE R , adsorption SE A , and transmittance EM SE. To confirm the exact EMI mechanism in the Cu/Ni-coated Milife fabric, three parts including SE R , SE A , and EM SE at 1.5G were evaluated according to the Equation (2)-(4) and shown in Table 2. It was found that R EM and T EM increased while the A eff,EM and E m,EM decreased. The linear relationship between R EM , T EM , A eff,EM , E m,EM , and w Ni was modeled separately in Figure 8E,F. The details of the relationship are shown in Table 3. The slope of the A eff,EM was much higher than R EM (0.0151 > 0.0002), which suggested that the A eff,EM loss in the Cu/Ni-coated Milife fabric mainly accounted for the decrease of the EM SE. Namely, addition of Ni in the Cu coating on the Milife fabric increased the EMI reflection while seriously reduced the EMI adsorption. Besides, E m,EM of the Cu/Ni-coated Milife fabric linearly decreased from 0.034 to 0.030 with the increased w Ni . Although the Ni had a negative effect on the EM SE of the Cu/Ni-coated Milife fabrics, the EM SE of the samples were above 20 dB except for the sample N8 whose EM SE was around 19 dB. According to the classification, the prepared Cu/Ni-coated Milife fabrics were evaluated in the "very good" category for general use (Table 4). Furthermore, the EM SE was in relation to the surface resistivity (ρ s ). As shown in Table 5, the ρ s of all the Cu/Ni-coated Milife fabrics (N1-N8) were smaller than 60 Ω/sq while the ρ s of the pure Milife fabric was as large as 13.45 MΩ. The Cu/Ni deposition gave the Milife fabric the good conductivity. Besides, no linear relationship between ρ s and w Ni was found. The w Ni did not change the surface electrical conductivity of the Cu/Ni coating on the Milife fabric.

UV Properties of Cu/Ni-Coated Fabric
The UV measurement of Cu/Ni-coated Milife fabric including both of ultraviolet radiation A (UVA) and ultraviolet radiation B (UVB) was shown in Figure 9. It was obvious that UV transmittance percentage of Cu/Ni-coated Milife fabric decreased with higher w Ni over the UV electromagnetic spectrum. The UV transmittance percentage increased significantly in the fabrics N1, N2, N3, N4, and N5, and fabrics N6, N7, and N8 had less than 5% of transmittance all over the UV region (290-400 nm). The stable and good UV protective property was obtained when w Ni was higher than 15.2 wt %.
(UVA) and ultraviolet radiation B (UVB) was shown in Figure 9. It was obvious that UV transmittance percentage of Cu/Ni-coated Milife fabric decreased with higher wNi over the UV electromagnetic spectrum. The UV transmittance percentage increased significantly in the fabrics N1, N2, N3, N4, and N5, and fabrics N6, N7, and N8 had less than 5% of transmittance all over the UV region (290-400 nm). The stable and good UV protective property was obtained when wNi was higher than 15.2 wt %. Figure 10 showed the UV protection capability of Cu/Ni-coated Milife fabric in terms of UPF values. As in sun protection factor (SPF) rating system used in case of sunscreens fabric, UPF rating is used to measure the UV protection [27]. Usually if the UPF value of fabric has equal or more than 50, it can provide the better protection by blocking the 98% of UV radiations. The Cu-coated Milife fabric (N1) had the lowest UPF value around 9, which was assumed to have little UV protective ability as their UPF values are about 8-10 (<15). When the coated fabric contained 2 wt % wNi (N2), the UPF value was 20.2. Similarly, the UPF was increased with the increased wNi. On other hand, the fabric with higher wNi (>7.1 wt %) showed 40+ UPF ratings. The UPF values increased till wNi reached 15.2 wt % and thereafter it was saturated with no significant difference in the UPF values. It was found that the resistance against UV for the Cu/Ni-coated Milife fabric could be modified with increased wNi while the resistance against EMI was reduced with more wNi. The reason may be that the Ni was able to dissipate the electromagnetic energy ranging from 290-400 nm. With respect to the wNi in the coated fabric, 16.6 wt % of Ni in the sample contributed to 46 UPF value and 19.2 wt % of Ni in the sample contributed to 48 UPF value. For statistical approach, we fitted the data between UPF value and wNi by using exponential function (Equation 9), where Uf was set as 50 according to standard stating that excellent protection from UV when UPF was ≥50. Ui was the initial UPF of the Cu-coated Milife fabric (N1). kU was the estimated value giving the increasing rate of UPF with Ni deposition.
