Volume 58, Issue 2

Abstract: 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.

Abstract: Polymer infiltrated ceramics are hybrid materials that combine the strength of ceramics and the flexibility of polymers. The aim of this study was to compare the fracture load capacity of monolithic CAD/CAM crowns with different occlusal thicknesses, made from polymer infiltrated ceramic network. Fifteen full contour CAD/CAM crowns made of Vita Enamic with occlusal thicknesses of 0.5 mm, 1.0 mm and 1.5 mm were fabricated with a wet milling machine. Restorations were cemented on human molars with adhesive cement. Samples were loaded along the long axis until fracture, with a single static compressive force. A scanning electron microscope (SEM) was used to examine the fracture surface of specimens after the fracture. The results of this study reveals that the fracture load of the samples increased progressively with the occlusal thickness. The highest fracture value was recorded for1.5 mm occlusal thickness of the crown. No statistically significant difference was reported between the three experimental groups. It can be concluded that hybrid monolithic CAD-CAM crowns showed sufficient fracture strength to be used for single restorations in the posterior area, even with a reduced occlusal thickness.

Abstract: The paper is part of a series in which the influence of the manufacturing defects on the functional behavior in biodegradation medium of some items obtained, both by 3D printing and by classical procedure (pressing), from an originaly renwable matrials based on polylatic acid will be presented. The first results regarding the correlation of the defects appeared at manufacturing into plates with the biodegradation behavior in an Aspergillus Niger(A.niger) medium, studied by SEM microscopy, are presented. These results demonstrated that the development of the A. Niger microorganism is related manly to the defects appeared at the melt processing of renewable polymeric material into finished product. A notable role in controlling the appearance of the manufacturing defects belongs both to the melt rheological properties which are responsible for the continuous or discontinuous flow and to the technical performance of the used equipement, 3D printer or classic hydraulic press. If the polymeric material melt has too high viscosity than the continuous flow is not possible and so the overlapped melt fronts are created which generate the voids formation, sometimes joined by small nano and/or micrometric channels. The rheological properties of the melts depend both on the material formulation and the seleted melt processing conditions.

Abstract: The widespread use of thermoplastic polymeric materials in various industrial fields has shown considerable interest in understanding the frictional and wear behavior. Among these polymers, polytetrafluoroethylene, also called PTFE, is a high-performance plastic that offers high chemical and thermal resistance and low friction. Additives such as fiberglass, carbon and graphite fillers are added to PTFE to significantly increase thermal conductivity, stiffness and self-lubricating properties. The materials subjected to the experimental analysis were pure PTFE, PTFE + 15% fiberglass, PTFE + carbon-graphite which slipped, under conditions of dry friction, on a sample of non-alloy steel construction SR EN 10025 from 1994. The tests were performed on a pin-on-disc tribometer. The effect of loading and sliding speed on the tribological properties of the polymer / steel combination under dry slip conditions was investigated and the specific wear rate for the experimental conditions was evaluated. The tests were performed at loads of the pin of Fn1=1N, Fn2=3N, Fn3=5N and Fn4=10N and sliding speeds of 1=1m/s, 2=3m/s. The results obtained indicated that the coefficient of friction decreases with increasing load. The wear rate for the analyzed materials was between 10-13...10-15 m2/N, the fiberglass reinforced PTFE material having the lowest wear rate. The present paper, through a comparative analysis of the friction and wear behavior, highlights the effects that the ingredients introduced in the basic material have, under the action of the exploitation factors (loading, sliding speed).

Abstract: Due to its chemical and mechanical properties, polyurea gains more and more interest in military applications. In this study, polyurea and carbon nanotubes were processed as coating polymer composites for ballistic plates and/or packages, in order to increase their protection potential, meanwhile maintaining an appropriate weight and an economic accessibility. In this respect, the composite material was layered on various commercially-available materials and various thicknesses and further, the performances of the products obtained were tested in order to assess their behavior against traumas produced by shockwave, blunt, shooting and fragment.

