Volume 59, Issue 1

Abstract: Despite important progress in the field of the thin flexible transistor (TFT)-based electronics, a major challenge still exist for organic TFTs to decrease the operating voltage, which is related to the properties of the dielectric and semiconductor layers from the OTFTs structure. In this paper, we present the electrical behavior of two biocompatible polymers, polyvinylpyrrolidone (PVP 360) and polyvinyl alcohol (PVA), regarding the application as insulating layer in thin-film transistors. The PVA and PVP 360 thin films were deposited onto epoxy resin copper double-sided layer and polyethylene tere-phthalate/Indium tin oxide (PET/ITO) substrates by sol-gel method, spin-coating technique. Two sol concentrations (1 and 5 wt. %) were prepared and the contact angle onto the used substrates was measured using a digital microscope camera. The obtained films have been characterized by scanning electron microscopy (SEM) and dielectrical behaviour. For electrical measurements, the metal-insulating-metal (MIM) structure was realized by cooper electrodes deposition at room temperature, onto the top of thin films, by magnetron sputtering method. The current (I) - applied voltage (from -5 to +5 V) curves were measured in air at room temperature (RT), using the Picoammeter homemade device. PVA and PVP 360 thin films showed low leakage currents with values within ± 2 nA for ±5 V range.

Abstract: The aim of this work is to study the possibility of using the products of aminolytic destruction of polyethylene terephthalate (PET) and their derivatives in polymer composite materials with vibration-absorbing properties, which provide effective damping of vibrations of technogenic and natural origin in a wide temperature and frequency range. The paper considers a modern method of recycling PET waste with a mixture of amino alcohols - monoethanolamine and triethanolamine, taken in two different ratios. As a result of the destruction reaction, terephthalic acid diamide (N, N`-bis (2-hydroxyethyl) terephthalamide) is formed. To accelerate the destruction process, microwave radiation of various powers of 200, 540 and 700 watts was used. The optimal conditions for aminolytic decomposition of PET were determined: the time and power of microwave radiation with PET conversion up to 95% and the yield of the target product (terephthalic acid diamide) 80-85%. The destruction process was carried out according to a closed cycle of using reagents, without the use of catalysts and at atmospheric pressure, which to a certain extent reduces the energy consumption and increases the environmental friendliness of this method of PET decomposition. The aminolytic degradation product of PET (terephthalic acid diamide) was used as a monomer in the polycondensation reaction to obtain a new oligomer (terephthalic acid oligoesteramide). The degree of polymerisation (n) is in this case 7 to 11 (number of chain links). The obtained oligomer and the PET degradation product were investigated as new components in elastomeric compositions based on chloroprene rubber and in compositions based on thermoplastic elastomers. It has been demonstrated that the introduction of an oligomer based on a PET degradation product reduces the viscosity of elastomeric compositions by 25-35%. The study was supported by a grant from the Russian Science Foundation No. 21-79-00301, https://rscf.ru/project/21-79-00301/.

Abstract: The substantial increase in the use of the FDM (Fused Deposition Modeling) process for the production of plastic parts in ever wider fields has led to the search for methods to improve the quality of the printed parts. In the case of ABS parts (Acrylonitrile Butadiene Styrene), one of the most common and used methods to improve surface quality is the process of acetone steam treatment, but the application of this method also brings more or less negative effects on the part. The main side effects when applying this method is the low breaking strength and loss of part details on the sharp edges. This paper presents a set of contributions on the relationship between surface quality and the level of detail of parts subjected to acetone steam treatment. In order to analyze the influence of the treatment on the details of the parts, a reverse engineering method was used in which a polyarticular arm FARO Edge 7.5 was used to scan the parts and reconstruct them. The study was performed on parts with 20% infill, grid tipe.

Abstract: With the fourth industrial revolution, Additive Manufacturing started to offer new possibilities of manufacturing, Fused Deposition Modeling being one of the most used processes for fabrication. In this paper, the studied specimens are manufactured based on the Fused Deposition Modeling (FDM) method, with a filament of short carbon fiber and polyethylene terephthalate (PET) matrix, with a variation of the layer thickness. For the resulted specimens the tensile properties are determined according to ASTM D638. The most advantageous results are obtained for the layer thickness of 0.15 mm, with the tensile strength of 58 MPa. Based on the stress-strain curves which are presented in this paper, it also can be assumed that the material is brittle. The results of the mechanical properties are very similar for each group of specimens and it can be assumed that the mechanical properties are homogenous due to the material quality and the machine performances. For all the specimens the rupture location is almost in the same area. Due to the difficulty of carbon fiber filament printing, the manufacturing defectives which appear during the manufacturing process are detected, the most common manufacturing defectives being the material gaps from each specimen, which are identified with microstructural analysis. As failure modes, the most common failure criteria are the delamination and the matrix cracks.

