The valorization of end-of-life (EoL) photovoltaic (PV panels) waste through its incorporation as a particulate filler in epoxy resin composites was investigated, with focus on the resulting dielectric properties. The main scope of this work is to turn waste from whole EoL PV panels into a useful product through a simple process. Following a size reduction with milling, samples from three different types of EoL PVs (CIS, CIGS, c-Si) were used as filler particles in a Resoltech 1050 epoxy resin system with concentrations 0, 2.5, 5, 7.5 and 10% w/w. Mechanical and dielectric properties of the composite materials were evaluated through bending, shearing tests, Dynamic Mechanical Analysis (DMA) and Broadband Dielectric Spectroscopy (BDS). The responses from five different samples (CIS, CIGS, c-Si, silicon solar cells and Glass) were compared. It was shown that resin reinforced with 2.5% PV panels waste of any type had similar or better response in mechanical properties compared to the neat epoxy resin. The BDS characterization highlighted interfacial polarization and alpha, beta-relaxation phenomena of the composites in a temperature range of 30 degrees C-120 degrees C and frequencies of the applied external field from 10-1 to 107 Hz. The calculated energy density U indicates that addition of 2.5% w/w EoL PV panels particles increased the ability to store energy of the matrix by up to 25% at 30 degrees C, while at higher temperatures it increased the ability of the matrix up to 45 times. PV panels waste particles can achieve a new and effective role as reinforcing filler for polymer composites at a low cost.

Nanocomposites consisting of titanium carbonitride nanoparticles (TiCN) and epoxy resin were fabricated and studied as the filler content was varied. Nanocomposites' structural investigation was conducted via X-ray Diffraction technique (XRD), while their morphology was examined by employing Scanning Electron Microscopy (SEM). Viscoelastic mechanical properties were assessed by Dynamic Mechanical Thermal Analysis (DMTA). Results revealed the reinforcing ability of TiCN nanoparticles. The dielectric characterization of the nanocomposites was carried out using Broadband Dielectric Spectroscopy (BDS) over a wide frequency and temperature range. Dielectric spectroscopy revealed two relaxation processes related to the polymer matrix: the alpha-relaxation, associated with the glass-to-rubber transition, and the beta-relaxation, associated with the rearrangement of side polar groups. In addition, in the low-frequency-high-temperature region, interfacial polarization (IP) was observed. IP is related to the presence of nanoparticles and to the accumulation of unbound charges at the system's interface and includes contributions from a dipolar process and charge migration (conductivity). Alternating current conductivity generally increases with filler content, though it is also affected by frequency and temperature. Conductivity could influence Electrode Polarization (EP), which often masks the dipolar process of IP. A simple method for removing the EP effect is formulated and tested.

In this study, epoxy resin sheets were cured by embedding Kanthal D resistance wires and applying Joule heating. The temperature developed by the embedded Kanthal wires remained constant for various curing times of up to 24 h. The degree of curing (DOC) via DSC experiments was determined, revealing that specimens closer to the heating element cured 15 h faster. The dynamic viscoelastic behavior of the epoxy resin via DMA was studied as a function of both the curing time and the point distance from the heating element. It was concluded that the epoxy resin located at a significant distance from the Kanthal wire will never reach a fully cured condition, despite receiving heat from the heating element. Thermal images were captured during the Joule heating curing process to simultaneously provide the temperature distribution variation with location and time. The experimentally obtained temperature distribution was then predicted and compared with respective numerical results. Finally, to determine the ideal distance between Kanthal wires, the separation distance between them was parametrized following the validation of the numerical model. The optimized separation distance of the Kanthal wires, according to the numerical analysis, was found to be 3 mm, at a constant applied temperature of 53 degrees C.Highlights Complete curing of an epoxy resin sheet using only SRE heating. DOC studied with respect to topological, temporal, and temperature variables. Experimental results predicted/validated by corresponding numerical results. Validated numerical models utilized for optimal distance of heating elements.