Abstract: This work is aimed at synthesizing an organic compound N, N`-bis(benzoyl) 1,3-cyclohexane-dicarboxylic acid dihydrazide (CABH) to focus on its effect on the non-isothermal crystallization of poly(L-lactide) (PLLA), meanwhile the melting behavior, thermal decomposition process and optical property of PLLA/CABH samples in different CABH concentrations were also investigated. It was found that CABH acted as efficient heterogeneous nucleating agent for inducing PLLA’s crystallization through comparative analysis of melt-crystallization process of the virgin PLLA with PLLA/CABH samples, and a high amount of CABH played a much more significant role in promoting PLLA’s crystallization. Additionally, the melt-crystallization processes also showed that both the cooling rate and the final melting temperature affected the crystallization behavior of PLLA, an increase of cooling rate could weaken the crystallization ability of PLLA/CABH samples, and the final melting temperature of 180°C made PLLA/CABH exhibit the best crystallization ability. For the cold-crystallization process, the cold-crystallization peak became flatter and shifted toward the lower temperature with increasing of CABH concentration, but an increase of heating rate could prevent the cold-crystallization peak from moving to low temperature because of the thermal inertia. The melting behaviors of PLLA/CABH depended on the previous crystallization and heating rate in heating, and the difference in melting behavior of PLLA/CABH samples effectively reflected the nucleation role of CABH, as well as the double melting peaks behavior of PLLA/CABH was thought to due to the melting-recrystallization. The introduction of CABH led to a drop in light transmittance, moreover, this negative effect were more obvious with an increase of CABH loading. In contrast, the fluidity of PLLA was significantly enhanced due to the existence of CABH.

Abstract: There is always time and energy optimization and reduction of faults the aim of research and in this context our article presents a study of a practical case of the deformation of a plastic part placed in a refrigerator for food storage, and that the use increases in number of these types of metals, are found in several sectors, and because of their industrial performance, a minimum residence time of the part in the mold is sought in order to reduce the cycle time of the process at the same time that the injection process is quite complex and requires a certain number of recurring questions to succeed. In the desired model. These are linked to residual stresses and deformations, pressure, mold temperature, filling threshold, shape of the part, but also to other mechanical and optical properties. Several investigations have been carried out and according to the authors the causes of these failures vary according to the manufacturing technique used. In this article, we try to find the origin of a deformation detected on a part at the end of the mold. Our work consists first of all in presenting, according to different studies, the thermomechanical properties of the material injected at different stages of the injection process. In a second step, compare the theoretical and analytical results. At the end of our study, we propose an optimization of the parameters necessary for the success of the molding and of the geometry of the assembly (mold and part).

Abstract: An additive is a substance, which when incorporated into polymer materials might lead at improvements on the electrical, thermal or mechanical properties of finished products in dependence of their applications, such as automotive, electronics, packaging and consumer goods. This study is based on the idea of using inorganic agents to change the basic properties of an epoxy resin. The well-known plasticizer 1-methyl-2-pyrrolidinone (NMP) was used to solve the inorganic agents and the mixture of obtained solutions was added, in certain amounts, into the epoxy resin prior the hardener of the epoxy system. The idea is to test the hypothesis of forming of ceramic nanostructures into the polymer structure based on local chemical interaction between solved inorganic compounds in certain conditions. The present paper concerns with the effect of changes on the mechanical properties of the epoxy resin.

Abstract: The aim of this work was to find the influence of the addition of low amount of hydrophilic and hydrophobic TiO2 nanoparticles on compressive strength, microhardness and rheological properties of flowable dental composite material. Specimens were prepared by adding 0.05; 0.2 and 1 wt. % of hydrophilic and hydrophobic 20 nm TiO2 nanoparticles. These specimens were compared to non-modified control specimens in compressive strength and microhardness. Furthermore, their rheological properties were determined. The optimal nanoparticle loading was 0.2 % hydrophobic TiO2, resulting in significantly higher compressive strength and microhardness than those of the control specimen group. Mechanical properties of flowable composites reinforced with hydrophilic and hydrophobic TiO2 at higher loadings are lower than those of control specimens, which is the result of nanoparticle agglomeration. TiO2 nanoparticles addition resulted in the decrease in viscosity in all specimens except for the specimewn with 1% hydrophilic TiO2 nanoparticles. In accordance to the obtained results, hydrophobic nanoparticle addition results in a more resistant and durable material, combined with an increased flowability compared to a non-modified composite.