Abstract: An innovative recycling process for thermoset composite laminates is proposed by thermo-mechanical disassembly and further compression molding of hybrid thermoformable composite plates. Due to the thermo-mechanical process, single cured plies are extracted from the waste laminate. Subsequently re-lamination is performed by interposing thermoplastic films between the reclaimed composite plies. Final consolidation is carried out by compression molding. In order to show the feasibility of the novel recycling technology, carbon fiber reinforced composite plates by autoclave molding were thermo-mechanically disassembled in a manual roll bending machine after heating in oven. Reclaimed cured plies were laminated by alternating thermoplastic interlayers made of low density polyethylene. The hybrid laminate was consolidated at the temperature of 220°C and the holding pressure of 38.5 bar. Results from bending tests on virgin and recycled plates showed the very good agglomeration of the hybrid samples and the optimal preservation of performances of initial cured plies of the virgin material into the recycled plate.

Abstract: Results on mechanical properties of Tensylon® composites at room temperature are presented. Single-ply and two-ply samples, obtained from the ply-precursor sheet (of two orthogonal layers) have been subjected to: load till failure in traction, at different strain rates (below 10-1 s-1) and cycles of successive loading and unloading and 5 min stress relaxation period. The characteristic times of relaxation are evaluated and the difference in values of Young modulus before and after the relaxation stage is established. A complex cyclic/relaxation test requires a visco-elasto-plastic model of Tensylon®, and allows to quantify it. This model predicts the material behavior in other types of tests: for instance, it predicts strain rate independence of loading to failure in the considered strain rate range. Cyclic tests fulfilled at a fixed strain rate suggest that Tensylon® is an elastoplastic material without noticeable viscosity. The proposed model, additively including nonlinear viscoelasticity and plastic flow with strengthening, shows a satisfactory agreement with experimental data. It also agrees that the material is strain-rate-insensitive in the range 10-3 s-1–10-1 s-1.

Abstract: Several phenylazophenoxyacetic acid derivatives were obtained starting from azophenols and ethyl chloroacetate by an environmentally friendly approach. The synthesis reaction was carried out in heterogeneous medium using P(AAm-co-DADMAC) copolymer. Good results have been obtained thanks to phase transfer catalysis. Retrosynthetic and structural analysis were performed.

Abstract: In the recent past, the demand for multifunctional and lightweight materials have increased steadily creating an increase in demand for Hybrid polymer matrix composite which consists multiple fibers in conventional resins. In this study, a hybrid composite comprising of two reinforcements - natural silk fiber and E-Glass fiber - in an Epoxy resin matrix which is a partially eco-friendly composite has been fabricated and the effect of drilling, by using an 8 facet solid carbide drill, on the surface roughness has been studied. Taguchi’s L27 Orthogonal array was used for experimentation by modifying three parameters - feed rate, spindle speed and drill diameter - on three levels (low, medium and high) and thereby studying the effects. From the results of experimentation it has been observed that increase in spindle speed and drill diameter reduces surface roughness however it increases with increase in feed rate. Further, regression analysis and Fuzzy modeling are used in order to determine optimum parameter values to get the desired surface finish. Good agreement between the experimental, regression and fuzzy model is observed with the correlation coefficient of 0.9814 and 0.9677 respectively.

Abstract: At the beginning of the 90`s on the market of dental restoration materials appeared compomers, polyacid modified composite resins (PMC). The term compomer suggests a combination of glass-ionomer and composite technology. This has led to confusion about how it relates to dental structures. The properties and adhesion of compomers to dental structures suggest a closer connection with composites than with glass ionomers. They do not have direct chemical adhesion to any tooth structure it adheres similar to the composites through a separate binding agent. However, their proximity to composites does not make them substitutes of composites. Compomers are a versatile class of dental restorative biomaterials, whose clinical benefits are particularly useful in pediatric dentistry.

Abstract: Infections that occur after the insertion of biomedical devices are a major problem; potential sources of infection are due to the adhesion of bacteria on the surface of implants, bacteria that form biofilms. In order to combat or to effectively prevent various microbial, which occur in medical procedures, we try to make compounds and materials that prevent the formation or development of microbial biofilm. The aim of this study was to obtain nanostructured surfaces based on magnetite, carboxymethylcellulose and ceftriaxone, as films with anti-infective properties in order to use them in the field of current biomedicine. To obtain nanostructured surfaces with high non-stick potential, the carboxymethylcellulose-functionalized magnetite powder was homogenized with an anti-infective agent, ceftriaxone. From the analysis of the obtained results it was found that the nanostructured surfaces obtained had a strong antimicrobial character infections and can be used successfully in the coating of medical implants, in order to combat the microbial biofilm.

