Browse Articles

News on Green Energy and Green Hydrogen is spread on popular and academic media. When energy is obtained from sunlight, wind or water, we call it Green Energy. When hydrogen is obtained from electrolysis with Green Energy, we call it Green Hydrogen. Hydrogen Fuel Cells are electrochemical devices that convert hydrogen and oxygen`s chemical energy into electricity and heat energy with high efficiency and contribute to the decarbonisation of the power supply. Bipolar plates, essential components of the fuel cells, made in polymer-carbon composites, are an economical alternative to the stainless steel, titan and graphite, traditional materials. Our experiments have used a polypropylene matrix filled with graphite with a total inorganic content of 87%, which contributes to high electrical and thermic conductivity but strongly influences the viscosity, flow, pressures, temperatures, and then challenging to process. Injection Moulding of thermoplastics is a technology widespread in all fields of activities and considerable potential. In this paper, the experiments` design is highlighted in choosing the factors. A debate regarding the filling, packing, holding pressures, and the last decades` approach and optimisation of injection moulding parameters with the Taguchi Method is presented. Conclusions on the injection moulding process of the bipolar plate made of a polypropylene-graphite composite, the parameters` influence with direct effects on the fuel stack`s performance are presented. The combined melt and mould temperatures influence most electrical conductivity by better contacting the electrically conductive particles through the polymer`s melted layer. The injection pressure influences the mass and thickness of the product and the electrical conductivity by better packing. Furthermore, we suggest an adapted formula to predict the injection pressure considering the inorganic content and the process temperatures in agreement with the experiments.

In this study, the properties of unsaturated polyester resin were studied in the presence of recycled ceramic waste particles. Herein, composites were created that contained 28.5-50 wt% porcelain particles (particle size [180 µm). High filler contents increased the gel time and decreased the exotherm temperature of unsaturated polyester resin during curing. The obtained results showed that physical parameters, such as the resin density and porosity, increased as the filler content increased. In addition, the X-ray diffraction results indicated that the produced samples were a combination of ceramic waste particles and unsaturated polyester resin, resulting in semi crystalline structure. The results showed that the maximum water absorption at 40°C increased from 0.97 to 1.5% as the filler content increased from 28.5 to 50 wt%; in this process, the materials experienced a color change but did not lose mechanical performance. Finally, the samples were characterized by thermogravimetric analysis (TGA) to study the effect of porcelain powder on the thermal degradation of the resin. The TGA scans were analyzed with the Friedman method. The results indicated that the samples with porcelain powder exhibited substantially better thermal stability than unsaturated polyester resin.

Samples of LDPE (low-density polyethylene) and LDPE-PANSA (low-density polyethylene -4-Amino-3-hydroxy- 1-naphthalenesulfonic acid) copolymer with Ag0.5·Ni0.5·Fe2O4 powder (as a filler) composites were developed. Following the preliminary characterizations on the thermooxidability (by thermal analysis techniques), the dielectric behavior (by dielectric spectroscopy technique), the mechanical behavior, etc. it was found that the developed materials do not show significant changes after 240 h exposure to 150 mW / m2 UV. The addition of 3wt% PANSA in LDPE has the effect of increasing the mechanical performance of polymer composites with Ag0.5·Ni0.5·Fe2O4 filler. The addition of 15 wt% ferritic powder leads to significant increases in dielectric losses (by about 100% in the case of pure LDPE and about 185% of the LDPE copolymer with 3 wt% PANSA) and to the increase of the real component of the relative permittivity (by about 34.4 % in LPDE, respectively about 36.4% in LPDE copolymer / 3% wt PANSA). Dielectric behavior of the investigated materials indicates that the effect of Ag0.5·Ni0.5·Fe2O4 powder in LDPE and of copolimer LDPE with 3 wt% PANSA consists in the increasing of the shielding efficiency of electromagnetic waves - the maximum effect being recorded in the case of the composite material with the content: LDPE 84.5 wt%, 2.5 wt% / PANSA and 13% wt% Ag0.5·Ni0.5·Fe2O4.

Initially developed as a rapid prototyping tool for project visualization and validation, the recent development of additive manufacturing (AM) technologies has led to the transition from rapid prototyping to rapid manufacturing. As a consequence, increased attention has to be paid to the mechanical, chemical and physical properties of the printed materials. In mechanical engineering, the widespread use of AM technologies requires the optimization of process parameters and material properties in order to obtain components with high, repeatable and time-stable mechanical properties. One of the main problems in this regard is the anisotropic behavior of components made by additive manufacturing, determined by the type of material, the 3D printing technology, the process parameters and the position of the components in the printing space. In this paper the influence of the printing orientation angle on the tensile behavior of specimens made by material jetting is investigated. The aim was to determine if the positioning of components at different angles relative to the X-axis of the printer (and implicitly in relation to the multijet printing head) contributes to anisotropic behavior. The material used was a photopolymer with a mechanical strength between 40 MPa and 55 MPa, according to the producer. Four sets of tensile test specimens were manufactured, using flat build orientation and positioned on the printing table at angles of 0˚, 30˚, 60˚ and 90˚ to the X-axis of the printer. Comparative analysis of the mechanical behavior was carried out by tensile tests and microscopic investigations of the tensile test specimens fracture surfaces.