Abstract: Although polymethylmethacrylate (PMMA) is widely used as a denture base material, its disadvantages include low strength and low thermal conductivity. The effects on thermal conductivity, flexural strength, thermal diffusivity, and elastic modulus of adding Al2O3 and SiC powders in different volumes to PMMA were investigated. A total of 60 specimens were prepared in 10 groups (five groups for the thermal conductivity test and five groups for the flexural strength test (n:6). The specimens were immersed in water for 30 days before the testing. Thermal conductivity values were measured by the transient hot bridge (THB) method, and flexural strengths were measured by the 3-point bend test. A significant difference was found in thermal conductivity, flexural strength, thermal diffusivity and elastic modulus values between independent groups (P < 0.001) using the Kruskal-Wallis test. The Kruskal Wallis 1-way ANOVA was used for the post hoc tests after Kruskal Wallis (á=.05). The thermal conductivity of PMMA increased significantly with the addition of 15% SiC and 15% Al2O3. The flexural strength values decreased significantly with the addition of 10% SiC and 15% Al2O3. The thermal diffusivity values increased significantly with the addition of 10% and 15% SiC. The Young modulus of PMMA decreased when 10% SiC, 10% Al2O3 and 15% Al2O3 were added. Environmental scanning electron microscope (ESEM) showed that ceramic powders were dissipated in PMMA. The addition of 15% SiC powders to PMMA increased thermal conductivity without significantly reducing flexural strength. This study helped determine the optimum volumes for the use of SiC and Al2O3 powders. Knowledge of the importance of this variable will help in more effective modification of denture base resin with SiC and Al2O3 powders to improve heat transfer without adversely affecting strength.

Abstract: Renewability, recyclability and biodegradable contents are similar to glass fibers in natural fiber reinforced polymer composites (NFRP) which have definite mechanical properties. The interface of polymer matrix and natural fibers results the composites to achieve superior properties of products. Researchers have extended their product designs and production techniques by using renewable materials such as jute fiber, cotton fiber, silk fiber, etc. which are enormous and used in the manufacture of durable industrial goods of high-end quality. This paper reviews the current developments and the brief findings needed in literature, concentrating on the mechanical properties and applications of NFRP.

Abstract: In esthetic restorative dentistry, resin composites are generally encountered. Because of their excellent biocompatibility, lack of taste, odour, tissue discomfort, and toxicity, insolubility in body fluids, ease of use, good clinical/ aesthetic properties, stable colours, optical characteristics, efficient pigmentation, low cost, and repairability, they are becoming more common. Currently used composite resins have some flaws, particularly inconsistent mechanical properties. For a long time, particles of various sizes have been used as fillers to enhance these properties. In prosthodontics, poly(methyl methacrylate) (PMMA) is commonly used as a dental base material. It does, nevertheless, have several weaknesses, including low strength and weak thermal properties. The effects of different sizes of alumina (Al2O3) particles on the poly(methyl ethacrylate) (PMMA) denture base were determined in this experiment. PMMA powder was blended with Al2O3 added to methyl methacrylate (MMA).For PMMA polymeric materials strengthened with Al2O3 (40 nm, 140 nm and 0.3-0.8 μm) in various concentrations, the mechanical properties were studied.Also, the synergetic influence of the three nanoparticle sizes in the resin matrix was studied.Furthermore, thermogravimetric (TGA) analysis and water absorption and solubility characteristics of the composites prepared were also examined. Among the most significant properties to be obtained for good denture materials is high mechanic properties, water absorption and solubility, since they have different attributes in the aqueous condition of the oral cavity. Results showed clear properties optimization, especially for the size-hybrid alumina composites.

Abstract: Abstract: The presented experimental research aims to compare the degradation degree of five different types of surgical sutures used in clinical practice and to discuss the influence of local pH on the degradation of a suture material. The surgical sutures were tested in terms of stability and hydrolytic biodegradation in Phosphate Buffer Saline (PBS) solution varying the pH and the immersion time of the samples in the liquid medium. The surface properties, structural characteristics and the effects of hydrolytic biodegradation on the mechanical properties were studied using Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Degradation degree and Tensile Strength tests, respectively.

