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The J integral method was used to characterize the dependence of stresses and strains in the vicinity of the crack tip in thermoplastic materials with nonlinear deformations. This method makes it possible to establish the correlation between crack growth resistance of the material based on the stable propagation and the crack extension by means of J-R curve, which is an indicator related to the toughness of the material. The paper presents the results of experimental researches carried out on three-point bending test specimens of thermoplastic high density polyethylene - type PE 100, taken from the pipes with 110 mm diameter. Keywords: J-integral, J-R curve, toughness, thermoplastic materials, polyethylene PE 100

An incompressible MHD flow of two-dimensional upper-convected Maxwell fluid over a porous stretching plate with suction is studied. The nonlinear differential equation is solved approximately by means of the Optimal Homotopy Asymptotic Method (OHAM). Multiple solutions are given, showing a very good agreement between the analytical and numerical solutions. This procedure is very efficient in practice, ensuring a very rapid convergence of the solutions after only one iteration. Keywords: Maxwell fluid, porous stretching plate, optimal homotopy asymptotic method

One of the biggest dangers to our environment today is the increasing number of unused synthetic rubber in the environment and these pose a big threat to nature, if it is not disposed properly. Typically, synthetic rubber is developed for specific applications, and is specifically for those applications due to the process used to make them, and the resulting properties. Dumping these synthetic rubber in dumpsites could contaminate nearby water sources. Heating these synthetic rubber with normal heat will generate harmful chemical substances, like carbon and lead, which are really dangerous for humans. Dealing with rubber properly is not only advantageous to nature, but also to humans. Recycling represents a best alternative to the disposal of post-consumer rubber in common landfills if it is possible to obtain new materials with good final properties compatible with practical application. In this study, characterization and properties of virgin acrylonitrile butadiene rubber/recycle acrylonitrile butadiene rubber (vNBR/rNBR) were examined. Three different size ranges of rNBR particles, i.e., 150 - 350 mm, 2.0 -15.0 mm, and 5 -10 cm were used in this study. The vNBR/rNBR blends with blend ratios of 95/5, 85/15, 75/25, 65/35, and 50/50 phr (part per hundred rubber) were prepared using a two roll-mill at room temperature. The vNBR/rNBR blends with smallest size of rNBR particles show better tensile properties (tensile, elongation-at-break and M100) compared with all other blend ratios. For physical properties, vNBR/rNBR blends with smallest size of rNBR particles exhibited the highest hardness and cross-linking density at all blend ratios whereas resilience decreased, accordingly. The cross-linking density of vNBR/rNBR blends also show an increasing trend with increasing rNBR content. A morphological study of tensile fracture surface of the blends was also carried out. The scanning electron microscopy study indicates that rNBR exhibited a weak rNBR-vNBR matrix interaction particularly when more than 25 phr of rNBR was used, thus decreasing the mechanical properties of vNBR/rNBR blends. Keywords: vNBR, rNBR, Curing characteristic, Mechanical properties, Morphological properties

For determining the optimal conditions of the cutting process (material and tool geometry, process parameters), quantitative data are necessary concerning the roughness of surfaces. Using experimental research methods, this work aims at determining equations between surface roughness and parameters of the milling, process for some polyamides samples (PA66, PA66 – GF30 and PA66 MoS2). PA66, PA66 – GF30 and PA66 MoS2 polyamides are technical thermoplastics with excellent mechanical and physical properties, increasingly used in industrial machinery. Keywords: surface roughness, milling, polyamides

The maxillo-facial reconstructive surgery very often uses regular shape biocompatible material plates which are fastened by screws to the rest of the bone. The choice of optimal plate for each case, especially in risk cases, should be made primarily according to surgeon medical experience but also following a strength analysis of the various existing plates. The analysis of mechanical structures by using the finite element method highlights the resistance, the risky areas in case of possible demands such as the jaw’s pressure on the mandible, allowing the physician to optimize the restorative solution. Keywords: finite element, osteosynthesis