kU was estimated as 0.115 and the final fitting model had R 2 = 0.91, which confidently proved that there was an exponential relationship between wNi and UPF value.   Figure 10 showed the UV protection capability of Cu/Ni-coated Milife fabric in terms of UPF values. As in sun protection factor (SPF) rating system used in case of sunscreens fabric, UPF rating is used to measure the UV protection [27]. Usually if the UPF value of fabric has equal or more than 50, it can provide the better protection by blocking the 98% of UV radiations. The Cu-coated Milife fabric (N1) had the lowest UPF value around 9, which was assumed to have little UV protective ability as their UPF values are about 8-10 (<15). When the coated fabric contained 2 wt % w Ni (N2), the UPF value was 20.2. Similarly, the UPF was increased with the increased w Ni . On other hand, the fabric with higher w Ni (>7.1 wt %) showed 40+ UPF ratings. The UPF values increased till w Ni reached 15.2 wt % and thereafter it was saturated with no significant difference in the UPF values. It was found that the resistance against UV for the Cu/Ni-coated Milife fabric could be modified with increased w Ni while the resistance against EMI was reduced with more w Ni . The reason may be that the Ni was able to dissipate the electromagnetic energy ranging from 290-400 nm. With respect to the w Ni in the coated fabric, 16.6 wt % of Ni in the sample contributed to 46 UPF value and 19.2 wt % of Ni in the sample contributed to 48 UPF value. For statistical approach, we fitted the data between UPF value and w Ni by using exponential function (Equation (9)), where U f was set as 50 according to standard stating that excellent protection from UV when UPF was ≥50. U i was the initial UPF of the Cu-coated Milife fabric (N1). k U was the estimated value giving the increasing rate of UPF with Ni deposition.
k U was estimated as 0.115 and the final fitting model had R 2 = 0.91, which confidently proved that there was an exponential relationship between w Ni and UPF value.
Polymers 2020, 12, x FOR PEER REVIEW 11 of 16 Figure 10. The relationship between UPF and wNi.

Infrared Analysis of Cu/Ni-Coated Milife Fabric
The infrared resistance evaluation on Cu/Ni-coated Milife fabric including reflectance (Rinfrared), transmittance (Tinfared) and adsorption (Ainfrared) was schemed in Figure 11 and the values at 1000 cm −1 are shown in Table 6 Ainfrared and Tinfared curves were used to characterize the components of the Cu/Ni-coated Milife fabrics. It was found that all the samples had the same peaks in the Ainfrared except for the peak ranging from 2360 to 2340 cm −1 ( Figure 11A). The ester groups of all the samples were proved by observing the strong peaks at 1712,1090, and 1244 cm −1 separately. The peaks in the range between 1712 to 1627 cm −1 and 1555 to 1425 cm −1 confirmed that there was a deposition of Cu and Ni particles on the surface of Milife fabric [20]. The peak at 3430 cm −1 represented the -OH group, which suggested that the hydrolysis and aminolysis happened during the electroless plating process and the strong interaction between metal particles and polyester was developed. However, the peaks of the samples ranging from 2360 to 2340 cm −1 were different, which represented the stretching and vibration of -C=N=O-or -N=C=O-. It was found that the peaks from 2360 to 2340 cm −1 became stronger with higher wNi (> 4.8 wt%). It may be caused by the unstable coating process when the higher Ni molar was introduced in the electroless plating process, and the balance between the chemical reaction was affected. For the Tinfared curves ( Figure 11B), only the peaks ranging from 2360 to 2340 cm −1 were changed until the wNi was higher than 8.8 wt %.
