Preparation and properties of novel binary and ternary highly amorphous poly(vinyl alcohol)-based composites with hybrid nanofillers

1 Vol.:(0123456789) Scientific Reports | (2023) 13:19126 | https://doi.org/10.1038/s41598-023-46083-2 www.nature.com/scientificreports Preparation and properties of novel binary and ternary highly amorphous poly(vinyl alcohol)‑based composites with hybrid nanofillers Anastasiia Stepura 1*, Matej Mičušik 1, Federico Olivieri 2, Gennaro Gentile 2, Marino Lavorgna 2,3, Maurizio Avella 2, Edita Matysová 4, Jarmila Vilčáková 5 & Mária Omastová 1* Smart protective coatings and devices are currently of great interest. In particular, they can absorb or reflect harmful waves of electromagnetic interference (EMI). In this work, novel binary and ternary composites with highly amorphous poly(vinyl alcohol) (HAVOH) as a matrix and single‑walled carbon nanotubes (SWCNTs) and MXenes as nanofillers were prepared. HAVOH is a recently patented kind of poly(vinyl alcohol) (PVOH) that was modified with diol monomers. MXenes are a new type of inorganic two‑dimensional (2D) nanoparticle consisting of carbides, nitrides and carbonitrides. Three series of composites, HAVOH/SWCNTs, HAVOH/MXenes and HAVOH/SWCNTs/MXenes, were prepared using the solvent casting method. Samples were tested with various methods to study their structure, electrical properties, thermal behavior and EMI‑shielding properties. HAVOH/3.0 wt.% SWCNTs/3.0 wt.% MXene specimens revealed a shielding effectiveness of 55 dB, which is 122 times better than that of the neat matrix. These results are promising for the fabrication of films with protective effects against EMI. Demand for innovative polymeric composites is continually growing. The preparation of this class of materials, especially low-cost and high-performance polymeric composites, is still a challenge for researchers. An important factor is also the selection of the polymeric matrix. Most polymers require the utilization of some organic solvents for their dissolution, and large-scale production is often not environmentally acceptable. Thus, polymeric composites prepared with solvent casting using water-soluble materials have better opportunities for application. There are few water-soluble polymers produced on a large scale. Among them, one of the most relevant is poly(vinyl alcohol) (PVOH). Among different PVOH types, recently, a modified PVOH containing diol monomers named highly amorphous poly(vinyl alcohol) (HAVOH), trademark G-Polymer, was produced1. The main advantages of HAVOH over typical PVOH are its semicrystalline nature, excellent water solubility, good melt processing by extrusion and low oxygen permeability but poor water barrier resistance, which makes it hard to use in food packaging, requiring the utilization of additives as well as crosslinkers2–4. On the other hand, HAVOH can be used for polymeric nanocomposite preparation. As shown by Donato etal.3, HAVOH represents an effective matrix for the realization of multifunctional nanocomposites with good electrical, mechanical and thermal properties. Besides that, HAVOH was applied as a matrix for the preparation of composites with different fillers, such as multiwalled carbon nanotubes (MWCNTs)5, graphite6, graphene oxide7, clay2, silica3, cellulose8, and single-walled carbon nanotubes (SWCNTs)9,10. In some cases, it is difficult to find a solvent that is suitable for both HAVOH dissolution and filler dispersion, and specific methods are required to process the nanocomposite formulation. Santillo etal.5, who used MWCNTs as fillers, previously dispersed nanotubes in OPEN 1Polymer Institute of Slovak Academy of Sciences, Dúbravská cesta 9, 845 41 Bratislava, Slovakia. 2Institute of Polymers Composites and Biomaterials, National Research Council of Italy, Via Campi Flegrei 34, 80078 Pozzuoli (Naples), Italy. 3Institute of Polymers Composites and Biomaterials, National Research Council of Italy, Piazzale Enrico Fermi 1, 80055 Portici (Naples), Italy. 4SYNPO akciová společnost, S. K. Neumanna 1316, 532 07 Pardubice V, Czech Republic. 5Faculty of Technology, Tomas Bata University in Zlín, Vavrečkova 5669, 760 01 Zlín, Czech Republic. *email: [email protected]; [email protected] 2 Vol:.