The choice of denture artificial teeth is made up onto several criteria regarding both aesthetics and functionality. Of these, colour stability is one of the determining factors. Colour stability of materials used in aesthetic prosthetic restoration is important for the long-term success of the treatment. Our study was conducted to compare colour stability of different acrylic artificial teeth available on the market and usually used in manufacturing partial and full dentures in Romania and to find a ranking of staining ability of different solutions with which artificial teeth could come into contact lately, during function or cleaning phases. For this study were purchased six boxes of identical front superior acrylic denture teeth from four different manufacturers, coded by letters V, M, R and S). These teeth were immersed in various liquids such as red wine, Coca Cola, black tea, coffee, which we considered to be ingested frequently by the largest part of the population. Our study shows that, of the four analyzed drinks, the most colouring is coffee. The same operator determined the color coordinates using the Easy-Shade intraoral spectrophotometer. The results were expressed using CIELAB colour notation system. Color difference was expressed as DE*. A device was made for constant positioning the tooth versus the Vita Easy Shade spectrophotometer rod used to determine colour changes in the central third of the buccal area. The acrylic prefabricated teeth suffered various colour changes in contact with those drinks, with magnitudes depending on the type of the liquid and the acrylic teeth chosen. We compared colour stability of two batches of homolog teeth, first unmodified and second grinded and polished in the dental laboratory, from which the most affected were R and M where this colour change occurs in three of the four kinds of drinks in which we have made the immersion. Washing the dentures with soap and water reduced differences in colour caused by contact with any type of these drinks. Keywords: color stability, denture, acrylic teeth, staining drink

Longevity of fixed partial dentures fiber-reinforced composite restorations is dependent upon many different factors, including material, maxillary or mandibular arches, patient- and dentist-related. 25 metal polymeric and 25 integral polymeric fixed partial prosthesis were obtained for this study. The Rx investigation was performed by using the Fona X 70. The possible defects were investigated with the DIAGNOcam using the transillumination method. In contrast to conventional technology with an interdental light source, DIAGNOcam practically uses the entire tooth as a light propagation medium. the transillumination investigation detects more defects trapped in the polymeric materials in 20 from the 25 metal ceramic fixed partial prosthesis and in 16 from the considered 25 integral polymeric fixed partial prosthesis. In conclusion, a noninvasive evaluations method, such as transillumination, has a great capability to evaluate the internal structure of the polymeric material used for the fixed partial prosthesis considered. Most of these defects were identified in the occlusal, cervical and connector’s areas of the fixed partial prosthesis and then could lead to fractures and failures of the prosthetic treatment. Keywords: polymeric fixed partial prosthesis, transillumination, non-invasive method, material defect

The paper focuses on the development of composite materials based on bacterial cellulose and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV). Natural composites were obtained from bacterial cellulose membranes and chloroform copolyester solutions (various mass ratios). The composite membranes were characterized by FT-IR spectroscopy, X-ray diffraction, SEM morphology, contact angle measurements and thermogravimetric analysis. Cellulose nanofibrils coating and/or precipitation with PHBHV particles was observed. The biocompatibility of composite materials was assessed by using L929 mouse fibroblast cells monolayers. Possible applications of these composite materials are focused on blood vessel engineering and/or wound dressing management. Keywords: bacterial cellulose, polyhydroxyalkanoates, composites, tissue engineering

Bimetallic Pd-Ag nanoparticles (NPs) were obtained by polyol method in the presence of poly (vinylpyrrolidone), PVP, as capping agent. The reduction of silver and palladium precursors was performed in argon inert atmosphere by successive reduction, or coreduction approach. In the successive reduction, AgNO3 solution was injected in the ethylene glycol solution of PVP at 140°C, followed by the injection of [Pd(NH3)4]Cl2 solution. The obtained bimetallic Pd-Ag NPs exhibited cluster structure, with the surface reach in silver. The NPs size was in the range of 30 – 58.5 nm with the average dimention of 41.5 nm. The coreduction approach consists in the hot injection of both metal precursors as complex ammine dissolved in ethylene glycol. By this method, smaller Pd-Ag NPs with the average sizes in the range 16 – 30 nm were obtained, depending on the synthesis parameters. The influence of metal cations : PVP molar ratio, metal cations concentration, Ag : Pd atomic ratio and the reduction temperature on the composition and morphology of the bimetallic NPs was studied. For both reduction approaches, based on the experimental data, two different reduction patways were proposed. Keywords: bimetallic nanoparticles, Ag, Pd, PVP, polyol method, coreduction, successive reduction

This study was focused on the synthesis of some new hybrid materials based on poly(amidoamine) dendrimer and halloysite designed for 5-Fluorouracil encapsulation. Different techniques like Spectroscopic methods (FTIR, XPS and UV-Vis) and thermogravimetric analysis were used to characterize the hybrid materials. The morphology of the hybrid materials was pointed out using Scanning Electron Microscopy ( SEM) analysis. The obtained results showed that the drug encapsulation efficiency of the hybrid materials was strongly influenced by the interactions between dendrimer-halloysite and drug molecules. Keywords: dendrimer, halloysite, 5-fluorouracil, UV-Vis, X-Ray Photoelectron Spectroscopy