Impact of gamma irradiation on physico-chemical and electromagnetic interference shielding properties of Cu2O nanoparticles reinforced LDPE nanocomposite films

In the current work, cuprous oxide (Cu2O) nanoparticles coated with Tween 80 were successfully synthesized via the chemical reduction method. Nanocomposites composed of low-density polyethylene (LDPE) and different ratios of Cu2O nanoparticles were fabricated by the melt mixing process. 10% of ethyl vinyl acetate (EVA) as a compatibilizing agent was added to the molten LDPE matrix and the mixing process continued until homogenous nanocomposites were fabricated. To study the influence of ionizing radiation on the fabricated samples, the prepared species were exposed to 50 and 100 kGy of gamma rays. The synthesized Cu2O nanoparticles were investigated by transmission electron microscopy (TEM) and X-ray diffraction (XRD). XRD and TEM analysis illustrated the successful formation of spherical Cu2O nanoparticles with an average size of 16.8 nm. The as-prepared LDPE/Cu2O nanocomposites were characterized via different techniques such as mechanical, thermal, morphological, XRD, and FTIR. Electromagnetic interference shielding (EMI) of the different nanocomposite formulations was performed as a promising application for these materials in practical life. The electromagnetic shielding effectiveness (SE) of the produced samples was measured in the X-band of the radio frequency range from 8 to 12 GHz using the vector network analyzer (VNA) and a proper waveguide. All the samples were studied before and after gamma-ray irradiation under the same conditions of pressure and temperature. The shielding effectiveness increased significantly from 25 dB for unirradiated samples to 35 dB with samples irradiated with 100 kGy, which reflects 40% enhancement in the effectiveness of the shielding.

Since decades ago, the polymeric materials have concerned great interest in many applications owing to their excellent characteristics as flexibility, ease of processing and high mechanical strength.The development of the polymeric materials is of great importance and obtained by forming composites through the addition of inorganic fillers.Polymeric composite materials are widely used in diverse fields such as materials used in transportation, construction, electronics, and consumer products.Recently, polymer nanocomposites are a new class in which the additives have extremely small phase dimensions, usually on the order of a few nanometers.The production of polymer nanocomposites for diverse applications in place of conventional materials is increasing exponentially due to light weight, cost efficiency and their remarkable physicochemical characteristics such as mechanical strength, electrical conductivity, thermal stability and biological applications [1][2][3] .Polyolefin polymers such as

Experimental Materials
Copper sulfate pentahydrate was obtained from El-Goumhouria Co., Cairo, Egypt.Ascorbic acid was obtained from Merck Chemical Co., Germany.Tween 80 surfactant (T80) was obtained from MP Biomedical Co., India.Low density polyethylene pellets were obtained from El Sewedy Plastic Manufacturing (SEDPLAST), Tenth of Ramadan City, Cairo, Egypt.Ethylene vinyl acetate containing 18% of vinyl acetate was obtained from Arkema Inc., North America.Bidistalled water was utilized throughout the preparation steps.

Preparation of Cu 2 O nanoparticles
Cu 2 O nanoparticles were prepared by using aqueous solution reduction method with ascorbic acid as a reducing agent 34 .Firstly, CuSO 4 (0.015M) was dissolved in a T80 solution (0.5 wt% in water) under a magnetic stirrer at 65 °C for 30 min.After that, ascorbic acid (0.15M) was added into the CuSO 4 /T80 solution at 65 °C under continuous stirring, and then the solution pH value was raised and adjusted to pH 12 by using 2 M NaOH solution.After 30 min, the solution color changed to an orange colloid confirming the successful preparation of Cu 2 O nanoparticles.Cu 2 O nanoparticles were separated by centrifugation at 6,000 rpm and washed several times with water-ethanol solution, and then dried at room temperature for 24 h.

Fabrication of LDPE/Cu 2 O nanocomposites films
Nanocomposites films of LDPE containing Cu 2 O nanoparticles were prepared by melt blending process using a laboratory mixer (Plasticorder model PL-2100; Brabender, Germany)).Melt blending technique is a costeffective technique and widely used in the industry.Firstly, for melting of LDPE pellets, it injected in the hot mixer at temperature nearly 165 °C for 5 min 35 .After that, 10% of EVA as a compatibilizing agent was added into the molten LDPE with continued mixing for a further 5 min at the same temperature to achieve complete homogeneous mixing.Then, the nanocomposites were formed by mixing different concentrations (0, 1, 2, and 3 part per hundered resin (phr)) of Cu 2 O nanoparticles into the LDPE/EVA matrix at a rotor speed of 60 rpm for