In this work magnetic nanoparticles (Fe3O4, or ZnFe2O4, or SrFe12O19) and BaTiO3 microparticles were embedded in an epoxy resin for the synthesis of three series of hybrid magnetic polymer nanocomposites. Barium titanate content was kept constant, while magnetic phase content was varied. Fabricated specimens were structurally and morphologically characterized by employing scanning electron microscopy images and X-ray diffraction patterns. Results implied successful synthesis of the hybrid nanocomposites. The magnetic behavior of the pure magnetic nanoparticles and the fabricated nanocomposites was investigated via a Vibrating Sample Magnetometer. The magnetic performance of each type of magnetic phase (i.e., soft and hard) was induced in the nanocomposites, and magnetic performance is strengthened with the increase in magnetic phase content. Initial magnetization curves were used for the determination of mass magnetic susceptibility of all nanocomposites. Magnetic saturation and magnetic remanence have been found to follow a linear relationship with magnetic phase content, giving the opportunity to predict the system’s response in advance.

Polymer-based hybrid composites have emerged as promising platforms for multifunctional energy applications, combining structural versatility with tunable dielectric behavior. In this study, synthesized [Fe(bpy)3]SO4; (tris(2,2′-bipyridine)iron(II) sulfate) coordination compound was incorporated into a green epoxy resin matrix to fabricate nanocomposites aimed at enhancing dielectric permittivity (ε′), piezoelectric coefficient (d33, pC/N), energy-storage efficiency (nrel, %), and mechanical strength (σ, MPa). The integration of the Fe(II) complex via Scanning Electron Microscopy (SEM) confirmed a homogeneous dispersion within the matrix. Broadband Dielectric Spectroscopy (BDS) revealed the presence of three relaxation processes in the spectra of the tested systems, demonstrating enhanced dielectric permittivity with increasing Fe(II) content. Under progressively shorter relaxation times (τ, s), key processes such as interfacial polarization, the polymer matrix’s transition from a glassy to a rubbery state, and the dynamic reorganization of polar side groups along the polymer backbone are activated. The ability to store and retrieve electric energy was confirmed by varying filler content under direct current (dc) conditions. The nanocomposite with 10 phr (mass parts/100 mass parts of resin) filler achieved a piezoelectric coefficient of d33 = 5.1 pC/N, an energy-storage efficiency of nrel = 44%, and a tensile strength of σ = 55.5 MPa, all of which surpass values reported for conventional epoxy-based composites. These results confirm the ability of the system to store and retrieve electric energy under direct current (dc) fields, while maintaining mechanical robustness and thermal stability due to synergistic interactions between the epoxy matrix and the Fe(II) complex. The multifunctional behavior of the composites underscores their potential as advanced materials for integrated dielectric, piezoelectric, and energy storage and harvesting applications.

In the present work, hybrid nanocomposites of an epoxy resin reinforced with ZnTiO3 and BaTiO3 nanoparticles, at various filler contents, were fabricated and studied. The successful integration of ceramic nanofillers and the fine distribution of nanoparticles were confirmed via X-ray Diffraction patterns and Scanning Electron Microscopy images, respectively. Dielectric properties and related relaxation phenomena were investigated via Broadband Dielectric Spectroscopy in a wide range of frequencies and temperatures. Data analysis showed that dielectric permittivity increases with filler content, although optimum performance does not correspond to the maximum ZnTiO3 content. Four relaxation processes were observed and attributed to interfacial polarization (IP) (at low frequencies and high temperatures), glass-to-rubber transition (α-relaxation) of the epoxy matrix (at intermediate frequencies and temperatures), and local rearrangements of polar side groups of the macromolecules (β-relaxation) and small flexible groups of the main polymer chain (γ-relaxation) occurring at low temperatures and high frequencies. The ability of hybrid nanocomposites to store and retrieve energy was studied under dc conditions by employing a charging/discharging sequence. The stored and retrieved energy increases with filler content and charging voltage. The optimum ability of energy recovering, shown by the epoxy/7 phr ZnTiO3/7 phr BaTiO3 nanocomposite, ranges between 30 and 50 times more than the matrix, depending on the time instant. The employed nanoparticles induce piezoelectric properties in the nanocomposites, as found by the increase in the piezoelectric coefficient with filler content.