(1234567890) Scientific Reports | (2023) 13:19126 | https://doi.org/10.1038/s41598-023-46083-2 www.nature.com/scientificreports/ THF (tetrahydrofuran) with the addition of an ionic liquid, enabling them to interact with the selected filler. When HAVOH was added, a stable dispersion of polymer coated with filler was formed, as HAVOH was not soluble in the aforementioned solvent, but it formed hydrogen bonds with the applied ionic liquid (BenzImCl— 1-Benzyl-3-methyl-imidazolium chloride). The prepared samples showed good electrical conductivity, 0.79S/ cm and were processed by 3D printing, obtaining effective EMI-shielding systems. In the last decade rising number of different kinds of devices, expanding of areas (territories) of cover with wireless local area networks and radars, significantly increased the level of so-called "electric field pollution". It creates electromagnetic radiation due to radio waves and microwave radiation, which is emitted by all electronic devices, particularly those that operate in the radio wave and microwave range of frequencies (e.g., cell phones). Consequently, such phenomenon causes electrosmog. Of great concern is that the radiation interferes with electronics, due to the interaction of the electrons in the metal conductors with the electric field in the radiation11. Hence, it causes malfunctions of aforementioned devices and it can also cause human health problems. Therefore, currently researchers are highly engaged in creating a new class of materials called electromagnetic interference (EMI) shielding materials12. For good shielding effectiveness (SE) materials have to possess high electrical conductivity (EC). Pure metals such as copper, aluminum, stainless steel have an outstanding conductivity, thus prominent SE. However, they are expensive, with low flexibility, high density, and tend to easily corrode. Recently, nanoparticles become of great interest in the view of application in EMI-shielding area. This is due to higher aspect ratio, higher interfacial reactivity, and unique chemical and physical properties due to nanoscale sizes. Among others, 2D MXenes are recently discovered very promising family of inorganic nanoparticles. MXenes were first obtained and described in 2011 at Drexel University, USA13,14. The first article devoted to MXene discovery reported the preparation of Ti3C2Tx from the Ti3AlC2 MAX phase precursor13. MXenes consist of quite thin (only a few atoms) layers of transitional metal carbides, nitrides, and/or carbonitrides. The general formula of MXenes is Mn+1XnTx, where M is an early transitional metal (Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, or W), X is carbon and/or nitrogen, and n = 1–3. T represents the surface termination groups that are mostly = O, -F, -OH, and x in Tx represents the number of surface functionalities. MXenes have an impressive list of properties, such as a high Young’s modulus15, good thermal and electrical conductivities16,17, adjustable band gap18, UV-light absorbance19, good EMI-shielding properties20, and large energy capacitance21. Due to possessing a variety of properties, MXenes are promising candidates for numerous applications, and among others, these nanoparticles could be used as fillers in polymeric nanocomposites22. Currently, more than 40 different MXenes have been prepared and described, and over 100 stable compounds have been theoretically predicted23,24. MXenes possess few properties, which are favorable for their application as EMI-shielding barriers. First of all, their layered structure, as due to this, incident waves when entering the structure "interact with the high electron density of MXene, leading to an ohmic loss of EM waves"25, and later they are changed into multiple intrinsically reflected (absorbed) waves, thus significantly decreasing the number of transmitted waves. Secondly, MXenes high EC also plays an important role. It is advantageous in this application field as this means high number of free electrons and high-density electronic cloud. The presence of free electrons provides reflection of the incident electromagnetic waves. Additional properties, which make MXenes promising EMI-shielding material, are large specific surface area, which can be adjusted through synthesis conditions, lower density, comparing to heavy metals, ultralow thickness. Ti3C2Tx MXene was first investigated for its absorption performance in 2016, comparing it to that of the corresponding MAX phase (Ti3AlC2). The results showed that when a material thickness of 1.4mm was used at a filling ratio of 50 wt.