Search

Currently, the epoxy resin market is expressing concerns about epoxy resins’ non-recyclability, which can hinder their widespread use. Moreover, epoxy monomers are synthesized via petroleum-based raw materials, which also limits their use. So, it is crucial to find more environmentally friendly alternative solution for their formulation. Within this context, the aim of this paper is to exploit a Cradle-to-Cradle approach, which consists of remodeling and reshaping the productive cycle of consumer products to make sure that they can be infinitely reused rather than just being recycled with a downgrading of their properties or uses, according to the principle of the complete circular economy. Indeed, after starting with a fully-recyclable bio-based epoxy formulation and assessing its recyclability as having a process yield of 99%, we obtained a recycled polymer that could be reused, mixing with the same bio-based epoxy formulation with percentages varying from 15 wt% to 27 wt%. The formulation obtained was thoroughly characterized by a dynamic-mechanical analysis, differential scanning calorimetry, and flexural tests. This approach had two advantages: (1) it represented a sustainable disposal route for the epoxy resin, with nearly all the epoxy resin recovered, and (2) the obtained recycled polymer could be used as a green component of the primary bio-based epoxy matrix. In the end, by using replicated general factorial designs (as statistical tools) combined with a proper optimization process, after carrying out a complete thermo-mechanical characterization of the developed epoxy formulations, the right percentage of recycled polymer content was selected with the aim of identifying the most performing epoxy matrix formulation in terms of its thermo-mechanical properties.

Fused filament fabrication is a technology of additive manufacturing that uses molten thermoplastics for building parts. Due to the convenient shape of the raw material, a simple filament, the market offers a great variety of materials from simple to blends of compatible materials. However, finding a material with the desired properties can be difficult. Making it in-house or using a material manufacturer can be costly and time-consuming, especially when the optimum blend ratios are unknown or new design perspectives are tested. This paper presents an accessible method of producing core-shell filaments using material extrusion 3D printing. The printed filaments are characterised by a polycarbonate (PC) core and acryl butadiene styrene (ABS) shell with three material ratios. Their performance was investigated through printed samples. Additionally, the material mixing degree was studied by varying the extrusion temperature, nozzle feeding geometry, and layer thickness. The influence of all four factors was evaluated using a graphical representation of the main effects. The results showed that a core-shell filament can be processed using a 3D printer with a dual extrusion configuration and that the mechanical properties of the samples can be improved by varying the PC–ABS ratio. This research provides an accessible method for developing new hybrid filaments with a predesigned structure using a 3D printer.

This article’s objective is the synthesis of new composites based on thermoplastic polyurethane (TPU) and TiO2 nanowires (NWs) as free-standing films, highlighting their structural and optical properties. The free-standing TPU–TiO2 NW films were prepared by a wet chemical method accompanied by a thermal treatment at 100 °C for 1 h, followed by air-drying for 2 h. X-ray diffraction (XRD) studies indicated that the starting commercial TiO2 NW sample contains TiO2 tetragonal anatase (A), cubic Ti0.91O (C), and orthorhombic Ti2O3 (OR), as well as monoclinic H2Ti3O7 (M). In the presence of TPU, an increase in the ratio between the intensities of the diffraction peaks at 43.4° and 48° belonging to the C and A phases of titanium dioxide, respectively, is reported. The increase in the intensity of the peak at 43.4° is explained to be a consequence of the interaction of TiO2 NWs with PTU, which occurs when the formation of suboxides takes place. The variation in the ratio of the absorbance of the IR bands peaked at 765–771 cm−1 and 3304–3315 cm−1 from 4.68 to 4.21 and 3.83 for TPU and the TPU–TiO2 NW composites, respectively, with TiO2 NW concentration equal to 2 wt.% and 17 wt.%, indicated a decrease in the higher-order aggregates of TPU with a simultaneous increase in the hydrogen bonds established between the amide groups of TPU and the oxygen atoms of TiO2 NWs. The decrease in the ratio of the intensity of the Raman lines peaked at 658 cm−1 and 635 cm−1, which were assigned to the vibrational modes Eg in TiO2 A and Eg in H2Ti3O7 (ITiO2-A/IH2Ti3O7), respectively, from 3.45 in TiO2 NWs to 0.94–0.96 in the TPU–TiO2 NW composites, which indicates that the adsorption of TPU onto TiO2 NWs involves an exchange reaction of TPU in the presence of TiO2 NWs, followed by the formation of new hydrogen bonds between the -NH- of the amide group and the oxygen atoms of TixO2x-mn, Ti2O3, and Ti0.91O. Photoluminescence (PL) studies highlighted a gradual decrease in the intensity of the TPU emission band, which is situated in the spectral range 380–650 nm, in the presence of TiO2 NW. After increasing the TiO2 NW concentration in the TPU–TiO2 NW composite mass from 0 wt.% to 2 wt.% and 17 wt.%, respectively, a change in the binding angle of the TPU onto the TiO2 NW surface from 12.6° to 32° and 45.9°, respectively, took place.

