Browse Articles

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

The present study evaluates the marginal adaptation of fixed partial prosthesis made from resin composite. The main goal is to obtain restorations with excellent aesthetics and extremely high quality which increase the lifetime of the prosthesis system - dental structures. The method allowed the observation of defects that might occur during the technological processing, as well as their correction. It was used the 3D Shape software with which have been achieved scans for the virtual presentation the marginal adaptation. Following the investigation it was showed, that the cementation is extremely important, the errors occurring in this phase are influencing of the final results and behaviour. Composite resin fixed partial prosthesis are restorations which through a correct technology can compete with the ceramic fixed partial dentures. Keywords: aesthetic restoration, marginal adaptation, defects, 3D Shape software

In the last years, researches regarding the manufacture of polyamide parts using selective laser sintering process have developed increasingly more because of the advantages this materials offer. This paper was focused on a comparative study about the mechanical proprieties and surface roughness of parts manufactured by Selective Laser Sintering (SLS) from PA2200 powder. Tested parts were achieved on DTM Sinterstation 2000 Machine and EOS Formiga P 100 Machine. The results obtained lead to the conclusion that the mechanical proprieties obtained for the test parts made at 7,5W laser power on DTM Sinterstation 2000 Machine, are close to the results obtained for the test parts made at 30W on EOS Formiga P 100 Machine. Keywords: Polyamide, Selective Laser Sintered, mechanical proprieties, roughness

The concern for quality assurance and improvement of the manufacturing processes of plastic materials is of great interest to industry companies offering the guarantee to ensure the conformity, performance, competitiveness and profitability. This paper addresses the importance of improving the quality of plastics manufacturing processes, on high (flow) performance. It illustrates the application of the “Six Sigma” statistical method for injected products that have certain defects / nonconformities, especially dimensional manufacturing. Keywords: plastic products, quality, six sigma, manufacturing process, efficiency