%, the extreme reflection loss of Ti3C2Tx was −17dB, which was much lower than that for the MAX phase26. The EMI shielding parameters of MXenes can be enhanced when combined with polymers, various types of fibers, carbon derivatives, metals, metal–organic frameworks and other materials, as described in published papers27–29. In the work of Shazad etal.30 MXenes were firstly studied in a composite for their EMI SE (shielding effectiveness) properties. They prepared Ti3C2Tx—sodium alginate samples and received 57dB of SE. Another excellent result was obtained by Liu etal.31, who fabricated flexible, hydrophobic MXene foams, which revealed outstanding 70dB of EMI-shielding performance. Even better values were achieved by Nguyen etal.32. In this work authors prepared hybrid composites with introducing both MXenes nanoparticles and graphene foam (GF) into PDMS (poly(dimethylsiloxane)) polymer matrix. The highest average EMI SE was achieved with Fe3O4@Ti3C2Tx/GF/PDMS sample reaching 80dB in X-band, 77dB in Ka-band, 83.6dB at 8.7GHz and 78.9dB at 39.6GHz. This specimen containing 11.5% of Fe3O4@ Ti3C2Tx with thickness 1mm showed also superb 630 S/cm of conductivity. Slightly lower results were obtained in the work of Song etal.33. Here were prepared also hybrid composite, however instead of graphene was used honeycomb structural reduced graphene oxide (rGH) and as a matrix was used epoxy resin. Addition of only 1.2 wt.% of rGH and 3.3 wt.% of MXenes led to receiving ~ 390 S/cm of electrical conductivity and 55dB of shielding effectiveness. In the next work fabricated composites are close to those mentioned in this work in the viewpoint of polymer matrix. Jin etal.34 prepared flame-retardant multilayered films with MXene filler and PVA (poly(vinyl alcohol)). The 27-μm thick PVA/MXene film exhibited remarkable 716 S/cm of EC and ~ 44dB of EMI SE. However, as much as 19.5 wt.% of filler load was used in this specimen. At the same time, composite revealed 23-fold enhanced thermal conductivity, comparing to neat PVA, what is a promising result for further application as films for prevention of flame propagation. In this work, a new type of HAVOH-based polymeric nanocomposite was prepared by solution casting, mixing an aqueous solution of HAVOH with various amounts of delaminated 2D MXene in a water suspension. Moreover, nanocomposites containing a 1D filler, SWCNTs, were prepared by the same method. The combination of 1D and 2D fillers is an interesting approach for innovative polymeric composite creation with high application potential; therefore, a third series of HAVOH composites was prepared containing a hybrid mixture of MXenes and SWCNTs. Prepared nanocomposites were characterized using a multitechnique approach. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the morphology and structure of the obtained nanocomposites, broadband dielectric spectroscopy (BDS) was used 3 Vol.:(0123456789) Scientific Reports | (2023) 13:19126 | https://doi.org/10.1038/s41598-023-46083-2 www.nature.com/scientificreports/ for electrical conductivity measurements. The application potential was examined by EMI-shielding analysis to obtain knowledge about the composite electromagnetic behavior. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were performed to study the thermal decomposition behavior. The novelty of this work is in the preparation of binary HAVOH/MXenes and ternary HAVOH/SWCNTs/ MXenes composites, their complex study, which revealed remarkable EMI-shielding performance of hybrid composites, what is a promising basis for applications in this field. Methods Multilayered, nondelaminated MXenes Ti3C2Tx were received as a water-based paste from Drexel University (Philadelphia, Pennsylvania, U.S.A.) with a concentration of 0.767g of MXenes per 1g of MXene paste. Highly amorphous poly(vinyl alcohol) (HAVOH) powder (commercialized under the trade name G-polymer, grade OKS-1089, Nippon Gohsei, Japan) was provided by Mitsubishi Chemicals. Single-walled carbon nanotubes (SWCNTs) (purity 80–93%) were purchased from Tuball™ (OCSiAl Europe S.a.r.l., Grand Duchy of Luxembourg). To obtain a delaminated single-layered MXene solution, MXene paste was mixed with LiCl (1g of Ti3C2Tx:1g of LiCl) in 20ml of deionized (DI) water. The beaker with the mixture was placed into a water bath and placed on a magnetic stirrer. It was left at 35°C and 150rpm for stirring overnight. The next day, it was centrifuged at 3500rpm until the supernatant became black. In further steps, the centrifugation cycle time was increased to 1h. When the supernatant turned dark green, it contained delaminated single-layered MXene sheets, so it was the start of solution collection. When the solution started to appear light-green or transparent, centrifugation was stopped. To obtain the concentration of the prepared solution, using 20mL of the solution and Celgard®3501 membrane, this portion of the solution was filtered with vacuum-assisted filtration (VAF), obtaining almost dried MXene powder as a film (Fig.1). To remove residual water, the membrane with MXene film was put into a vacuum oven for drying at 45°C until the next day. As a next step, the concentration of MXenes in the prepared single-layer solution was calculated. Concentrations were usually in the range of 0.1–0.5mg/ml; therefore, the reconcentration process with a rotary vacuum evaporator was performed to increase the concentration. All composites were prepared with solvent casting using water as a solvent. Table1 summarizes the presented compositions and short names of the fabricated HAVOH-based polymeric nanocomposites, and Fig.2 schematically shows the preparation processes. To prepare HAVOH/SWCNTs composite samples first, HAVOH powder was added to deionized (DI) water. Solutions containing 3.0 wt.