The energy converted by a solar system is directly related to the amount of solar radiation falling on their surface. The tilt angle of solar panels is one of the most important parameter that affects the performance of the solar system. In the paper, an analytical model has been involved to determine the optimum tilt angle of solar panels, considering different time intervals for the readjustments of panel's slope. The main approach used in this paper to choose the tilt angle is to maximize the amount of global irradiation falling on the surface of the solar panels. Thus, based on a solar measurement database, the model has been applied to evaluate the optimum tilt angles of a photovoltaic system located in Iasi, Romania.

Proper planning of solar energy systems require accurate knowledge concerning the effective values of irradiation incident on solar system. One of the important parameters that provide information concerning the effective value of irradiation at the ground level is the clearness index, this index being directly related to the attenuation effect of the earth's atmosphere and the clouds. In this paper, a solar radiation database recorder in Iasi, Romania has been involved in a statistical analysis in order to evaluate the theoretical probability density function associated to the daily clearness index values.

The Terahertz’s wavelength is located between the microwave and the infrared region of the electromagnetic spectrum. Because it is non-ionizing and non-invasive, Terahertz (THz)-based detection represents a very attractive tool for repeated assessments, patient monitoring, and follow-up. Cancer acts as the second leading cause of death in many regions, and current predictions estimate a continuous increasing trend. Of all types of tumors, digestive cancers represent an important percentage and their incidence is expected to increase more rapidly than other tumor types due to unhealthy lifestyle habits. Because it can precisely differentiate between different types of molecules, depending on water content, the information obtained through THz-based scanning could have several uses in the management of cancer patients and, more importantly, in the early detection of different solid tumors. The purpose of this manuscript is to offer a comprehensive overview of current data available on THz-based detection for digestive cancers. It summarizes the characteristics of THz waves and their interaction with tissues and subsequently presents available THz-based technologies (THz spectroscopy, THz-tomography, and THZ-endoscope) and their potential for future clinical use. The third part of the review is focused on highlighting current in vitro and in vivo research progress in the field, for identifying specific digestive cancers known as oral, esophageal, gastric, colonic, hepatic, and pancreatic tumors.

The main topic consists of enhancing the geometrical and positioning accuracy of the machine tools with numerical control. Currently, in order to minimize the errors met during the vertical motions of the moving elements in the structure of a machine tool, various systems are used that are relatively complex and whose adjustments are difficult to do. This work is presenting a balancing–compensation system of the elements moving vertically that includes three invention patents; it has a simple structure that is easily adaptable to various types of machine tools. The newness element of the balancing-compensation system is represented by the pressure regulator being used, whose operation principle and design is described into detail. The related results have been reified in increasing by approximately 10 times the geometrical accuracy and, by default, the positioning accuracy of the element moving in a vertical plane.

This work presents a set of analytical design models to predict the electrical and mechanical properties of hybrid carbon nanotubes (CNT)/carbon-fibre (CF)/epoxy composites for potential use in fuselage and airframe constructions against lightning strike. The models are validated by experimental data from open literature. An optimization process is carried out to identify the microstructural configuration of the composite that provides the highest improvement in terms of electrical conductivity for the lowest structural weight in a CFRP fuselage design. The through-the-thickness conductivity of the composite laminate is considerably enhanced by a 2% volume fraction dispersion of CNTs within the matrix resin. The increase in the dielectric properties is accompanied by a moderate improvement of the composite mechanical performance. The hybrid CFRP/CNT composite configuration leads to a weight-efficient design solution for representative fuselage structures.

Electromagnetic compatibility issues and those generated by these radiations are a major concern for electrical and electronic products, mainly in the fields of communications, information technology, transportation, security and medical services. The paper presents the way to obtain nanostructured paint/plastic/nanopowder paint systems with electromagnetic shielding properties, as well as their characterization by FTIR analysis, DSC and dielectric tests. These systems have Electro-magnetic Interference (EMI)/Electromagnetic Compatibility (EMC) and Electrostatic Discharge (ESD) applications in the manufacture of enclosures for various electronic devices and for the automotive industry. At the laboratory level, 4 non-additive experimental models (EM) coded M1-M4 and 16 additive experimental models coded M5-M20 were obtained. Revolutionary to these materials is the fact that inside they are insulating and, on the outside, they behave like a shield. The results obtained from the dielectric tests performed on the 16 additive systems showed that the samples with a maximum percentage (20 %) of metal nanopowders show the highest values of electrical conductivity. Of the two nanopowders used, that of Fe from samples M11, M12, M19 and M20 which induces the composite higher conductivities than Al nanopowders. The ATR/FTIR spectra of the two paint samples analyzed showed that they were almost identical, suggesting that the paints tested had the same basic chemical structure. DSC analysis showed that pigment paint (V2) has low thermal oxidation stability and lower decomposition temperatures than pigment-free paint (V1), therefore, V2 is less stable under usage conditions, under the influence of normal environmental factors (temperature, humidity, natural or artificial light, etc.) compared to V1.