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Fiber reinforced composites (FRC) are used in periodontal therapy for stabilization of mobile teeth with compromised bone support. The type of fiber and the type of composite have a great influence on mechanical properties of FRC. The specimens made of different FRC systems were subject to a three-point bending test. The results indicate that the specimens which exerted the best ratio between high deflection, low flexural modulus and medium flexural strength have the best indications to be used in periodontal therapy. Regarding the fracture pattern, the FRC recommended for splinting are those that separate in two discrete parts while maintaining an intact polyethylene fiber. This aspect allows intraoral repairs, increasing the life-span of the periodontal splints. Keyword: fiber reinforced composite, periodontal splint, three-point bending test

The purpose of this study is to assess the effects of artificial saliva with different pH on the wearing of glass ionomer cements. We used three types of glass ionomer cements and three immersion environments. We have prepared a total of 96 samples. We used 6 artificial saliva samples for each environment. Each sample was immersed in the storage solution to a specific pH. Storage solution was changed on days 1, 7, 14 and 28. Glass ionomer cements are influenced by the storage media, showing significant changes in the case of an acidic environment (in our case, artificial saliva with different pH). As long as the material is tolerated and protected by the tooth structure, resistance to abrasion will be satisfactory. Keywords: glass ionomer cements, pH, artificial saliva, wearing

A number of inventions, and theoretical and experimental research allowed to increase the thermal homogenous melt flow-rate delivered by the screw. On the other hand, quality of the extruded product depends on geometrical considerations of the extrusion head and on a large scale on the rheological behaviour (viscous and elastic) of the polymer melt. Non-harmonizing the design of the screw-barrel unit with the construction of the extrusion head can lead to low-quality products. In this paper, the extrusion head working field was drawn based on limitations imposed by the screw-barrel unit, i.e.: maximum flow-rate assuring required melt thermal homogeneity; - maximum flow-rate for which the heating system on the barrel (and screw, eventually) assures the extrusion temperature; -minimum flow-rate corresponding to screw diameter. Keywords: extruder head working field, extruder performance, rheological behaviour, screw-barrel unit

The spectral shifts in the visible electronic absorption spectra of B3 in water-ethanol mixtures were correlated with the macroscopic parameters (refractive index and electric permittivity) of the solvents. The contributions of the intermolecular interactions upon the spectral shifts as a function of the solvent macroscopic parameters were expressed by multiparameter regressions. The dependence of the wave number in maximum vibronic band of B3 vitamin on the solvent macroscopic parameters demonstrates the prelevance of the orientation interactions in the studied solutions. Some electro-optical parameters and global descriptors of B3 vitamin were computed by Spartan program. In present, the assimilation of the B3 vitamin copolymeric compounds in medicine and cosmetics must fullfil the complexity of the biological issues that result from using them. We note that the B3 vitamin can be incorporated in the polymeric structures to improve its functions. Keywords: solvents effects, absorption spectra, B3 vitamin

Protonation, quaternization and addition reactions of poly(N-vinylimidazole) to the imidazole nitrogen atom in the position 3 to obtain the corresponding ionic derivatives were studied by NMR Spectroscopy. Information and data about the reaction type and product microstructure are presented. The chain tacticity is a special structure aspect which was in detail studied by means of proton and carbon NMR spectra confirming that the chain configuration is not modified by any of the three polymer-analogous reactions. Keywords: poly(N-vinylimidazole); polyelectrolytes; benzyl chloride; trifluoroacetic acid; acrylic acid; chain tacticity; polymer microstructure