% of polymer were prepared using a magnetic stirrer for 30min at 50°C, then the Figure1. Free-standing film of MXenes prepared by VAF on a Celgard membrane (Ø = 4cm, h = 18μm). Table 1. Composition of HAVOH-based specimens. HAVOH (H), wt.% SWCNTs, wt.% MXenes (MX), wt.% Short name 100 – – H 99.0 1.0 – H/1 SWCNTs 97.0 3.0 – H/3 SWCNTs 98.6 – 1.0 H/1 MX 97.0 – 3.0 H/3 MX 96.0 3.0 1.0 H/3 SWCNTs/1 MX 95.0 3.0 2.0 H/3 SWCNTs/2 MX 94.0 3.0 3.0 H/3 SWCNTs/3 MX 4 Vol:.(1234567890) Scientific Reports | (2023) 13:19126 | https://doi.org/10.1038/s41598-023-46083-2 www.nature.com/scientificreports/ temperature was increased to 90°C and left for further stirring for 30min. Depending on the concentration of the filler in the sample, a calculated amount of SWCNTs was added to DI water and sonicated with an ultrasonic probe for 1h (100% amplitude, cycle—1). Then, the mixture was added to HAVOH and left for mixing under continuous stirring for 30min. In the next step, the HAVOH/SWCNTs mixture was mixed at 1200rpm for an additional 3h using a mechanical stirrer. Afterward, the mixture was poured out into a polytetrafluoroethylene (PTFE) Petri dish and dried at 60°C under vacuum for total water evaporation, which took 5days. This film was cut into small pieces for further processing with compression molding. For preparation of HAVOH/MXenes composite samples the HAVOH dispersion preparation procedure was the same as described above. According to the desired filler load, a calculated amount of MXene solution was added to dissolved HAVOH and left for mixing for 30min. In the next step, the beaker containing the HAVOH/ MXene mixture was mechanically stirred at 1200rpm for 3h. Then, the mixture was poured out into a PTFE Petri dish dried at 60°C under vacuum for 5days for total water evaporation, and the obtained film was cut for compression molding. To obtain HAVOH/SWCNTs/MXenes hybrid composites, the preparation procedures described above were combined. First, HAVOH was dissolved in water, and then SWCNTs and MXene suspensions were added and mixed on a magnetic stirrer. Afterward, the mixture was mechanically stirred at 1200rpm for 3h, poured into PTFE Petri dishes and processed as described above. Circles of 0.3mm thickness and 2.5cm in diameter were prepared by compression molding of the prepared composites using a laboratory hydraulic press SRA 100 (Fontijne, Netherlands) at 2.4MPa and at 220°C for 10min. X-ray photoelectron spectroscopy (XPS) signals were recorded using a Thermo Scientific NEXSA G2 Surface Analysis System (Thermo Fisher Scientific, UK) equipped with a microfocused, monochromatic Al Kα X-ray source (1486.68eV). An X-ray beam of 400µm size was used. Spectra were acquired in the constant analyzer energy mode with a pass energy of 200eV for the survey. Narrow regions were collected using a pass energy of 50eV. Charge compensation was achieved with the system dual beam flood gun. Thermo Scientific Avantage software, version 6.6.0 (Thermo Fisher Scientific, UK), was used for digital acquisition and data processing. Spectral calibration was determined by using the automated calibration routine and the internal Au, Ag and Cu standards supplied with the K-Alpha system. Surface compositions (in atomic %) were determined by considering the integrated peak areas of the detected atoms and the respective sensitivity factors. The morphology of the investigated samples was observed by a JEOL 7600F Schottky field emission scanning electron microscope (SEM FES) (Jeol Ltd., Tokyo, Japan). The nanocomposites with HAVOH as the matrix were investigated at an accelerating voltage of 5kV in high vacuum. Before SEM analysis, samples were sputtered with a thin layer of gold by a Balzers SCD 040coater (Balzers Union Limited, Balzers, Liechtenstein). AzTec software (Springfield, NJ, USA) was used to collect figures. For SEM, all samples were fractured in liquid nitrogen, and afterward, these cross-sectional areas were scanned. Bright-field transmission electron microscopy (TEM) analysis was carried out by means of a FEI Tecnai G12 Spirit Twin (LaB6 source) equipped with a FEI Eagle 4k CCD camera. The accelerating voltage was set at 120kV. Before analysis, ultrathin sections of nanocomposite samples (nominal thickness 150nm) were obtained at room temperature under dry conditions by using a Leica UC6 ultramicrotome and deposited on 400 mesh copper grids. Broadband dielectric spectroscopy (BDS) measurements were performed by a Novocontrol Concept 40 with an Alpha dielectric spectrometer provided by Novocontrol Technologies GmbH (Germany) in the frequency Figure2. Scheme of preparation of three series of HAVOH polymeric nanocomposites. 