In this work, the effect of etching the surface of polymer matrix nanocomposites with atmospheric pressure plasma targeting to achieve enhanced dielectric properties was investigated. Polymer nanocomposites, with varying reinforcing phase content, were modified by atmospheric-pressure plasma resulting in an increase in the surface filler’s concentration. Polymethyl methacrylate (PMMA) matrix nanocomposites reinforced with zinc oxide (ZnO) nanoparticles were prepared and dielectrically studied as a function of the nanoparticle content and the plasma modified surfaces. The electrical response of the composite systems was studied by means of Broadband Dielectric Spectroscopy (BDS) over a wide range of temperatures and frequencies. The dielectric permittivity increased with the embedded phase content and with plasma surface treatment. Energy density followed the same trend as dielectric permittivity, and the plasma-treated nanocomposite with the higher ZnO content exhibited approximately 27% higher energy density compared to the unreinforced matrix.

In the present work, carbonate minerals are added in non-polar and polar polymer matrices to develop halogen-free flame-retardant composites. The examined fillers of calcium carbonate and magnesium carbonate delivered improved rheological performance in both non-polar (PE) and polar (EVA/PE) polymer compounds compared to the natural magnesium hydroxide and huntite/hydromagnesite mineral fillers. The presence of EVA in the matrix enhanced the mechanical behavior of all compounds in tensile testing. The thermal stability of the composites was particularly improved for the polar systems with the incorporation of the carbonate minerals, as this was evidenced under thermogravimetric analysis. The dielectric behavior of the fabricated systems was examined via broadband dielectric spectroscopy. The HFFR compounds attained higher values of the real part of dielectric permittivity from the unreinforced systems in the whole frequency and temperature range of the conducted tests. This behavior is ascribed to the higher permittivity values of the fillers with respect to the polymer matrices and the occurrence of interfacial polarization. All minerals improved the flame retardancy of the compounds in terms of LOI values, while the addition of EVA yielded further improvements, especially for the magnesium carbonate and the magnesium hydroxide minerals.

3D-printed biomedical polylactic acid (PLA) scaffolds were developed, and their biodegradation, as well as their thermomechanical behavior, were studied in a relevant in vitro environment. The scaffold’s biodegradability profile has been monitored after immersion in a cell culture medium that contains components of blood and body fluids. Two types of biodegradation experiments were performed—a standard static one and an adapted stirring one, mimicking the body fluids’ flow, respectively—to achieve a comparative investigation. The biodegradation experiment’s duration was one month. The measurements were performed between days 1 and 28. The scaffold microstructure was analyzed with scanning electron microscopy (SEM). The weight loss of the scaffolds has been monitored. Differential scanning calorimetry (DSC) has been used to evaluate the glass transition temperature (Tg) of the scaffolds and to draw useful conclusions about their thermal behavior. Finally, dynamic mechanical analysis (DMA) was applied to investigate the viscoelastic behavior of the samples. The SEM analysis demonstrated that the samples in a static experiment are more damaged, while those in the stirring experiment are more brittle. The maximum Tg value of the material measured by DSC is around 65 °C. This value is reached after 5 days of immersion in static conditions and after 14 days of immersion after stirring, indicating that some processes take place faster in the static experiment. The variation of the Tg vs. immersion time, as derived from DSC vs. DMA measurements, gives similar results for both static and fluid absorption conditions, demonstrating the reproducibility of the results.