Abstract: The article presents the optimization of a production process with the help of FDM technology of a fertigation pump prototype that does not require other energy source than that given by the flow and pressure of water for irrigation. In the research presented in this article specimens of PETG material are tested in terms of mechanical properties by using a tensile test equipment. The results of these tests are used to dimension and simulate with finite element the component elements of the pump.

Abstract: Previous studies have shown that marine drug propylene glycol alginate sodium sulfate (PSS) plays important roles in human diseases. This study mainly explored the effects of PSS on hyperglycemia and hyperlipidemia in diabetic db/db mouse models. The db/db mice were randomly divided into 5 groups (n=12), which were model control group (distilled water), positive control group (metformin), PSS low, medium, and high dose groups (PSS25, PSS50, PSS100) and normal control group (C57/BL, distilled water). The mice in each group had free diet and water for 90 days. During the experiment, food intake was recorded every day and body weight was recorded weekly. In addition, fasting blood glucose and glycosylated hemoglobin levels were measured regularly. Finally, the contents of triglyceride (TG), low-density lipoprotein (LDL-c), high-density lipoprotein (HDL-c) and total cholesterol (TC) in the serum of mice were determined. PSS can significantly reduce fasting blood glucose and glycosylated hemoglobin levels in db/db mice, and improve insulin sensitivity. Moreover, PSS can reduce the fat accumulation of db/db mice and significantly improve the blood lipid level of db/db mice. PSS can significantly improve the symptoms of glucose and lipid metabolism disorders in db/db mice.

Abstract: An original functionalization strategy is proposed here to design chitosan (CS)-based cryogels with ethylenediaminetetraacetic acid (EDTA) moieties. Cryogels with aligned micro-sized tubular structures were further engineered through an unidirectional freezing approach. Attachment of EDTA groups onto CS chains was proved by 1H-RMN and FT-IR spectroscopy. The formation of EDTA-functionalized 3D porous CS-based cryogels was demonstrated by several methods of characterization (FTIR spectroscopy, optical microscopy, SEM, porosity measurements, swelling behavior, copper (II) retention capacity). The sorption tests pointed out the high potential of EDTA-functionalized CS-based cryogels for heavy metal ions retention.

Abstract: The purpose of this research is to study and develop the formulation of a rheological law for composite materials with elasto-plastic behaviour in cold compression. Starting from the generally known relationships in literature, the hypoelastic model proposed for the composite materials behaviour (as powder materials) has been developped/explained, ensuring the understanding of the research. The hypolastic theory has been used for modeling the continuous transition from elastic to plastic state for a powder material. The material behaviour is described through an isotropic tensor relationship between the deformation speed tensor, Cauchy’s stress tensor and its derivative in relation to time (the Jaumann’s derivative). Only the linear part has been used from the general form of the law which depends on scalar functions. The calculations lead to relationships depending on five parameters which are identified according to experimental data. A numerical simulation of the stress-strain evolution during the simple compression of a diepressed powder sample is made; the numerical simulation has been validated by the experimental results.

Abstract: The paper presents the study on the static mechanical properties of PLA (Polylactic Acid) produced with entry-level additive technologies using three printing directions. During the experimental work were tested a total of 15 “dog bone” ASTM D638-14 standard specimens made from additively manufactured polymer (PLA) through FDM (Fused Deposition Modelling) technique, where the material and rectilinear pattern infill geometry and infill percentage of 100% were constant and the printing orientation was varied. Usually technical data sheets that are delivered by filament materials producers include the most satisfactory data which are valid for only one specific printing direction. The printing direction is deliberately selected, in such way that the best material characteristics are achieved. In addition to this matter, as the additive manufacturing market grew significantly in the past couple of years, the filament production market showed a consequential growth. The aftermath of this expansion had a direct impact towards the quality and costs of the filaments used for 3D printing, in order to satisfy both the low-end and high-end users. Therefore, in this frame, the present research provides entry-level additively manufactured PLA performances showing significant changes depending on the different printing directions and determine the build orientation influence on the mechanical properties, in the aim of providing aid for both mechanical designer and product manufacturer at the stage of the printed product mechanical properties.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.