5 Vol.:(0123456789) Scientific Reports | (2023) 13:19126 | https://doi.org/10.1038/s41598-023-46083-2 www.nature.com/scientificreports/ range of 10–1Hz to 106Hz. A BDS 1200 (supplied by Novocontrol Technologies) parallel-plate capacitor with two gold-plated electrodes was used as a test cell. AC parameters were measured after vacuum depositing gold electrodes (20mm in diameter) on both sides of pelletized samples to ensure electrical contact. Frequency scans were conducted for each of the examined specimens. The diameter of the specimens was 40mm. Thickness ranges were between 0.2 and 0.5mm depending on the specimen. The system is fully automated, and WinDeta software was used for system control and data acquisition. The EMI shielding effectiveness of the prepared nanocomposite sheets (length × width = 2.3 × 1cm, thickness—1mm) was studied with a vector network analyzer (Agilent N5230A) at 8.2–12.4GHz frequency range (the so-called X-band) using a waveguide sample holder. The electromagnetic interference shielding refers to the attenuation of the transmitting electromagnetic waves by the shielding material. A high value of electromagnetic interference (EMI) shielding effectiveness (SE) means less energy transmitted through the shielding material. For commercial applications, a shielding material which possesses the (SE) of 20dB can block 99% of the incident electromagnetic waves. The electromagnetic shielding effectiveness (SE) can be expressed as the ration of transmitted power corresponding to the incident power of the EM wave, as: where, PT (ET or HT) and PI (EI or HI) symbolized transmitted power and initial power (electric and magnetic field intensity) of EM wave respectively. Here, SER and SEA are the shielding effectiveness because of reflection and absorption, respectively. SEM is the shielding effectiveness due to multiple reflections inside the material, which can be negligible when SET > 10dB. The total shielding efficiency (SET) is given as Eq.(2): The shielding effectiveness of the (magnetic/conductive) polymer composite filled e.g. with graphene oxide can be evaluated on the basis of scattering parameters (S11, S12, S21, S22) by following Eqs.(3), (4): A two-port network analyser can be utilized to measure the scattering parameters (S11, S12, S21 and S22), which correlates with reflection (R) and transmission coefficients (T): The relationship between reflected (R), absorbed (A), and transmitted (T) portions of electromagnetic wave intensity follows: Using this equation, direct determination of R and T from measured values of S11 and S21, respectively, enables one to extract absorbed part (A) of electromagnetic wave intensity11. Thermal characterization was performed using a differential scanning calorimeter (DSC-Q1000, TA, USA) in a flowing nitrogen atmosphere with a gas flow rate of 50mL/min. Samples were preliminarily heated from 0 to 220°C with a heating rate of 10°C/min to erase their thermal history. Then, after an isotherm at 220°C for 5min, a cooling scan until 0°C at 10°C/min and a second heating scan from 0 to 220°C at a rate of 10°C/min were performed. Thermal parameters (glass transition temperature Tg, melting temperature Tm, and melting enthalpy ΔHm) on the second heating scan were calculated. Thermogravimetric analysis (TGA) measurements were carried out on a TGA Q500 thermogravimetric analyzer (TA Instruments, USA). For the actual analysis, a small amount of sample (on the order of tens of mg) was prepared and transferred into a platinum pan. Measurements were carried out at a heating rate of 10°C/ min from laboratory temperature to 900°C in an air atmosphere. Consent to participate All authors contributed to the research presented in the paper and approved their participation. Results and discussion Highly amorphous poly(vinyl alcohol) is a biodegradable polymer based on poly(vinyl alcohol) modified with diol monomers (Fig.3), which is also water soluble. There are only a few water-soluble polymers. This property was favorable for our work on the fabrication of HAVOH-based composites with MXenes because MXenes were received as a water-based paste, and their further processing, e.g., delamination, was also performed in water. In this study, we worked with nonoxidized MXene paste, which is described in detail here (labelled “MX2” in (1) SE (dB)=SER+SEA+SEM=10log  PT PI =20log  ET EI =20log  HT HI, (2) SET(dB)=SER+SEA. (3) SE R=10log10 1 1−R =10log10 1 1−|S11| 2  (4) SE A=10log10  1−R T =10log10  1−|S11| 2 |S21| 2 . (5) T=|S12|2=|S21|2 (6) R=|S11|2=|S22|2. (7) R2+A2+T2=1 6 Vol:.