Rinfrared values were used to evaluate the resistance of the Cu/Ni-coated Milife fabric against penetration of IR. As seen in Figure 11C, all the samples had a similar Rinfrared curve over the wave number from 516 to 5000 cm −1 by observing the same peak position and the similar increasing trend that Rinfrared values increased with decreasing wave number and tended to be stable after the 1000 cm −1 . The Rinfrared at 1000 cm −1 of different samples were different which proved that the wNi affected the Rinfrared. By observing the Rinfrared at 1000 cm −1 over the wNi ( Figure 11C and Table 6), it was found that no obvious decrease of Rinfrared happened until the wNi reached 5.5 wt %, and the Rinfrared tended to be saturated when the wNi reached 16.6 wt %. Therefore, the influence of the wNi on the Rinfrared was considered to be classified into two stages: the stable stage (I: wNi < 5.5 wt % and II: wNi > 16.6 wt %) and the negative stage (5.5 wt % < wNi < 16.6 wt %) ( Figure 11C). On the one hand, the initial Rinfrared was measured around 0.57 in the stable stage I and the lowest Rinfrared was measured around 0.473 in Figure 10. The relationship between UPF and w Ni.

Infrared Analysis of Cu/Ni-Coated Milife Fabric
The infrared resistance evaluation on Cu/Ni-coated Milife fabric including reflectance (R infrared ), transmittance (T infared ) and adsorption (A infrared ) was schemed in Figure 11 and the values at 1000 cm −1 are shown in Table 6. Table 6. Evaluation of infrared resistance of Cu/Ni-coated Milife Fabric at 1000 (cm −1 ). A infrared and T infared curves were used to characterize the components of the Cu/Ni-coated Milife fabrics. It was found that all the samples had the same peaks in the A infrared except for the peak ranging from 2360 to 2340 cm −1 ( Figure 11A). The ester groups of all the samples were proved by observing the strong peaks at 1712, 1090, and 1244 cm −1 separately. The peaks in the range between 1712 to 1627 cm −1 and 1555 to 1425 cm −1 confirmed that there was a deposition of Cu and Ni particles on the surface of Milife fabric [20]. The peak at 3430 cm −1 represented the -OH group, which suggested that the hydrolysis and aminolysis happened during the electroless plating process and the strong interaction between metal particles and polyester was developed. However, the peaks of the samples ranging from 2360 to 2340 cm −1 were different, which represented the stretching and vibration of -C=N=O-or -N=C=O-. It was found that the peaks from 2360 to 2340 cm −1 became stronger with higher w Ni (>4.8 wt %). It may be caused by the unstable coating process when the higher Ni molar was introduced in the electroless plating process, and the balance between the chemical reaction was affected. For the T infared curves ( Figure 11B), only the peaks ranging from 2360 to 2340 cm −1 were changed until the w Ni was higher than 8.8 wt %.

Sample Code
Furthermore, the practical testing of the Cu/Ni-coated Milife fabrics for the thermal radiation resistance was carried out according to Section 2.3.4. The results are shown in Table 7. All the samples had the much lower Ts (302-304K) than the Th (313.15K). In addition, a small decrease was observed by comparing the samples with Ni (N2-N8) with Cu-coated Milife fabric (N1), while there was no similar linear relationship between the Ts and wNi, which was different from the aforementioned standard IR resistance analysis. The phenomena may be caused by the higher porosity of the samples, where the infrared transmittance and the unexpectable heat convection existed during the measurement. The change of the air components in the measurement also accounted for the difference as well.