This paper, intended to continue the previous work under the same title, published in the previous number – aims at presenting the experimental results, obtained by laboratory tests, referring to the influence of the massic percentage of the hemp hurds within the composites, as well as to the influence of the participation percentages of the filling materials (cement, lime, sand, plaster etc.), on the thermal-transfer factor. The experimental results place thereby this composite in a position comparable to other construction materials; which emphasizes the importance of this composite, with a view to its being used as construction material, both as boards (for lining) and as blocks (for filling). The analysis of the experimental results shows that this type of composite can be ”programmed” and ”controlled” in terms of thermal-transfer factor, through the massic participation percentage of the hemp hurds. In this way, one can extend the use of these composites over constructions in areas with variable temperature differences, especially in the cold season. Moreover, by these experimental values, one can devise a methodology for sizing the construction elements, based on thermal-transfer factor to be achieved and, implicitly, on the thermal insulation capacity to be provided by the respective construction. Keywords: composite, hemp hurds, thermal-transfer factor

This paper presents an analysis of a composite cell at a micro level. The authors modeled the interface between a micro sphere and a polymeric matrix for two cases: an interface characterized by a strong bond between the two involved bodies and an interface with low friction between the micro sphere and the polymeric matrix. Even if these models are ideal images of actual composites, the analysis of strain and stress distributions reveals there is a big difference in the mechanical behaviour of the two micro cells. These two cases were analyzed considering a perfect elastic behaviour of involved materials. The shape and the intensity of stress distributions are different for the analyzed models. A weak interface makes the matrix to have restrained zones with high values of von Mises stresses, concentrated on top and bottom of the sphere (on the loading direction). An actual cell of a similar composite (polymeric matrix and a micro sphere as reinforcement) could not have an „extremist” behaviour as these two here presented, but an intermediate one, depending on actual properties of the materials and the nature of the interface. Keywords: micro cell composite, strain distribution, stress distribution

In this paper we studied the dyeing behaviour of polyester fibers from recycled polyester and virgin dyed with Foron brilliant rot SGL (CI Disperse Red 121). The amount of dye fixed recycled fiber is higher than that of virgin. Elemental analysis confirms a slight change in the carbon and oxygen content of recycled fiber compared to virgin. Thus the recycled polyester fiber carbon content is higher than virgin fiber in oxygen exchange is less. Dyed samples were treated with AgNO3 in order to confer antibacterial properties. The analyses SEM/EDAX have highlighted the presence of silver ions on the surface of fibers. Keywords: dyeing, recycled PET, virgin PET, disperse dye, antimicrobian effect

In this paper the buckling problem is solved for the laminated composite structures from a thin-walled metallic cylindrical shell which is strengthened by fiber-reinforced polymers. The research concerning the influence of composite thickness and fiber orientation on axial critical buckling load is executed. For linear buckling problem, the purposed method is based on modified relations for an orthotropic cylinder. The method was verified by comparison with buckling theories of laminated composite shells and with numerical results based on finite element method. Keywords: lamina/ply, buckling, analytical modelling, numerical analysis

This paper analyses the influence of processing temperatures of polyamide 6.6 Grivory type HTV-3H1 noir 9205, polyamide 6.6 Grivory type HTV-45H1 noir 9205 and polyamide 6.6 Grivory type HTV-6H1 noir 9205 on some mechanical properties, when injecting items used in various technical articles. The test-specimens on PA 6.6 Grivory type HTV-3H1 noir 9205 were molded at the following injection temperatures: 310, 320, 330, 340 and 350°C. The test-specimens on PA 6.6 Grivory type HTV-45H1 noir 9205 were molded at the following injection temperatures: 320, 330, 340, 350 and 360°C. The test-specimens on PA 6.6 Grivory type HTV-6H1 noir 9205 were molded at the following injection temperatures: 330, 340, 350, 360 and 370°C. These specimens were tested using methods for determination of the following mechanical properties: tensile strength, Izod impact strength and hardness (Shore). For all these polymers, it was determined that increasing of injection temperature results in insignificant changes of hardness. The Izod impact strength decreases with increasing the injection temperature. After reaching the minimum value, Izod impact strength increases again if the processing temperature is raised further. The tensile strength at break increases with increasing the processing temperature. After reaching the maximum value, tensile strength at break decreases if the processing temperature is raised further. Keywords: polyamide 6.6 (PA 6.6), tensile tests, Izod impact test, Shore Durometer hardness test