(1234567890) Scientific Reports | (2023) 13:19126 | https://doi.org/10.1038/s41598-023-46083-2 www.nature.com/scientificreports/ Ref.35). Delaminated MXene showed no oxidation (only 2.9 at.% of Ti4+ signal ca. 458.5eV) and was very clean with a low amount of sp3 carbon of 6.1 at.% (Fig.S1, TableS1). Only a small amount of aluminum remained from the MAX phase in the structure (TableS1). The hydrophilic character of this type of MXene was discussed and proven in Ref.36. Thus, it was not necessary to transfer these 2D fillers from water to another solvent, which could cause additional difficulties, such as lower yield due to losses during the transfer process, agglomeration and sedimentation. As a 1D nanofiller, single-walled carbon nanotubes (SWCNTs) were used. The main reason is that SWCNTs have higher electrical conductivity than MWCNTs37,38. SWCNTs are hydrophobic, which is also evident from the surface composition determined by XPS, where approximately 80.9 at.% sp2 carbon is on the surface and only approximately 1.7 at.% oxygen provides hydrophilic character (see Fig.S2 and TableS2). Therefore, it was challenging to prepare homogeneous composites. We prepared and characterized binary and ternary composites with the HAVOH matrix and 1D SWCNTs and 2D MXenes as fillers (Table1). Study of the morphology and intrinsic structure are very important characteristics for further interpretation of the material properties. The orientation of the fillers, their dispersion, presence of agglomerates, incorporation into the polymer matrix, interaction between the matrix and the filler with other fillers or additional helping components, e.g., copolymers, surfactants, compatibilizers, etc., affect the properties of the final material. Poor dispersion of fillers, the presence of agglomerates, and incompletely evaporated solvent residues can worsen the electrical and mechanical properties of polymeric nanocomposites. Study of the morphology and structure of HAVOH-based composite samples was performed with SEM and TEM. In Fig.4, SEM micrographs of the pure HAVOH matrix (Fig.4a), binary composites HAVOH/1.0 wt.% MXenes (Fig.4b), HAVOH/3.0 wt.% SWCNTs (Fig.4c), and the ternary hybrid HAVOH/3.0 wt.% SWCNTs/1.0 wt.% MXenes (Fig.4d) are presented. All composites reveal a homogeneous morphology. When 2D MXene nanofiller was added to HAVOH, the formation of lamellar filler structures parallel to the sample surface was observed. This can be attributed to the MXene layered structure. For the binary HAVOH/3.0 wt.% SWCNTs (H/3 SWCNTs) sample (Fig.4c), instead of ordered lamellar structures, well dispersed SWCNTs without large agglomerates are observed. As a result of mixing of 1D and 2D nanofillers, such as for the sample HAVOH/3.0 wt.% SWCNTs/1.0wt.% MXenes (H/3 SWCNTs/1 MX) (Fig.4d), a combination of individual structures of binary composites with utilized fillers is observed. In particular, either lamella structures typical of MXenes or well-dispersed SWCNTs that are able to connect MXene lamellae are observed. Thus, improving the electrical conductivity of the samples by the creation of continuous conductive pathways is present. Further insights into the dispersion and orientation of the filler within the HAVOH matrix were provided with TEM analysis. TEM micrographs of the binary and ternary composites are shown in Fig.5 and additional photos can be found in SI (Fig.S3). Figure5a shows a bright-field TEM micrograph of H/3 MX composite sample with 3.0 wt.% of 2D MXenes, with a well-demonstrated layered structure attributed to the alignment of MXene lamellae to the surface of the film, confirming what was already evidenced by SEM analysis. MXene lamellae are tightly packed with each other with regular morphology. For the HAVOH/3.0 wt.% SWCNTs binary composite (Fig.5b), CNT bundles can be clearly observed. They have a loose structure, which is evidenced in the micrograph as gray/black halos, because single nanotubes cannot be resolved due to their very low diameter. When the two fillers were combined together, a continuous net of hybrid MXenes/SWCNTs was observed (Fig.5c). SWCNTs, in this case also evidenced as low-contrast bundles in comparison to high-atomic-number MXenes, contribute to the connection of the MXene lamellae, which clearly indicates the formation of 3D hybrid conductive pathways within the nanocomposite structure that are responsible for the improved electrical conductivity. For this sample, the highly regular spatial arrangement of MXene lamellae evidenced for the binary HAVOH/MXene composite is partially lost as the arrangement of the lamellae is perturbed and hindered by the copresence of SWCNTs. HAVOH-based samples were analyzed with BDS to study their electrical properties. Figure6 shows a plot of the measured conductivities of the binary and ternary HAVOH composites. The neat matrix with a σDC ′ conductivity value of 6 × 10–12 S/cm had a typical insulator response. For the composite with 2.0 wt. % MX, the conductivity increased to approximately 2 × 10–9 S/cm; beyond a critical frequency (fc), a power law followed, whereas for f < fc, σ′ exhibited a plateau, corresponding to DC conductivity ( σDC ′ )39. The addition of 2.0wt.