This article aims to identify the behavior of light and heavy micro-plastics on the southern shore of the Caspian Sea during different seasons of the year. For this purpose, data from 15 sampling stations were gathered in four seasons, and subjected to various analyses after the samples were prepared. To separate light and heavy micro-plastics, the samples were washed with water. Analysis of TGA-DSC and FTIR imaging was used to quantitatively and qualitatively identify microplastic samples and optical microscope images were used to quantify the number of particles. According to the results, the amount of light microplastics in the spring and winter is less than in the summer and autumn. In the spring, the highest levels of pollutants are PVC, PES, PET and PU. In the summer and autumn, the values of PE, PP, PA, PAT, PU and PVC are at a relatively equal range. In the winter, most pollutants are PVC, PES, and PU. In conclusion, PE, PP, PPA, and PET should be removed from the environment before they can be modified by physical and chemical processes.
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A biomaterial must be biologically compatible, mechanical, functional, corrosion resistant and easily adapt to clinical and laboratory technologies. Dental biomaterials are materials used to replace a part of a living system or to work closely with living tissue. Many scientific articles present different polymeric biocomposites with possible application in dentistry and this is a proof of the opportunity of a research in a field in full ascent and with great availability in the promotion of materials destined to “work under biological constraint” and which must also meet the functional requirements of a dental implant. The objectives of this research were to obtain and to comparatively evaluate different polymeric microparticles that can be used in dentistry. The samples based on poly(lactic-co-glycolic acid) and respectively polyurethane microparticles were characterized by pH and Zetasizer measurements, and in vitro cytotoxicity assays. The results indicate the obtaining of particles with a neutral pH, medium homogeneity, and with different tendencies to form agglomerations. Their low cytotoxicity, tested on the primary human gingival fibroblasts by MTT and LDH techniques, indicates that these microparticles are safe to be tested in further clinical evaluations.
Polypropylene (PP) has a wide range of applications in the automobile bumpers due to its many excellent properties. Mechanical properties of PP for automobile bumpers are investigated through an artificial accelerated aging test. The aging rules after different years of normal use and the artificial accelerated aging test are analyzed. The correlation between natural and artificially accelerated aging is also explored. It provides a reference for the study of the aging properties of polymers for automotive applications. Results show that the UV aging test can effectively simulate changes in tensile and bending strengths after natural aging and can be used to evaluate the weathering resistance of PP materials used in automotive bumpers. The tensile and bending strengths of these materials remain good during aging, and elongation is sensitive to aging. The short-term artificial accelerated aging test does not exert a significant influence on the impact strength of materials, and artificial accelerated aging does not completely reproduce the aging process of the material.
Since the commercialization of Li-ion batteries by Sony in 1990, the performance of cathode materials used in Li-ion batteries has improved significantly. However, Li-ion batteries cannot respond to the needs of the energy storage market in terms of energy density. In order to increase theoretical energy density of active materials, molar mass of the active material should be decreased, or electron number participating per reaction or reaction potential should be increased. In this study, it was aimed to produce cathode materials for Li-ion batteries in the form of composite nanofibers via electrospinning method. For this purpose, porous LiFexMn1-xPO4/C composite nanofibers (1 > x > 0) were synthesized with a scalable, two-step method (electrospinning and subsequent heat treatment). The morphological, structural and electrochemical properties of the LiFexMn1-xPO4/C composite nanofibers were determined by scanning electron microscope, X-ray diffraction and galvanostatic charge/discharge tests. Cathodes made of LiFexMn1-xPO4/C composite nanofibers showed various advantages such as long cycle life, improved electrochemical performance etc. due to the presence of carbon and LiFexMn1-xPO4 in the composite structure. With the addition of Mn to the structure of LiFePO4/C composite nanofibers, electrochemical performance was improved. LiFe0.8Mn0.2PO4/C composite nanofibers showed the best performance in terms of energy density among the samples. Further increment in Mn/Fe ratio resulted declining electrochemical capacity and energy density.
The thermoset polymers and the thermoplastic polymers matrix composites require different forming techniques due to the different properties of two classes of polymers. While the forming technique for thermoset polymer matrix composites does not require the use of special equipment, the thermoplastic polymer matrix composites imposes the rigorous control of temperature and pressure values. Each type of polymer transfers to the composite a set of properties that may be required for a certain application. It is difficult to design a composite with commonly brittle thermoset polymer matrix showing properties of a viscoelastic thermoplastic polymer matrix composite. One solution may consist in mixing a thermoset and a thermoplastic polymer getting a polymer blend that can be used as matrix to form a composite. This study is about using PMMA solutions to obtain thermoset-thermoplastic blends and to mechanically characterize the obtained materials. Three well known organic solvents were used to obtain the PMMA solutions, based on a previous study concerning with the effect of solvents presence into the epoxy structure.