Measurements
The X-ray diffraction (XRD) analysis the synthesized Cu 2 O nanoparticles and LDPE/Cu 2 O nanocomposites films was performed using an X-ray diffractometer (Shimadzu 6000, Tokyo, Japan) equipped with a Cu Kα (1.5418 Å) X-ray source.Both size and shape of the synthesized Cu 2 O nanoparticles was observed by Transmission electron microscopy (TEM) (a JEOL JSM-100 CX model instrument worked at 80 kV accelerating voltage).The infrared (IR) spectra LDPE/Cu 2 O nanocomposites films were measured using Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) apparatus (Bruker Vertex70, Germany) within the spectral range from 500 to 4000 cm −1 .The surface morphology of LDPE/Cu 2 O nanocomposites films was observed by scanning electron microscope (SEM) (ZEISS EVO-15, UK) operated at an acceleration voltage of 30 kV.For the SEM measurement, the fractured surfaces were coated with a thin layer of gold in order to avoid electrical charging under the electron beam.For obtaining the mechanical analysis of LDPE/Cu 2 O nanocomposites films, a dumbbell-shaped examination sections were measured at 300 mm/min of crosshead speed via a tensile testing machine (Qchida computerized testing instrument; Dongguan Haida Equipment Co. Ltd; China).The ISO 527-2 was detected.The average value of the mechanical factors was taken via at least three testers.Thermogravimetric (TG) analysis was performed using a Shimadzu TGA-50 (Kyoto, Japan) to study the thermal stability of nanocomposites.The temperature monitored from ambient to 600 °C at a heating rate of 10 °C/min with a nitrogen flow of 20 mL/ min.Direct current (DC) conductivity measurements for LDPE/Cu 2 O nanocomposites films were carried out at room temperature.The sample was positioned in a conductivity measuring cell in a sandwich configuration.HP 4280A C-V Plotter (USA) was used for measuring the conductivity of the samples under test.

Electromagnetic interference assays
Shielding effectiveness for the unirradiated and irradiated nanocomposites with gamma doses of 50 and 100 KGy was measured using a vector network analyzer and a proper wave guide.This measurement uses the R&S ZVA 67 VECTOR NETWORK ANALYZER operates in the range 10 MHz to 67 GHz and a wave guide operates in the X-band from 8 to 12 GHz.The VNA manufactured in Germany by Rohde & Schwarz GmbH & Co KG.The measuring setup was shown schematically in Fig. 2.

Characterization of Cu 2 O nanoparticles X-ray diffraction analysis of Cu 2 O nanoparticles
The XRD analysis is an indispensable step in gaining information about the crystal structure and phase analyses of nanomaterials. Figure 3  where k, λ, β and θ are the shape or geometry factor (k = 0.9), X-ray wavelength (λ = 0.1541 nm), the full width at half maximum (FWHM) of diffraction peak and the diffraction angle, respectively.Using the FWHM of the strong and sharp diffraction peak (111), the crystallite size was found to be approximately 13.08 nm.

Mechanical measurements
The stress-strain curve is displayed in Fig. 5A,B.As clear, the stress of LDPE increased with Cu 2 O nanoparticles, at the same time the nanocomposite reinforced with 2 phr of Cu 2 O clear superiority about the other for each un-irradiated and irradiated sample.Whereas, the strain of the nanocomposites was reduced with nanoparticle interface due to the rigidity and stiffness brought into LDPE texture.Furthermore, the irradiation dose declined the strain due to the restricted mobility caused by radiation-induced crosslinking effect.The explanation of the previous stress-strain curve through the studying of the tensile strength (TS), and elongation at break (E%) were implemented for the fabricated sheet samples of the LDPE and LDPE/Cu 2 O nanocomposite specimens, respectively, as specified in Fig. 6.A low content of a dispersed additive (up to 2.0 phr) could develop the tensile properties of LDPE (Fig. 6A).This phenomenon is credited to the uniform distribution of additive nanoparticles 37,38 .Controlling the concentration of distributed fillers is established on the reduction in strength property of materials at concentrations above the stated upper threshold values.If the concentration of additive or filler surpasses the threshold values, an accumulation of particles happens in the polymeric matrix, leading to a decline in strength features.This observation was achieved when the percentage of the Cu 2 O nanoparticles was 3.0 phr 38 .On the other hand, as the radiation dose increases from 50 to 100 kGy more crosslinking is created in the polymeric chains leading to increase in TS values and also the synergistic effect of both irradiation doses and filler contents up to 2.0 phr lead to the enhancement of the tensile strength values.Consequently, the two applied irradiation doses and interface of nanoparticle up to 2.0 phr improved the TS of polymer matrix due to the synergism effect between them.From Fig. 6B, Inverse effects were predominant in case elongation at break studies caused by nanofiller and radiation doses.The reduction in elongation at break with rising filler contents can be ascribed to the restriction in mobility of polymer chains that occurred by adhesion and interaction of nanofiller that did not allow the polymer chains to move causing a decrease in elongation 39 .On the other hand, the decrease in elongation at break with rising radiation doses is credited to the radiation-induced crosslinking effect 40 .The crosslinking cause the binding of adjacent polymeric chains and consequently the molecular mobility is hindered and a rupture for polymeric chains takes place at lower elongation value 41 .