% MXenes to HAVOH slightly increases σDC ′ conductivity, reaching 2 × 10–9 S/cm, while the composite sample Figure3. Chemical structure of (a) PVOH and (b) HAVOH. 7 Vol.:(0123456789) Scientific Reports | (2023) 13:19126 | https://doi.org/10.1038/s41598-023-46083-2 www.nature.com/scientificreports/ with 1.0wt.% of this filler has a similar curve shape (similar fc) and very close values to the neat matrix. The specimen with 1.0 wt.% of SWCNTs is on the same order range with a conductivity of 7.5 × 10–7 S/cm. Hybrid ternary composites, HAVOH/3.0 wt.% SWCNTs/1.0 wt.% MXenes and HAVOH/3.0 wt.% SWCNTs/2.0 wt.% MXenes, together with binary composite HAVOH/3.0wt.% SWCNTs in between, are reaching more than two times better conductivity compared to the HAVOH matrix alone. Their σDC ′ conductivity values, 5.2 × 10–5, 6.1 × 10–5 and 7.9 × 10–5 S/cm, respectively, are the highest among all fabricated HAVOH samples. The percolation threshold for HAVOH binary composites was calculated using the equation and scaling law: where σDC is the DC conductivity, pc is the percolation threshold, p is the volume fraction of the filler, and t is the exponent characterizing the dimensionality of the investigated conductive system. In HAVOH/SWCNTs, pc is 0.7 vol.%, which corresponds to 1.0 wt. %. For samples with MXenes filler, pc was 0.56 vol.%, which in weight percentage is equal to 1.4 wt.%. As shown in this plot, the electrical conductivity of HAVOH-based composites did not exceed 8 × 10–5 S/cm. This is just one order of magnitude from values of 1.2×10-4 S/cm for HAVOH/6.0 wt. % MWCNT presented by Santillo etal.5. So, with slightly lower filler content 4 (3 wt.% SWCNTs + 1 wt.% MX) and 5 (3 wt.% SWCNTs + 2 wt.% MX) wt. % we achieved a very good conductive network penetrated into the HAVOH matrix without using any additional surfactant, as was the case of Santillo etal5. The EMI shielding properties for the neat HAVOH matrix as well as for nanocomposites with SWCNTs and MXene fillers in the frequency range from 8.2 to 12.4GHz (X-band) were first determined and expressed by the S21 parameter. According to Fig.7, the HAVOH matrix’s transparency in a given region is approximately 92%, i.e., its shielding efficiency in a composite without nanoparticles is approximately S21 = -0.45dB, which is negligible. Parameter S11 for all composites indicates the high conductivity of the samples, and S11 approaches zero. The shielding efficiency S21 for composites with 1.0 wt.% SWCNTs exhibit increasing shielding (−35dB), while the sample with 3 wt.% of SWCNTs exhibits worse shielding, namely, −25dB. This is possibly caused by the poor quality of the sample, which is macroscopically irregular, with some holes and defects due to the high amount of SWCNTs. Shielding of samples with 1.0 and 3.0 wt.% of MXenes exhibits good shielding (−10 and −15dB). Better results are obtained for samples containing both fillers (SWCNTs and MXenes), which exhibit great shielding (8) σDC ≈  p−p ct, Figure4. SEM images of (a) neat H, (b) H/1 MX, (c) H/3 SWCNTs; and (d) H/3 SWCNTs/1 MX. 8 Vol:.(1234567890) Scientific Reports | (2023) 13:19126 | https://doi.org/10.1038/s41598-023-46083-2 www.nature.com/scientificreports/ Figure5. TEM images of (a) H/3 MX; (b) H/3 SWCNTs; and (c) H/3 SWCNTs/3 MX. Figure6. Dependency of real part of HAVOH/SWCNTs, HAVOH/MXenes, and HAVOH/SWCNTs/MXenes composite samples conductivities on frequency. 9 Vol.:(0123456789) Scientific Reports | (2023) 13:19126 | https://doi.org/10.1038/s41598-023-46083-2 www.nature.com/scientificreports/ of −40dB (HAVOH/3.0 wt.% SWCNTs/1.0 wt.% MXenes) and −55dB (HAVOH/3.0 wt.% SWCNTs/3.0 wt.% MXenes), which is much higher than the sample with 3.0 wt.