Abstract: The objective of this study is to demonstrate how the effect of adding multi-walled carbon nanotubes (MWCNTs) nanoparticles to the (Hydroxyapatite /High-density polyethylene) bio-composites. In this investigation, the samples with various percentages of (MWCNTs) were fabricated by a hot-press technique. The morphological characteristics, roughness of the surface and thermal properties of the bio-composite samples (HA/HDPE/MWCNTs) were investigated. The excellent homo-geneous distribution of the internal fibrous network and microstructure arrangements were among the most prominent characteristics obtained through FE-SEM and AFM examinations. The degree of crystallinity showed that the (MWCNTs) additives enhance by an increase of approximately (35%), compared with pure sample (without addition MWCNTs). Based on the experimental results obtained, the fabrication of the presented bio-composites sample exhibited the excellent characteristics that make them promising material for biomedical application as a substitute material for hard tissue likes bone reconstruction.

Abstract: In this work an attempt had been made to hybridise the Epoxy resin by incorporating the Pterocarpus Marsupium natural resin powder derived from the Pterocarpus Marsupium tree. The mechanical, dynamic mechanical, biodegradability and thermal stability of the blended polymer was evaluated at different Pterocarpus Marsupium resin particulate loading (10, 15, 20, 25, 30 and 35 v/v %). The composite specimens were fabricated by using hand layup method. The mechanical properties such as tensile strength, flexural strength had shown significant improvement than the tensile modulus and flexural modulus due to blending, the experimental results indicated that the better properties of the blended polymer were obtained at 30% v/v Pterocarpus Marsupium resin incorporated Epoxy polymer. Soil burial test revealed that the incorporation of bio resin resulted in weight loss of the blended polymer over prolonged period of time.

Abstract: The paper addresses the methodology for obtaining biocomposite structures from waste, with sound-absorbing properties, such as: thuja shells, walnut shells, pistachio shells, beech sawdust, pumpkin seeds shells and sunflower seeds shells. The experimental analysis carried out considers the study of the sound-absorbing properties held by the proposed new biocomposite materials, by determining the value of the sound absorption coefficient, reflection coefficient, impedance ratio, using the Kundt tube. The interpretation of the results obtained from the evaluation of biocomposites shows that they have sound-absorbing properties. Consequently, sound-absorbing panels with soundproofing properties can be made from these materials, which can be used in industry, transportation, construction, etc. as well as for decorative purposes in spaces such as cinemas, malls, spas, etc.

Abstract: Compomers have emerged by modifying dental composites in an effort to combine their desired properties, namely their good aesthetics, with those of glass ionomer cements, namely their ability to release fluoride for a long time. While this combination of good aesthetics and fluoride release may seem to give compomers an advantage, their poor mechanical properties limit their use. The main components of the compomers are polymerizable dimethacrylate resins, such as urethane dimetha-crylate and TCB (a butantetracarboxylic acid reaction product) and hydroxyethyl methacrylate and ionizable glass fillers, such as fluorosilicate glass.

Abstract: Otitis and middle ear disease present high morbidity rates in spite of current medical treatment, especially in the younger population. Otitis media with effusion (OME) is a chronic disease that is often found in school age children. Its evolution, recurrence, complications and resolution still present a challenge to otologists. For some time, middle ear ventilation tubes were used for this pathology, thus assuring proper middle ear ventilation and higher disease resolution rates. In the current paper, we investigate the connection between ventilation tube usage, the materials out of which they are made, the techniques involved and how these factors may influence disease resolution rates.

Abstract: In the recent years, the number of patients treated with fixed orthodontic appliances is permanently increasing, as well as their interest for esthetic treatment issues. One potential unwanted consequence of orthodontic therapy is the onset of white spot lesions on teeth enamel during treatment. The present review includes studies published between 2010 and 2021 on three different databases (Science Direct, PubMed, Google Scholar) regarding the implications of nanoparticles in white spots prevention. The initial databases search identified 471 entries. Following the PRISMA-P 2015 guide, 39 scientific articles were selected for full text evaluation. The studies were divided into four categories. The interpretation of studies included in this review permits us to sustain the idea that the use of nanoparticles in various orthodontic materials improves their bioactivity, decreases the biofilm appearance around components of the fixed appliances, and can even initiate remineralization in the enamel proximity. Most of the analysed articles are in-vitro studies of new biomaterials properties, in the recent years depicting an increase interest of the researchers towards randomized control trials regarding clinical use of new orthodontic biomaterials.

Abstract: In construction building, the optimum insulation material thickness determines the efficiency of energy consumption. In this paper, heat transfer and the temperature distribution of recycled polymers between construction building components are investigated using theoretical and simulation methods. It has been shown that when the thickness of all recycled polymers being studied is increased, insulation improves and energy consumption decreases, indicating that XPS is the best recycled plastic and the optimum thickness is 7 cm. In this work, experimental and numerical approaches have been used, to conduct a qualitative and quantitative analysis of the thermal performance of an external wall outfitted with new insulation materials, based on the most commercialized recycled thermoplastic polymers (Polyethylene RPE, Polyethylene terephthalate RPET, and Expanded Polystyrene RXPS) waste.