FTIR investigation
In the spectral range of 4000-500 cm −1 , bands of the FTIR were stately by plotting a graph of wave number (cm -1 ) against transmittance (%). Figure 7A was listed to recognize the probable interface between the LDPE/ EVA matrix and Cu 2 O nanoparticles at various percentage loading.From Fig. 7A several bands are distinct to the successful blending of LDPE and EVA such as, CH 2 stretching at 2920 cm −1 and its bending vibration at 615 cm −1 which corresponds to LDPE and EVA.Furthermore, the band at 1745 cm −1 , matches the C = O stretching of the EVA acetate group.After interfacing of Cu 2 O nanoparticles into the LDPE matrix, the FTIR of the strengthened nanocomposites doesn't show evident alterations in the FTIR spectra of the LDPE matrix reflecting the physical interaction of Cu 2 O nanoparticles inside LDPE matrix 42 .Figure 7B represents the FTIR of irradiated LDPE and The peak intensity of carbonyl group at 1745 cm -1 slightly increased after irradiation due to the occurrence of oxidative phenomena during irradiation and formation of the carbonyl group 43 .After irradiation, OH broad band appear at 3400 cm -1 in LDPE and its nanocomposite are due to the presence of oxygen surrounding in gamma irradiation cell and occurrence of some chain scission 44 .diffraction peak intensity of LDPE was reduced due to the decrease in the crystallinity.This result supported the good interfacial interaction between the Cu 2 O nanoparticles and the polymer chains with the formation of homogeneous nanocomposite 39 .No diffraction peaks corresponding to Cu 2 O nanoparticles are observed in the LDPE nanocomposites due to their low concentrations 42 .Moreover, the shifting occurs for the peak at 36° of LDPE is due the interference with main peak of Cu 2 O nanoparticles.On the other hand, irradiated LDPE/Cu 2 O nanocomposite at 100 kGy displayed in (Fig. 9) showed an enhancement in crystallinity.This consequence is qualified to crosslinking effect of gamma radiation 45,46 .

Thermogravimetric analysis (TGA)
The TGA investigation is a characteristic procedure in which alterations in the mass are detected as the sample is progressively heated.The thermal stability of LDPE reinforced with different ratios of Cu 2 O nanoparticle is measured and displayed in Fig. 10 and the several degradation stages are itemized in Table 1.By following the TGA curves exhibited in Fig. 10    We selected LDPE/ Cu 2 O (2 phr) nanocomposite as the best component that had achieved good mechanical properties to study the effect of irradiation dose on its thermal stability (Fig. 11).Obviously, the thermal stability of native irradiated LDPE was decreased at the early stages of decomposition (Tm 10 and Tml 25 ) due to the release of volatile compounds and water vapor.On the other hand, at lately stages of the decompositions (Tm 50 and Tm 75 ), it shifted to a higher value when exposed to gamma irradiation.This is credited to the effect of gamma irradiation and crosslinking density creation inside the LDPE matrix.Furthermore, for irradiated LDPE and LDPE/ Cu 2 O (2 phr) nanocomposite, the superior thermal stability of nanocomposite reflect the synergistic impact of both nanoparticle and gamma irradiation on the thermal stability of the pristine LDPE.and found that the direct energy gap decreases with increasing radiation doses and their results ascribed to the radiation effect that increases the number of free electrons which enhance the electric conductivity significantly 47 .Also, Elnaggar et al. (2023) 38 , Abdel Maksoud et al. (2021) 48 , Tommalieh (2021) 49 and found that gamma radiation decreases the energy band gap of polymer/metal oxide nanocomposites due to the increase the number of energylocalized electronic states between the valence and conduction bands related to the subjection to gamma radiation where the chains becoming more and more cross-linked with one another as a result of subsequent irradiation .

