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Copolymers based on dicyclopentadiene and maleic anhydride have been reacted with several aromatic amines (typical polymer-analogous reaction) to obtain the corresponding amides, and subsequently imides. An appropriate procedure has been established and the conversion has been appreciated. All the products have been characterized from the structural point of view, as well as by measuring the improved thermal properties. Keywords: dicyclopentadiene; maleic anhydride; polymer-analogous reaction; thermal properties

New reinforcing agents based on modified montmorillonite with different amines and polyhedral oligomeric silsesquioxanes were synthesized and characterized by different techniques like FTIR Spectrometry, Thermogravimetric Analysis (TGA), X-Ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). DSC analyses show that the presence of the modified montmorillonite leads to an increase of epoxy resin reactivity due to the catalytic effect of the montmorillonite modifier which included amino groups. The glass transition temperature (Tg) for the final hybrid systems which contain modified montmorillonite with amines exhibits lower value than the epoxy systems without any reinforcing agent. The thermostability of the final hybrid systems was not influenced by the introduction of these reinforcing agents. Keywords: epoxy, layered silicate, polyhedral oligomeric silsesquioxanes, glass transition temperature, nanocomposites

New polymeric nanocomposites based on nanostructured reinforcing agents as Polyhedral Oligomeric Silsesquioxanes (POSS) with methacrylic groups were synthesized and the influence of POSS type was studied. As polymer matrix a mixture of functionalized POSS and triethylene glycol dimethacrylate (TEGDMA) was used by replacing the classical diglycidyl methacrylate monomer (BisGMA) with various POSS functionalized with methacrylic groups. The obtained nanocomposites were characterized by spectroscopic methods (FT-IR, RAMAN), thermal analysis (TGA, DMA) and scanning electron microscopy (SEM). Keywords: polyhedral oligomeric silsesquioxanes, nanocomposite, thermostability, FT-IR, RAMAN, TGA, DMA, SEM

The aim of this study is to investigate the interaction between pure collagen and mineral phases like hydroxyapatite. For that purpose, collagen fibers were mineralized starting from hydroxyapatite aqueous precursors. The mineral phase identification was made by XRD, the collagen-hydroxyapatite interaction was studied by IR spectroscopy, the microstructure of the composite materials was investigated by SEM and the amount of mineral phases’ deposition was evaluated by ATD-TG. Ultrasonication was used in order to evaluate the strength of the collagen-hydroxyapatite bond. The obtained results showed that it was obtained a collagen – hydroxyapatite composite material, characterized by a strong interaction between the collagen fibers and the hydroxyapatite crystals, which can be successfully used as a bone substitute. Keywords: collagen fibres mineralization, hydroxyapatite, electrostatic interactions

The dynamics of the plasma discharge through spontaneous symmetry breaking as double layer Langmuir, anodic patterns etc., is treated by means of the fractal description. Considering that the charge carrier movements take place on fractal curves, the electric charge transport is studied in an extended model of scale relativity. Using the motion equation for the complex speed field for the irrotational movement the generalized Schrödinger equation is obtained, and in the absence of dissipation a generalized Korteweg de Vries type equation is obtained. The process is also analyzed at the microscopic scale, when the electrical conductance increase is controlled by means of the soliton coherence. When the external field exceeds a critical value, the solitons which stocks the energy break down and simultaneously release the energy to the environment. The same mechanism can explain the charge transport in composite materials (e. d. nanostructures). Moreover, some correspondences between the theoretical model and the behaviour of the patterns generated by laser ablation are analyzed. Keywords: fractal space-time, charge transport mechanism, nanostructures, composite materials

This work presents a theoretical model of calculation of cylindrical assemblies joined with adhesive, based on an energy method. After the determination of the cinematically acceptable field of stresses, according to the applied load, a variational calculus on the expression of elastic potential energy leads to the complete expression of the stress field in the whole assembly. A first parametric analysis (geometrical and physical parameters) is carried out on an assembly of tubes and makes it possible to deduce the optimal length and the thickness of the adhesive. The model is validated by comparison with a finite elements model. For the assembly, the total force-displacement behavior is well defined. Thus the analytical model makes it possible to determine the rigidity of the assembly and to obtain a simple formulation very rapidly which gives the total behavior of the assembly. Keywords: adhesive joints; glass fibers; modeling; finite element analysis, stress transfer

This paper contains the results of an experimental study regarding the thermal stability of the urethane and alophanate groups from model compounds obtained in chemical reactions between phenylisocyanate and mono- or bifunctional stabilizers. The results can be used to estimate the thermal stability of the polyurethanes which were thermal and photo-oxidative (additive and reactive) stabilized. Keywords: urethane, alophanate, phenylisocyanate, antioxidant compound, photo-stabilizer compound

The aim of this study was to optimize microwave post-polymerization treatment parameters, power and irradiation time, in order to achieve the maximum applicable flexural and impact strength of autopolimerizing poly(methyl-methacrylate) denture reline resins. Specimens were produced from two types of commercial materials. Control group was left untreated, while the other twelve were post-irradiated in a microwave oven with different power and time settings: 500, 550, 600 and 650 W; and 3, 4 and 5 minutes. The amount of residual monomer was determined using DSC and FTIR. Furthermore, visual control has been conducted, in order to check if there any surface changes have appeared. Microwave post-irradiation resulted in increase of all tested mechanical properties, for all specimens. The highest mechanical properties were obtained with maximum irradiation power, which was confirmed by the results of ANOVA statistical analysis. It has been found that residual monomer content strongly influences the benefits in all tested mechanical properties, increasing biocompatibility. The fracture mode of all specimens in untreated and treated conditions was found to be mostly brittle. However, the highest power (650 W) and the longest irradiation time (5 min) resulted in unacceptable surface color and roughness modifications. Keywords: biopolymers, microwave post – polymerization, mechancal properties, residual monomer

Orthopedic research in hip endoprosthesis is advancing rapidly. The new techniques that are being used in the domain of Rapid Prototyping (RP) have given the possibility to build scaffold structures from metallic and plastic materials. This paper presents the designing process and a FEM simulation of a tailored hip endoprosthesis with a scaffold structure which is placed all over the stem and also brings into discussion the fixation place, which is influenced by the in-growth process of the bone tissue. The hip endoprosthesis simulation use as material Ti6Al4V because it is biocompatible and can be used to manufacture the endoprosthesis using RP technology like Electron Beam Melting (EBM). Keywords: scaffold structures, orthopedic implants, electron beam melting, modeling

The paper presents the use of FEM (Finite Element Method) for calculus performing at the injection moulding of a high accuracy part made of plastic material type Polyacetal, referring at: pumping of the mould cavity, thermal resistance and mechanical strength. There are presented: diagrams of variation for the pumping full degree function of time at four temperatures of the mould, thermal representation of the part for the temperature of the mould at 80oC, the results obtained after the part’s testing at drop-test, the results of static stress for the part made of injected plastic material. Keywords: injection moulding, pumping, thermal resistance, mechanical strength