Graphene, a two-dimensional crystalline allotrope of carbon, has received greater attention from numerous researchers due to its excellent properties. Graphene could be produced by various techniques, each method has its advantages and disadvantages. In this research article, a novel method using agricultural waste rice husk as a precursor and chemical activation to produce few-layer graphene nanosheets was developed. Traditional approaches` significant shortcomings and the environmental concern of agricultural waste have been eliminated. The synthesized material was characterized using FESEM, Raman Spectroscopy, X-Ray diffractometer, UV-Vis absorbance and FTIR analysis. FESEM analysis of the surface morphology revealed smooth edge few-layer graphene. The formation of sp2 hybridized atoms can be seen in XRD spectra at 26.3 degrees. The C=C stretching bonds detected at 1612 cm-1 wavelength are responsible for the graphitic structure.

Some inventions along with theoretical and experimental research made it possible to increase the output of a thermally homogeneous melt provided by the screw. However, the quality of the extruded product depends on some specific features of the extrusion die and to a large extent on the rheological behavior (viscous and elastic) of the polymer melt. The mismatch between the design of the screw-cylinder subassembly and the design of the extrusion die results in products with relatively short service life. The present paper has drawn up the working field of the extruder die and adjusted it based on the limitations imposed by the screw-cylinder subassembly, namely: - the maximum output rate that ensures the required thermal homogeneity of the melt; - the maximum output at which the heating system on the barrel (and possibly the screw) ensures the extrusion temperature; - the minimum economic output corresponding to the diameter of the screw. The working field of some extrusion dies for blown films of the following polymers have been plotted: polypropylene, low density polyethylene, high density polyethylene and ethylene vinyl acetate.

The number of surgical procedures for abdominal wall defects is increasing, often requiring the insertion of plastic material meshes. Surveillance of patients with inserted plastic meshes requires an accurate determination of the position of the mesh. However, this is a difficult task, depending on the kind of mesh, magnetic resonance imaging (MRI) protocol or consistence of the surrounding tissue (fat, muscle, aponeurosis). The aim of our research was to develop an experimental model to test the ability of MRI to identify the exact position of surgical plastic meshes: polypropylene or polyester. To simulate the placement of a mesh in human body we developed a model built up from two pieces of tissue with dimensions of 40 cm x 20 cm, harvested from a pig with a weight of 120 kg. The meshes were situated for MRI evaluation between the two pieces: abdominal pig muscle respectively suprajacent abdominal pig wall subcutaneous fat, approximately 2 cm high. Five surgical meshes were scanned through six MRI sequences, in view of establishing an optimal MRI scanning protocol and best visible meshes. The MRI scans were evaluated by 5 radiologists with different degrees of training. Our results showed that the experimental model developed by us can be successfully used to test the ability of MRI to visualize different kind of plastic meshes. Also, our experiment has revealed that T1fl2D sequence is the best in highlighting meshes from surrounding tissue, and the best visualized Mesh was number 4, made of polyester. In conclusion, based on our experimental model, we should select a plastic mesh or MRI protocol which will allow an optimal post implantation monitoring. Modern technology of material’s fabrication can help to better identify the mesh itself using MRI scanning.

This study determined and compared the influences of various processing techniques including air circulating oven (ACO), dry heat oven (DHO) and water bath (WB) on the impact strength (IS) and microhardness (HV) of the conventional heat cure acrylic resin (CHCAR) and rubber reinforced heat cure acrylic resin (RRHCAR). Samples were fabricated using CHCAR (control Group A; n=114) and RRHCAR (experimental Group B; n=114). Group A and B were further divided into subgroups according to processing techniques: ACO, DHO and WB (n=38 each) for both testing variables microhardness and impact strength (n=19 each). Charpy testing machine and Vickers microhardness tester were utilized. Analysis of variance was applied to determine the presence of significant differences among processing techniques while P-value ≤ 0.05 was considered as significant. Water bath (P-value [0.001) and DHO technique (p-value [0.001) showed significant differences between both groups’ impact strength and microhardness. Microhardness of group A and B showed a significant difference (p-value 0.002) when processed by ACO. Impact strength and micro hardness were improved in RRHCAR compared to CHCAR processed by ACO and DHO in comparison to WB technique. Rubber reinforced heat cure acrylic resin revealed improvement in the impact strength and microhardness. The air circulating oven exhibited highest microhardness in both testing materials. Dry heat oven showed improved values of impact strength in conventional heat cure acrylic resin.

Mechanical characterization of newly developed polymers and composites are the basic measurements that are used to check the potential of the material towards its usage in various applications. Young researchers who are new to the field of materials science often find it difficult in selecting the specific testing standards for their novel materials. This review article provides a detailed explanatory of the various ASTM standards that are used for analyzing the basic mechanical properties of polymer composite materials. The standard dimensions of the test specimens and the mechanical testing parameters that are universally followed in different testing phases are illustrated for the ease of research.

The purpose of this study was to investigate changes of superficial topography and wettability of two injection-type denture base materials following low pressure plasma treatment. Samples of denture base materials (Polyan and Biodentaplast) were fabricate using dedicated technology and were exposed to plasma treatment. Resin surface topography and rugosity were evaluated using SEM and AFM, while wettability was determined through contact angle measurements. Artificial saliva was the testing liquid. Initial contact angles for the two materials are close (Biodentaplast-37.60°, Polyan-36.75°). Plasma treatment halves the values of the contact angle. 30-days measurement reveals a reduced bounce-back effect (Biodentaplast-20.68°, Polyan-20.11°). Surface topography modified differently for the two materials. Rugosity increased significantly for both materials (p[0.05). Surface rugosity values pre- and post-plasma treatment respect the biological threshold of fungal adhesion. Plasma exposure increased injection-type denture base materials wettability with artificial saliva and surface roughness. Injection-type denture base materials and artificial saliva can enhance prosthetic experience of xerostomic patients.