A significant part of the research and production activities is represented in the field of bioengineering by the biomaterials used in hard tissue restorations. They are of great interest in dental science, intending to improve technological aspects, monitoring their biological responses to the living organisms, but also to redesign economic aspects, beginning with the choice of raw materials. In the present work, light-curing composite biomaterials were made from a composite polymer matrix consisting of specific concentrations of bisphenol A-glycidyl methacrylate base monomer (Bis-GMA), a mixture of two co-monomers, triethylene glycol dimethacrylate and ethoxylated bisphenol A-dimethacrylate (TEGDMA/BisEMA), and two alumina nanopowder concentrations (5 wt.% and 10 wt.%). These materials were mechanically tested for flexural strength and compressive strength. The structural analysis of these materials consisted of SEM microscopy and EDX elementary mapping. In order to extract 3D projections of sample surfaces, but also to produce indicative values of their roughness, the SEM micrographs were processed with open-source software. In order to observe a clear evolution of the mentioned properties, the composite biomaterials were compared with materials formed only with the Bis-GMA/TEGDMA/BisEMA composite, and with a commercial composite resin, Filtek™ Supreme Ultra Universal Restorative, also. The findings showed an increase in the mechanical properties of the materials manufactured concerning the concentration of nanoparticles of aluminum. EDX analyzes confirmed the good homogeneity of nanoparticles in the polymer matrix. Mechanical properties of the manufactured nanocomposite biomaterials were reported 28.8 % higher than the control biomaterial. The comparison results with the commercial resin composite are encouraging.
Theobromine (Th) was documented during the last decades for its important role in the prevention of dental caries, having this role dueto its antibacterial action against the Streptococcus mutants and S. sanguinis, thus reducing the formation of dental biofilm on the teeth surface. Thermally induced interactions of theobromine in 1:1 mass ration bynary mixture with different types of Poly(methyl methacrylate) based materials and the induced interactions between Poly(methyl metha-crylate) based materials and HA were performed using thermal analysis and FTIR spectroscopy. This study aims to be a preliminary study for various mixtures of HA/methacrylate-based materials and Th with usage in dental applications. The instrumental techniques used can be successfully applied in the characterization of dental materials and can lead to conclusions on how to use them.Studies have led to the conclusion that Th can be used for the treatment of early decay by incorporation into the polymer material. It is recommended to use these materials as successive layers (Th with HA and after that dental material).
By the extrusion and injection technique, polymer-based composite samples (polypropylene and thermoplastic polyurethane) were obtained with BaTiO3 filler in concentrations between 0 and 35 %. Following the preliminary characterizations performed by coupled thermal analysis techniques, it was found that the composite samples obtained have thermal stability up to a temperature of about 250 oC and can be processed by extrusion at temperatures between 180 and 240oC. Above this temperature, a series of degradation processes take place by successive thermooxidation with the formation of volatile products.The electrical characterization of the composite samples was performed by the dielectric spectroscopy technique, which showed that the Ätgä dielectric losses increase as the BaTiO3 content of the composite increases. The maximum increase being recorded at 50 Hz (the slope Ätgä /% BaTiO3 about 0.003 /% BaTiO3). It was also found, that the electrical conductivity (ó) of the composite increases with the increase of content in BaTiO3 so that ó at 100 kHz for the composite with 35 % BaTiO3 is about 50 times higher than for the reference sample M 0 (without filler).
The present paper reported the obtaining of an environmental friendly adsorbent based on sodium alginate, chitosan and glass bubbles. CaCl2 was used as crosslinking agent for sodium alginate favoring the interactions by physical bonds between the negative groups (-COO) of biopolymer and the Ca ions. The experimental study to determine the Cu(II) uptake using an atomic absorption spectrometer was conducted in the testing stand at the 1:50 and 1:100 ratios between the adsorbent mass and the amount of pollutant in solution. The number of cycles of regeneration of the adsorbent material was also evaluated. The characterization of alginate/chitosan/glass bubbles adsorbent by scanning electron microscopy (SEM) coupled with energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FTIR) showed that the Cu(II) was found out on the surface of adsorbent.
Knowing how to deform the Turcite thermoplastic material under the action of conical penetrators is a means of obtaining information on the processing of the counterpart (made from a metal material with higher hardness) with which it comes into contact.The paper aims to theoretically determine the depth of penetration of the thermoplastic material under the action of some conical penetrators and to establish the coefficient of static and kinetic friction under the action of these penetrators. The proposed model will be validated experimentally on a tribological stand made for this purpose.