The aim of this study is to use fly ash powder in an environmentally friendly matrix, in a novel way, addressing environmental and disposal problems. Fly ash/epoxy composites were prepared and studied varying the filler content. An investigation of structural and morphological characteristics was conducted using of X-ray diffraction patterns and scanning electron microscopy images, which revealed the successful fabrication of composites. Thermomechanical properties were studied via dynamic mechanical analysis and static mechanical tests. The composites exhibited an improved mechanical response. Broadband dielectric spectroscopy was used to investigate the dielectric response of the composite systems over the frequency range from 10−1 to 107 Hz and the temperature range from 30 to 160 °C. The analysis revealed the presence of three relaxation processes in the spectra of the tested systems. Interfacial polarization, the glass-to-rubber transition of the polymer matrix, and the rearrangement of polar side groups along the polymer chain are the processes that occur under a descending relaxation time. It was found that dielectric permittivity increases with filler content. Finally, the influence of filler content and the applied voltage under dc conditions was analyzed to determine the ability of the composites to store and retrieve electric energy. Fly ash improved the efficiency of the storing/retrieving energy of the composites.

This study outlines a method for the epoxidation of poly-beta-myrcene, a biopolymer that can be easily extracted from the natural resin of the Chios Mastic tree (Pistacia lentiscus L.). The resulting epoxidation products are self-curing, and have a nearly 100% green carbon content. These Mastic Epoxide products (MASTEP) have the potential to be useful thermosetting resins. One specific product (MASTEP A), was used as an adhesive to create Single Lap Joints, which were then subjected to tensile shear stress tests. MASTEP A was found to be 25%-83% stronger than three commonly used conventional or "semi-green" epoxy adhesives. Another specific product (MASTEP B), was found able to be thermally converted into a semi-crystalline form. In order to clarify the 3D chemical structure of MASTEP, IR, and DSC investigations were conducted. The entire production process was designed to be environmentally friendly. The results of this research represent a significant advancement in the development of environmentally friendly epoxies and pave the way to a wide range of potential further research.

The prospect of using recovered solar cells from end-of-life (EoL) photovoltaic panels (PVPs) to produce composite materials with dielectric properties was studied. The main goal of this research was to reduce the waste originating from EoL PVPs by reusing the semiconductor, thus rendering solar energy an even greener energy source. Solar cells were recovered from EoL PVPs through thermal treatment to remove polymer sheets and screening to separate the solar cells from glass and electrodes. Composite materials were manufactured by reinforcing two different epoxy resins, Araldite LY556 and Resoltech 1050, with varying concentrations of ground solar cells (0–10% w/w). The mechanical and dielectric properties of the composite materials were examined with bending and shearing tests and Broadband Dielectric Spectroscopy (BDS), respectively. The responses from the two different resin matrices were compared. It was found that the produced composite material resulting from Resoltech resin reinforced with solar cells recovered from EoL PVPs had better mechanical and dielectric properties. BDS characterization of the composite materials indicated that the solar cells can be used to enhance the energy storage capacity of the polymeric matrix and thus may be potentially used in the manufacturing of capacitors. Graphical Abstract

Polymer matrix nanocomposites are widely studied because of the versatility of their physical and mechanical properties. When these properties are present simultaneously, responding at relative stimuli, multifunctional performance is achieved. In this study, hybrid nanocomposites of SrFe12O19 and BaTiO3 ceramic particles dispersed in an epoxy resin matrix were fabricated and characterized. The content of SrFe12O19 was varying, while the amount of BaTiO3 was kept constant. The successful fabrication of the nanocomposites and the fine dispersion of the ceramic particles was verified via the morphological and structural characterization carried out with X-ray Diffraction patterns and Scanning Electron Microscopy images. Dielectric response and related relaxation phenomena were studied by means of Broadband Dielectric Spectroscopy. Dielectric permittivity augments with filler content, while the recorded relaxations, with descending relaxation time, are: (i) interfacial polarization, (ii) glass-to-rubber transition, (iii) intermediate dipolar effect, and (iv) re-orientation of polar-side groups of the main polymer chain. SrFe12O19 nanoparticles induce magnetic properties to the nanocomposites, which alter with the magnetic filler content. Static and dynamic mechanical response improves with filler content. Thermogravimetric analysis shown that ceramic particles are beneficial to the nanocomposites’ thermal stability. Glass transition temperature, determined via Differential Scanning Calorimetry, was found to slightly vary with filler content, in accordance with the results from dynamic mechanical and dielectric analysis, indicating the effect of interactions occurring between the constituents. Examined systems are suitable for energy storing/retrieving.