% SWCNTs. This confirms that MXenes helpto form a compact conductive network together with the SWCNTs and improve their EMI-shielding. The morphology study showed that MXene has a lamellar structure and the well-dispersed SWCNTs formed a continuous conductive path between the lamellae. Thus, improving the electrical conductivity in composites HAVOH/ SWCNTs/MXenes is proof of that. Actually, a material absorbs EM waves and converts them into heat, and this conversion ability is determined by the conduction loss and the polarization loss. Polarization loss has an important contribution to the absorption of EM waves. In fact, the defects formed during the etching process as was introduced by Peng He etal.40 lead to the asymmetry in the spatial distribution of electrons to form dipole moments. Moreover, terminal atoms attached on the surface of MXenes (Fig.S1) lead to the asymmetric distribution of charge density, which in-turn causes the formation of dipoles. Under an alternating electromagnetic field, these dipoles will break loose and rotate directionally. When their rotation cannot keep up with the change in EM field, polarization relaxation occurs with EM energy loss. Recent researchers have mainly focused on the EMI shielding performance of Ti3C2Tx MXene films31. However, EM waves are mostly reflected by high conductivity in the Ti3C2Tx film and this behavior is the same as a metal shielding the EM wave. Only a small amount of EM waves can enter the body of films and be absorbed. Compared with the MXene films that mainly use high conductivity to reflect EM waves, the composites made by dispersing the SWCNTs and MXene into the HAVOH matrix can reduce the conductivity and absorb more EM waves by polarization loss. This means that more EM waves can be attenuated so that secondary reflections will be effectively reduced, demonstrating their environmentally friendly performance. Figure8 shows the split of total shielding into absorption and reflection parts and provides another view of the shielding efficiency of HAVOH/SWCNTs/MXene morphologies. The reflectivity of all composites is quite similar, with values in the range of 7–15dB. More interesting is the absorption of the samples, which show large differences among the samples. The samples filled with MXenes absorb much less than the samples filled with SWCNTs, which absorb up to 45dB. The contribution of reflection and absorption can also be viewed in Table3 and Fig.S4. Visualizing the proportion between the three components in “RAT analysis” (analysis of reflection, absorption, and transmission capability of each sample) clearly indicates higher absorption percentage of samples with MXene/SWCNTs hybrid structure. The results obtained in this work were compared with other reported values of the shielding effectiveness of MXene composites. Miao etal.41 obtained 54.7dB of RLmin (extreme reflection loss) for the MoS2/TiO2/Ti2CTx sample. This value is the closest to that reported here; however, the sample thickness is three times higher than our HAVOH/3.0 wt.% SWCNTs/3.0 wt.% MXenes. Additionally, the filler ratio that has to be used is high, reaching 70 wt.%, which is almost 12 times more than for our specimen with a total filler load of 6 wt.%. Gao etal.42 also received high SE values. Prepared composite with thermoplastic polyurethane as a matrix and MXenes filler showed 50.7dB, but high amount of filler load such as 28.6 wt.% had to be admixed. HAVOH composites showed great shielding effectiveness. When comparing the neat polymer matrix and the composite sample that showed the best results, namely, HAVOH/3.0 wt.% SWCNTs/3.0 wt.% MXenes, the difference is more than 100 times. This indicates that utilization of both fillers in relatively small amounts and a very good synergistic effect greatly increases reflection and absorption and decreases transmission of electromagnetic interference, thus creating a great barrier. These results are promising for further development of EMI-shielding films or devices. To study thermal behavior of the specimens differential scanning calorimetry and thermogravimetric analyses were used. DSC thermograms of pristine HAVOH and HAVOH-based composite samples, recorded during cooling from the melt and successive heating of the melt-crystallized samples, are shown in Fig.6. Values of glass transition temperatures (Tg), melting temperatures (Tm) and melting enthalpy (ΔHm) are summarized in Table2. As shown, the DSC heating curve of pristine HAVOH, crystallized from the melt at 10C/min, displays a Tg of 75.5°C, a Tm of 199.2°C and a ΔHm of 34.2J/g (Fig.9 and Table2). For binary composites containing 8.0×10 9 9.0×10 9 1.0×10 10 1.1×10 10 1.2×10 10 1.3×10 10 -15.0 -13.5 -1.5 0.0 1.5 S 11 (dB) Frequency (Hz) H/3 MX H/1 SWCNTs Neat HAVOH H/3 SWCNTs/1 MX H/3 SWCNTs/3 MX H/3 SWCNTs H/1 MX a) 8.0×10 9 9.0×10 9 1.0×10 10 1.1×10 10 1.2×10 10 1.3×10 10 -60 -50 -40 -30 -20 -10 0 S 21 (dB) Frequency (Hz) Neat HAVOH H/1 MX H/1 SWCNTs H/3 SWCNTs/3 MX H/3 SWCNTs/1 MX H/3 SWCNTs H/3 MX b) Figure7. EMI-shielding efficiency expressed (a) by S11 parameter of the samples, and (b) by S21 parameter of the samples.