Browse Articles

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

Water soluble cadmium selenide (CdSe) nanoparticles were chemically obtained by polymer assisted synthesis at 70 Celsius degree from aqueous solution, using Cd(CH3COO)2·2H2O or Cd(NO3)2·4H2O as cadmium source and H2SeO3 as selenium source. The clustering of CdSe nanoparticles synthesized in poly(amidehydroxyurethane) matrix was clearly revealed by X-ray diffraction and Atomic Force Microscopy films studies. The obtained CdSe nanocrystallites have hexagonal symmetry with an average dimension of 25 nm. The Fourier Transform Infrared spectra show the interaction between the nanoparticles and urethane carbonyl and C – O – C etheric groups of polymer. The dimension of CdSe – polymer entities in water solution was explored by Laser Diffraction method and confirmed the capping of CdSe nanoparticles by the polymer. Keywords: CdSe, nanoparticles, polymer assisted synthesis, structural characterization

The flow rate coefficient was calculated both theoretically, based on calculus relationships, and experimentally, based on data obtained on two extruders with screw diameters of 45 mm and 90 mm, respectively. The concordance of the theoretical results with those obtained experimentally in two situations were verified, namely: free discharge, no backpressure, and discharge with backpressure. Keywords: flow rate coefficient; feeding zone; single screw extruder; flow rate

Due to their lightweight, exceptionally high strength and modulus, high stiffness, good fatigue life, and excellent corrosion resistance, polymer matrix composites are increasingly being used in the aircraft and spacecraft industry. Nowadays, a significant amount of advanced polymer composites is used for military and commercial aircraft and satellite components. Due of their low density, higher physical and mechanical properties and low manufacturing cost, these materials have replaced metals, such as aluminum alloys, in many applications. This paper deals with the class of polymer composites, new material recipes and testing results. This approach refers to the possible use of ferrite additive to improve mechanical and magnetic properties of polymer composites. Keywords: lightweight, polymer, composite, ferrite

Construction of passive insulation elements in neoprene single microstructure mixture has demonstrated that the isolators can have the necessary elastic characteristics but low internal damping. The reduced scale models have in the structure viscoelastic materials basing on natural rubber symmetrically distributed in respect to the geometrical reference system chosen for the isolator. The materials consisting of natural or synthetic rubber are used as filling elements symmetrically located so that, globally, the isolator can be properly characterized both at compression and shear. For the present paper there were used two material types modelled as Voigt-Kelvin and Hooke-Maxwell elements. Key words: rheological modelling, antivibrating isolator, composite neoprene

Pralidoxime chloride (PAM) was encapsulated in biopolymeric membranes in order to evaluate the kinetics of release in aqueous solution. PAM is an efficient cholinesterase reactivator with a pronounced hydrophilic character. The biopolymeric membranes were prepared by crosslinking, directly in aqueous solution and the monodisperse spherical microcapsules made by this method had diameters between 1 and 3 mm. PAM was embedded “in situ” in microcapsules prepared from natural polymers as sodium alginate, chitosan and gelatin. The release data were fitted by first order kinetic equation, Weibull, Peppas and Higuchi semiempirical equations to obtain the kinetic parameters of controlled PAM release. The embedding of PAM in biopolymeric membranes was achieved in order to prepare a sustained release pharmaceutical formulation for oral administration. Keywords: biopolymeric microcapsules, Pralidoxime chloride, drug release

The most modern restorative interventions in dental practice are mainly based on a new generation of composite materials specialy designed for this kind of applications. Their complex structures offer a quasi-plastic behavior concerning the special tribological phenomenon developed in the intraoral environment. Starting from this, the paper intends to present the experimental data obtained as research results for two composite materials - InLine (IVOCLAR) and HeraCeram (HERAEUS Kulzer). The study is focused on the influence of the most important mechanical factors from occlusion areas such as loads, lubricants, speeds, composite materials hardness concerning the wear processses and their influence onto the mastication areas. Keywords: composite materials, tribology, wear, dental medicine