In this study, hybrid boron nitride (BN)/titanium carbide (TiC)/epoxy resin composite nanodielectrics were manufactured and characterized. Their morphological and structural characterization was conducted via scanning electron microscopy (SEM) images and X-ray diffraction (XRD) patterns, whereas the dielectric behavior was studied by means of broadband dielectric spectroscopy (BDS). Dielectric measurements were carried out from 30 to 160 °C and from 10−1 to 106 Hz, respectively. The dielectric results revealed the existence of three relaxation mechanisms, which from high to low frequencies, at constant temperature, refer to re-arrangement of polar-side groups (β-relaxation) of the macromolecular chains, transition from glassy to rubbery state of the amorphous polymer matrix (α-relaxation) and interfacial polarization (IP) between the polymer matrix and the nanofillers. It was found that, in general, nanodielectrics exhibited enhanced dielectric properties mainly due to the high dielectric permittivity of TiC and the fine dispersion of the fillers, confirmed also by the SEM images. Dynamic analysis conducted for the α-relaxation showed a Vogel–Fulcher–Tammann dependence on temperature. The ability of energy storing of the nanocomposites was examined via their energy density. Optimum performance is exhibited by the 5 phr TiC/1 phr BN/epoxy nanocomposite, reaching an energy storing ability nine times greater than the unfilled matrix.

In this work, UV-curable resin poly (ethylene glycol) diacrylate (PEGDA) was reinforced with three different types of nanofillers: pristine graphene (G), multiwalled carbon nanotubes (MWNTs), and a hybrid of MWNTs and graphene 70/30 in mass ratio (Hyb). PEGDA was mixed homogenously with the nanofiller oligomer by shear mixing and then photopolymerized, affording thin, stable films. The thermomechanical properties of the afforded nanocomposites indicated the superior reinforcing ability of pristine graphene compared with MWNTs and an intermediate behavior of the hybrid.

Epoxy/BaTiO3 nanocomposites developed at low nanofiller concentrations with their dielectric relaxations, charge transport dynamics and capacitive energy storage were investigated via dielectric spectroscopy and dc charge-discharge experiments. Two relaxation processes were observed, namely the alpha- and beta-relaxations, attributed to the dynamic T-g process and local motions, respectively. Another process located at low frequencies and high temperatures was identified as interfacial polarization. The charge transport properties were examined via the ac conductivity and impedance formalisms, indicating a beneficial effect with the increase of the nanofiller content. The dc conductivity was calculated from the ac spectra and exhibited Arrhenius temperature dependence. The theoretical energy density was found to increase up to 3.5 times comparing to the neat epoxy resin, highlighting the reinforcing dielectric/capacitive effect of the BaTiO3 nanoparticles on the epoxy resin. Comparisons between the theoretical energy densities and experimentally determined values were also discussed in detail.

In this study, hybrid nanocomposites consisting of Fe3O4/BaTiO3/epoxy resin were prepared with varying amounts of filer content. Structural and morphological characterization, conducted via X-Ray Diffraction patterns and Scanning Electron Microscopy images, revealed the successful fabrication of composites and fine dispersion of inclusions. Thermomechanical properties are studied via Differential Scanning Calorimetry, Thermogravimetric Analysis, Dynamic Mechanical Analysis and static mechanical tests. Hybrid composites exhibit enhanced thermal stability and improved mechanical response. Indicatively, Young’s modulus, tensile strength and fracture toughness increase from 1.26 GPa, 22.25 MPa, and 3.03 kJ/m3 for the neat epoxy to 1.39 GPa, 45.73 MPa, and 41.08 kJ/m3 for the composites with 20 or 15 parts per hundred resin per mass (phr) of Fe3O4, respectively. Electrical behavior is investigated via Broadband Dielectric Spectroscopy and ac conductivity measurements. The real part of dielectric permittivity reaches the value of 11.11 at 30 °C for the composite with 40 phr of Fe3O4. The ability to store and retrieve electric energy on the nanocomposites is examined with the following parameters: the filler content and the applied voltage under dc conditions. Retrieved energy reaches 79.23% of the stored one, for the system with 15 phr of Fe3O4. Magnetic response is studied via a Vibrating Sample Magnetometer. Magnetic saturation, for the system with the highest magnetic filler content, obtains the value of 25.38 Am2/kg, while pure magnetic powder attains the value of 86.75 Am2/kg. Finally, the multifunctional performance of the nanocomposites is assessed regarding all the exerted stimuli and the optimum behavior is discussed.