Abstract: In this study is presented the result obtained for the treatment of waste water from the medical sector using membrane filtration system. Polyethersulfone (PES) membranes were obtained using Dimethylformamide DMF like solvent, with different concentration to determine the rejection variation of different dyes. Membranes were obtained by the immersion precipitation method and permeation properties were determined by dead end technique. The results show that the membranes filtration method can by improved to reduce the cost of the water treatment from the medical sector. Using DMF solvent membranes with a smaller concentration of polymer have a good rejection results in comparison with other membranes obtained with different solvents.

Abstract: Composites that have a good to lower weight ratio can be used to replace conventionally used Engineering Materials. The properties of natural fibers are almost equal to that of artificial fibres. Natural fibers can be used in many applications and is also a cost-effective material. Bagasse fibre reinforced with dry palm kernel fibre powder is used to improve mechanical properties and fabricated in plate form. In this research work, the input constraints that have been used to fabricate the plate are 10, 20, 30 wt% of bagasse fibre, 10, 20, 30 wt% of palm kernel fibre, at 10, 15, 20 MPa compression pressure and 2, 4, 6 mm of speciemn thickness respectively. The optimization has been performed by Taguchi L27 orthogonal array and influence of output parameters viz. Tensile Strength (MPa), Flexural Strength (MPa) and Hardness (Hv) have been measured by using statistical analysis of variance. The multi-criteria decision making of the output parameters has been performed by Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). This research offers new insight into decision-making, particularly in the optimization part, to increase the strength and mechanical property of natural fiber composites.

Abstract: This in vitro study aimed to compare the fracture resistance between pressed custom-made polyetheretherketone (PEEK) post and core and fibre reinforced post and composite core. A total of 40 single rooted extracted teeth were selected, endodontically treated, and prepared to receive the posts. Specimens were randomly divided into two main groups (n=20/group): group 1, (PEEK); group 2, fibre post. PEEK post was manufactured with a computer-aided design/computer-aided manufacturing system further divided into four sub groups (P7, P12, F7, F12) based on lengths 7 and 12 mm at which the posts were cemented. All posts were cemented with self-adhesive resin cement, and specimens were stored in 0.1% thymol solution during the experiment at all the times except during preparation and testing. A universal testing machine was used to measure the fracture resistance. The fracture resistance values (mean & SD, in newtons) were 1255N (P7), 1562N (P12), 1065N (F7), and 1384N (F12). Only P12 exhibited a significant difference (p,0.05). The turkey test showed an association between failure mode and post and- core material. In the remaining groups, most failures were nonrepairable and related to fracture. Customized post-and-cores of PEEK exhibited good mechanical performance. Their fracture resistance was comparable to that observed for fibre posts.

Abstract: The high heels footwear industry is permantly evolving due to the increasing attention given to combine confort and elegance. The purpose of footwear has changed with the evolution in the fashion industry and it is no longer limited only to protect the feet. This paper represents a first step to develop customized shoes outer sole, taking into consideration the unicity of each individual anatomy. Another important aspect is the manufacturing of these outer soles using plastic materials. The additive manufacturing presents itself as a viable option in obtaing a working prototype. Based on previous research, an analysis has been performed in order to optimise the design and its functionality. The study validation has been done using FEA and Topology Opimisation.

Abstract: Generally, the importance of bending test has been employed to analyse the induction level of internal resistance of its larger face size of the test speciemens. Comparatively, stress induction is quite larger at the perpendicular face, where the bending load has been initiated its point of contact. Therefore the estimation of the location of maximum stress induction on bending test specimen must be analysed for the purpose to estimate the breaking point of test specimen, which supported a lot in the lifespan estimation of a component. In this work, three different composites are selected under the category of primary composites and thereby underwent the bending testing for the purpose of material refinement to tackle compressive load based applications. Three-Point flexural tests are conducted on the primary composites. The internal molecules bonds at peak loads are visulaized through SEM approach. Thus, the perfect inital and boundary conditions for computational strurtual analyses are found out. Ansys Workbench is an advancement tool, which is used in this work for composite generation and structural simulations. All the computational tests are effectively executed with the help of advanced coupling facility between different working environments. Finally, the numerical results are compared with experimental results and then suitable material is shortlsted based on high load withstand capacity. Additionally, the conventional analytical approaches are used to validate the flexural outcomes. Further, the advanced finite element analyses are expanded to advanced composites materials such as nanocomposites, shape memory alloys based composites, and sandwich composites. From the above all studies, the superior material is finalized based on the outcomes of this multi-inclusive investigations.