Electromagnetic shielding effectiveness
The ability of a material to attenuate the propagation of an incident electromagnetic wave defines the concept of electromagnetic shielding perfectly.The attenuation of these waves may be due to reflection absorption and even    The shielding effectiveness of the LDPE/Cu 2 O nanocomposite samples after 50 kGy of gamma-ray irradiation is presented in Fig. 15A.The response is similar to that of the unirradiated samples but the shielding effectiveness improved significantly.On the other hand, with increasing gamma radiation to 100 kGy (Fig. 15B), the response is similar to both the unirradiated and irradiated with 50 kGy samples but the shielding effectiveness improved significantly.The enhancing EMI shielding process is attributed to the enhancement of the conductivity by gamma radiation and Cu 2 O nanoparticles on LDPE polymeric matrix [51][52][53] .
A study of the radiation effect on each sample is presented in Fig. 16.Each graph in this figure represents the response of each sample before and after irradiation.It is clear that the increase in the radiation dose enhances the shielding effectiveness of the prepared samples.The shielding effectiveness improved significantly from 25 dB for unirradiated samples to 35 dB when irradiated with 100 kGy, which reflects 40% enhancement in the effectiveness of the shielding.

Conclusions
This article presented the synthesis and investigation of gamma irradiated LDPE/Cu 2 O nanocomposites.TEM and XRD investigations proved that the Cu 2 O nanoparticles were successfully formed with particle size equal 16.8 nm.Based on the mechanical results, we conclude that the Cu 2 O nanoparticles positively tensile test results on LDPE matrix at 2 phr Cu 2 O nanoparticles and 100 kGy.SEM results show a homogeneous dispersion of nanofillers inside LDPE matrix.From TGA analysis, the thermal stability of LDPE/Cu 2 O nanocomposites clearly improved with all Cu 2 O percentages.The shielding effectiveness was measured for unirradiated and irradiated nanocomposites with gamma radiation doses (50 and 100 kGy).The results of SE increase significantly with the increase of both the concentration of Cu 2 O nanoparticles and the radiation doses.In conclusion, the findings of our investigation witness the remarkable scope and potency of LDPE/Cu 2 O nanocomposites as efficient product for electromagnetic interference (EMI) shielding and radiation pollution which lead to the detrimental effects on sensitive precision electronics and on human health.
represents the XRD peaks of Cu 2 O nanoparticles.The XRD spectrum of the Cu 2 O nanoparticles showed the distinctive diffraction peaks observed in the spectra at 30.01, 36.88,42.72•, 61.88•, and 73.96• correspond to the crystal planes (110), (111), (200), (220) and (311), respectively, of the cubic phase of cuprous oxide (Cu 2 O) 36 .Also, the sharp diffraction peaks of Cu 2 O nanoparticles indicating that these Cu 2 O nanoparticles have high crystallinity.The crystallite size of Cu 2 O nanoparticles (D) was considered based on the main plane of (111) using Scherrer formula (D = kλ/βcosθ),

Figure 2 .
Figure 2. The measuring setup using the vector network analyzer.

Figure 4 .
Figure 4. TEM image with different magnifications and the particle size distribution by Gaussian fitting of Cu 2 O nanoparticles.

Figure 8 .
Figure 8. XRD patterns of LDPE and LDPE/Cu 2 O nanocomposite with different concentrations.

Figure 13 .
Figure 13.DC conductivity of LDPE films with different concentrations of Cu 2 O nanoparticles at various gamma irradiation doses.

Figure 14 .Figure 15 .
Figure 14.Represents the Shielding Effectiveness in (dB) versus frequency in (GHz) for the unirradiated samples.
and the mass loss values recorded in Table1, the values show that the decomposition stages of the nanocomposite mass loss mainly depend on the Cu 2O filling and applied radiation dose.It is apparent that the LDPE/Cu 2 O nanocomposite's thermal stability clearly improved with all Cu 2 O percentages.To examine the magnitude of LDPE thermal stability affected by Cu 2 O nanoparticles, wherein the different temperature mass loss, Tml 10 , Tm 25 , Tm 50 , and Tm 75 and residual weight at 600 °C of the native LDPE recorded respectively, 365 °C, 382 °C, 409 °C, 452 °C, and 0.6%.These values shifted to higher temperature mass loss by incorporating 2 phr of Cu 2 O as an example, reflecting the thermal stability of the polymer matrix which was arranged respectively as follows, 426 °C, 437 °C, 441 °C, 444 °C, and residual weight at 1.2%.
Figure 13 indicates the conductivity characteristics of LDPE films with different concentrations of Cu 2 O nanoparticles and gamma irradiations.It can be seen that the conductivity of LDPE increases with the incorporation of Cu 2 O nanoparticles.Also, the conductivity enhanced significantly with increasing gammairradiation doses from 50 to 100 kGy.Abdel Moez et al. studied the impact of gamma radiation on LDPE films LDPE/