Bone substitute materials are placed in bone defects and play an important role in bone regeneration and fracture healing. The main objective of the present research is fabrication through the technique of 3D printing and the characterization of innovative composite bone scaffolds composed of polylactic acid (PLA), poly (ε-caprolactone) (PCL) while hydroxyapatite (HAp), and/or barium titanate (BaTiO3—BT) used as fillers. Composite filaments were prepared using a single screw melt extruder, and finally, 3D composite scaffolds were fabricated using the fused deposition modeling (FDM) technique. Scanning electron microscopy (SEM) images showed a satisfactory distribution of the fillers into the filaments and the printed objects. Furthermore, differential scanning calorimetry (DSC) measurements revealed that PLA/PCL filaments exhibit lower glass transition and melting point temperatures than the pure PLA filaments. Finally, piezoelectric and dielectric measurements of the 3D objects showed that composite PLA/PCL scaffolds containing HAp and BT exhibited piezoelectric coefficient (d33) values close to the human bone and high dielectric permittivity values.

Epoxy resins are, probably, the most used polymers as matrices for composites in high-tech applications. Epoxy resins are typical insulating materials being able to be polarized under the influence of an external electric field. With the application of alternating current field, dielectric relaxations take place in epoxy resins, related to segmental motion of parts of polymer chains and localized motions of polar side groups and small parts of the macromolecules. Moreover, their limited concentration of free charge carriers keeps the conductivity values low. Epoxy resins can be reinforced via non-conductive and conductive fillers such as oxides, organic compounds, carbides, nitrides, metals, and carbon allotropes. The shape of the fillers could vary significantly including spheroids, flakes, needles, or long fibers. In micro- and nano-epoxy composites, an additional dielectric relaxation effect is present, known as interfacial polarization or Maxwell–Wagner–Sillars effect, because of the accumulation of free charges at the composites' interface and the heterogeneity of the systems. The electrical performance (dielectric response and conductivity) of epoxy-based composites can be tuned by controlling the type, the amount, and the distribution of the employed filler or fillers. Dielectric and conductivity studies provide valuable information concerning the physical origin of molecular motions, interfacial effects, phase changes, charge transport mechanisms, and interactions between constituents. The inherent properties of epoxy resins, such as flexibility, thermomechanical stability, resistance to chemical attack, and light weight combined with the filler-induced electrical behavior and the ability of the composites to store and retrieve electrical energy lead to systems with multifunctional performance.

Compact capacitive energy storing/harvesting systems could play a key role in the urgent need for more energy-efficient technologies to address both energy and environmental issues. Therein, the purpose of the present work is to develop and investigate epoxy/BaMnO4 nanocomposites at various filler concentrations, which could be applicable as compact materials systems for energy storage and harvesting. Broadband dielectric spectroscopy was used for studying the dielectric properties and the relaxation processes of the examined nanodielectrics. The energy storing/retrieving ability of the nanocomposites was also evaluated via DC charge–discharge experiments. The coefficient of energy efficiency (neff) was found for all prepared nanocomposites to evaluate the energy performance of the systems. Dielectric data divulge the existence of two matrix-related relaxations, i.e., α-mode and β-mode, attributed to the glass-to-rubber transition of the polymer matrix and re-orientation of polar side groups, respectively. Interfacial polarization was also identified in the low-frequency and high-temperature region. The 7 phr BaMnO4 nanocomposite exhibits the best performance in terms of the stored and harvested energies compared to all systems. On the other hand, the 5 phr, 3 phr and 1 phr nanocomposites display optimum energy performance, reaching high values of neff.