Furthermore, by combining the results of the EMI and UV with the IR analysis, it was found that the addition of Ni only had a positive influence in the resistance against the penetration of electromagnetic waves when the wavelength only ranged from 290 to 400 nm in this case. Namely, the Ni had the selectivity on the resistance against the penetration of electromagnetic waves.   R infrared values were used to evaluate the resistance of the Cu/Ni-coated Milife fabric against penetration of IR. As seen in Figure 11C, all the samples had a similar R infrared curve over the wave number from 516 to 5000 cm −1 by observing the same peak position and the similar increasing trend that R infrared values increased with decreasing wave number and tended to be stable after the 1000 cm −1 . The R infrared at 1000 cm −1 of different samples were different which proved that the w Ni affected the R infrared . By observing the R infrared at 1000 cm −1 over the w Ni ( Figure 11C and Table 6), it was found that no obvious decrease of R infrared happened until the w Ni reached 5.5 wt %, and the R infrared tended to be saturated when the w Ni reached 16.6 wt %. Therefore, the influence of the w Ni on the R infrared was considered to be classified into two stages: the stable stage (I: w Ni < 5.5 wt % and II: w Ni > 16.6 wt %) and the negative stage (5.5 wt % < w Ni < 16.6 wt %) ( Figure 11C). On the one hand, the initial R infrared was measured around 0.57 in the stable stage I and the lowest R infrared was measured around 0.473 in the stable stage II. On the other hand, the negative linear relationship (R 2 = 0.96) between the R infrared and w Ni was found in the negative stage. Similarly, the E m,infrared values at 1000 cm −1 was calculated according to the Equation (7) and schemed in Figure 11D. The E m,infrared values at 1000 cm −1 tended to be saturated to be around 0.527 when w Ni reached 16.6 wt %. Although the addition of Ni had a negative effect on the resistance of the Cu/Ni-coated Milife fabric against penetration of IR, the highest E m,infrared was around 0.527, which was still much smaller than the E m,infrared of the normal fabric (E m,infrared = 0.95 to 0.98). Therefore, the Cu/Ni-coated Milife fabrics had good resistance against penetration of IR.
Furthermore, the practical testing of the Cu/Ni-coated Milife fabrics for the thermal radiation resistance was carried out according to Section 2.3.4. The results are shown in Table 7. All the samples had the much lower T s (302-304 K) than the T h (313.15 K). In addition, a small decrease was observed by comparing the samples with Ni (N2-N8) with Cu-coated Milife fabric (N1), while there was no similar linear relationship between the T s and w Ni , which was different from the aforementioned standard IR resistance analysis. The phenomena may be caused by the higher porosity of the samples, where the infrared transmittance and the unexpectable heat convection existed during the measurement. The change of the air components in the measurement also accounted for the difference as well. Furthermore, by combining the results of the EMI and UV with the IR analysis, it was found that the addition of Ni only had a positive influence in the resistance against the penetration of electromagnetic waves when the wavelength only ranged from 290 to 400 nm in this case. Namely, the Ni had the selectivity on the resistance against the penetration of electromagnetic waves.

WCA on Ni-Coated Fabric
From the previous work, the WCA of the control sample (N0) was around 0 • , while the Cu/Ni coating supported the WCA [28]. Figure 12 described the outcomes of the w Ni on the wettability of the Cu/Ni-coated Milife fabrics. The Cu-coated Milife fabric (N2) had the WCA only of around 60.1 ± 1.0 • . Meanwhile, the WCA of the Cu/Ni-coated Milife fabric increased from 77.7 • to 114 • with increasing w Ni . N7 and N8 had the WCA higher than 110 • which confirmed the hydrophobicity of the surface. So, the erosion of the sample (N7 and N8) by the water could be relieved in reality [29].

WCA on Ni-Coated Fabric
From the previous work, the WCA of the control sample (N0) was around 0°, while the Cu/Ni coating supported the WCA [28]. Figure 12 described the outcomes of the wNi on the wettability of the Cu/Ni-coated Milife fabrics. The Cu-coated Milife fabric (N2) had the WCA only of around 60.1 ± 1.0°. Meanwhile, the WCA of the Cu/Ni-coated Milife fabric increased from 77.7° to 114° with increasing wNi. N7 and N8 had the WCA higher than 110° which confirmed the hydrophobicity of the surface. So, the erosion of the sample (N7 and N8) by the water could be relieved in reality [29].
In addition, the relationship between the WCA and wNi was roughly estimated by using exponential function (Equation (10)), where Cf was set roughly as 140° which was the highest value of the pure Ni surface coating among the various studies [30], Ci was the initial WCA of the Cu-coated Milife fabric without any Ni deposition (N1), and kc [°/wt %] was the estimated increasing rate of WCA with Ni deposition. The R 2 was 0.80 and kc was estimated as 0.032.

Conclusion
The present work successfully prepared the ultra-light Cu/Ni-coated Milife fabric (~10.57 g/m 2 ). The Cu/Ni deposition only covered the fibers and the interspace between the fibers was observed. The lowest air permeability of the Cu/Ni-coated Milife fabric was larger than 600 mm/s, which In addition, the relationship between the WCA and w Ni was roughly estimated by using exponential function (Equation (10)), where C f was set roughly as 140 • which was the highest value of the pure Ni surface coating among the various studies [30], C i was the initial WCA of the Cu-coated Milife fabric without any Ni deposition (N1), and k c [ • /wt %] was the estimated increasing rate of WCA with Ni deposition. The R 2 was 0.80 and k c was estimated as 0.032.

Conclusion
The present work successfully prepared the ultra-light Cu/Ni-coated Milife fabric (~10.57 g/m 2 ). The Cu/Ni deposition only covered the fibers and the interspace between the fibers was observed. The lowest air permeability of the Cu/Ni-coated Milife fabric was larger than 600 mm/s, which supported the good breathability. The addition of Ni in the Cu coating on the Milife fabrics did not affect the interaction between the metal particles (Ni and Cu) and the Milife fabrics (polyester fiber) by observing same peak positions in the A eff,infrared and T infrared curves in the Section 3.4. The WCA was improved by increasing w Ni and the Cu/Ni-coated Milife fabric became hydrophobic when the w Ni reached 15.2 wt %, which extended the usage of the Cu/Ni-coated Milife fabric.
The EMI, IR, and UV results proved that the Ni in the Cu coating on the Milife fabrics had the selectivity on the resistance against the penetration of the electromagnetic waves over the different wavelengths, which could be controlled by the w Ni : • Shielding EM wavelength. An obvious decrease in the EM SE of the coated Milife fabrics was observed when Ni was added. However, the EM SE of the samples were above 20 dB except for the sample N8 whose EM SE was around 19dB. A linear relationship between w Ni and EM SE was found (R 2 = 0.93). Besides, the ρ s of the Cu/Ni-coated Milife fabrics was smaller than 100 Ω/sq, which proved that the Cu/Ni-coated Milife fabrics had good conductivity. • IR wavelength resistance. The standard measurement of the IR reflectance proved that the decrease from 0.570 to 0.473 in the R infrared of the Cu/Ni-coated Milife fabrics was observed when the w Ni increased from 5.5 to 16.6 wt %. However, the surface temperature of the Cu/Ni-coated Milife fabric was measured almost in the same way by the custom-built setup and 11 K less than the heating source. It could be suggested that the good IR resistance effectiveness was obtained by depositing Cu/Ni particles on the Milife fabric and Ni did not affect the IR reflectance significantly. • UV wavelength resistance. It was interesting that the UPF was increased by adding the Ni in the Cu coating on the Milife fabric. The 40+ value was obtained when the w Ni reached 15.2 wt %.
As a result, the sample N6 (w Ni ) could be assumed as the optimized sample by considering the good shielding for EM, IR, and UV, but the Cu/Ni-coated Milife fabrics could also be selected for the specific usage. The prepared Cu/Ni could be used for the general applications like protection of the personal information from the near field communication, the protection of the pregnant woman from the electromagnetic radiation, incorporation with the outer wear for the protection from the UV and IR, and so on. Furthermore, it was interesting to observe that the effect of the increasing w Ni on the ray resistance against the electromagnetic waves became positive with the lower wavelength especially when the wavelength became smaller than 400 nm. Such trend may initiate the development of the novel materials for the selective ray resistance.