Browse Articles

Numerous studies have shown that the geometry of the femur and pelvis affects the distribution of the occurring tensions and movements. The study was performed on the 3D model (three dimensional), of the coxofemoral joint which was achieved through CT images (tomography computer). The results confirmed that the values of tensions and displacements slightly differ from those in the literature due to the geometry and the properties of the used material. Keywords: finite element analysis, hip joint, mechanical properties, modelling

Conducting polymer coating has been used to improve the surface performance of metallic materials, as Ti6Al7Nb alloy. Polypyrrole (PPy) was electrochemically deposited from 0,2 M oxalic acid aqueous monomer solutions by three different methods: potentiostatic, galvanostatic and potentiodynamic techniques. The stability of PPy / Ti-6Al-7Nb surface has been studied by electrochemical methods in Hank’s Balanced Salt Solution (HBSS) by Tafel tests and cycle voltammetry. The PPy / Ti-6Al-7Nb biofluid interface was analysed by electrochemical impedance spectroscopy (EIS) and the corresponding equivalent circuits were proposed. The structural infrared analysis and morphology of conducting polymer layer on titanium alloy have been evaluated. Keywords: Polypyrrole, Ti6Al7Nb alloy, stability properties, EIS, AFM

Epoxy-based composites with modified carbon nanotubes (CNTs) were synthesized using different types of CNTs. These were first modified by amidation of the carboxylic groups from the CNT’s surface and then embedded into the epoxy matrix. The modified CNTs and the corresponding composites were analyzed by FTIR, TGA, DMA and Raman Spectroscopy. The influences of CNT type and the nature of the organic modifier were pointed out in connection with the composites structure. Keywords: functionalization, carbon nanotubes, polymer nanocomposites, thermostability, Raman Spectroscopy

A number of four polymer conditioned fertilizers, with slow release of active compounds, were synthesized and characterized. The new fertilizers have been obtained in solid form, through a crosslinking impregnation method. The influence of pH, temperature and molar ratio between raw materials on the activity index was investigated in order to reach an optimization of the process. The products were investigated using modern techniques, as Fourier transform infrared microscopy, HPLC, 1H-RMN or scanning electron microscopy. Keywords: slow release, fertilizers, polymers, conditioning

Polymer complexation is one of the convenient routes for the development of new polymeric materials. Polymeric complex based on poly(aspartic acid) and poly(ethylene glycol) is an interesting compound due to its attractive properties brought by the both components. Poly(aspartic acid) belongs to the family of synthetic polypeptides and it is a biocompatible and biodegradable water-soluble polymer, and owing in part to the carboxylic groups has some similar chemical properties to that of poly(acrylic acid). Poly(ethylene glycol) is also an interesting nonionic polymer because it is soluble in water and several organic solvents, due to the presence of both hydrophobic and hydrophilic segments. The near-infrared chemical imaging (NIR-CI) method is the fusion between near-infrared spectroscopy and image analysis with the unique capability to provide both qualitative and quantitative data of localized and space-averaged chemical compositions. The NIR-CI technique is successfully used in pharmaceutical applications to reveal the extent of ingredient blending, particle size distribution, the presence of polymorphs, and trace contaminants. In the present study the homogeneity of the polymeric complex based on poly(aspartic acid) and poly(ethylene glycol) it was evaluated, using NIR-CI technique which was also sustained by zeta potential and FT-IR analyses, the methods being employed in order to characterize the compound as future potential biomaterial structure. Keywords: biomaterial, poly(aspartic acid), poly(ethylene glycol), NIR-CI

The structure of dielectric materials is one of the main important parameter, which determines the durability of products. The degradation process runs differently in various types of polyethylene, because the macromolecules present different level of branching, different crystallinity grades, different chemical resistance. The dissimilarities between the resistance on ageing of different sorts of polyethylene are depicted by FTIR analysis, chemiluminescence determinations and the measurement on electrical resistivity. The consequences on the long term service under g-irradiation degradation are discussed. Keywords: polyethylene materials, degradation, FTIR, chemiluminescence, electrical properties

The amphiphilic polymers can form associated structures in aqueous solution by mutual interaction and/or interaction with other components such as surfactants and active colloidal molecules. In this paper, results regarding nanolevel associative behaviour of chitosan based systems with surfactant and paracetamol are presented. The viscosity measurements of the solutions prepared were made with a view to take into consideration viscosity as an associative parameter. The thin films topography obtained by spin-coating was analyzed by Atomic Force Microscopy (AFM). The nanostructured matrices were investigated by Scanning Electronic Microscopy (SEM), X-Ray Diffraction (XRD) and by Fourier Transform InfraRed (FTIR) Spectroscopy. From FTIR and X-Ray investigations it can be concluded that, at nano - level, in the chitosan matrix, crystalline surfactant and paracetamol domains like nanocapsules are localized. By visual analysis of the AFM and SEM images it can be observed that the nanocapsules are orderly structured in horizontal layers and present a vertical gradient, the paracetamol nanocapsules formed having dimensions in the range of 21 – 170 nm. The chitosan-paracetamol nanostructured matrices obtained by the phase inversion method stand as a remarkable candidate to be used to control release of this drug. Keywords: chitosan, paracetamol, cationic surfactant, structural analysis

The paper presents the corotating twin screw extruder optimization, taking into account the quality of final product. Thus it was established the optimum screws configuration, the optimum screw speeds and the optimum flow rates. Keywords: twin screw extruder, quality, flow rate, screw

A new aromatic diamine, namely 2,2-bis(3-amino-4-oxyhexyloxy-phenyl-4’-butoxyazobenzen) hexafluoropropane, containing two azobenzene side groups have been prepared by modification of 2,2-bis(3-amino-4-hydroxyphenyl) –hexafluoropropane with 4-(6-bromohexyloxy)-4’-butoxyazobenzene in the presence of K2CO3/KI. This monomer showed a mesophase in the range of 103-114°C and can be used for obtaining of polymers with special optical properties. Keywords: butoxyaniline, side azobenzene groups, thermal characterization

Knowing that copolymers of acrylonitrile (AN) with acrylic acid (AA) can be used for the molecular imprinting, three AN: AA copolymers were synthesized by radical copolymerization in emulsion without emulsifier. The copolymer and diosgenin were dissolved in dimethylformamide (DMF) in order to obtain casting solutions with various polymer and template concentrations. The influence of the copolymer and template on the rheological behavior of the solutions was studied in order to establish the best parameters for the casting solutions preparation. The polymer solutions were transformed in membranes by phase inversion in water at room temperature (20oC). By casting the polymer solutions on a glass surface and drawing down with a scraper, a 200 mm thickness film resulted. The diosgenin was extracted from the membrane structure with ethanol, methanol or chloroform in an ultrasonic bath. The molecular imprinting was proved by HPLC on liquid (the extracting solvent after the membrane extraction) and solid phases (after dissolution of membrane parts in DMF). Comparing the sorption capacities of the imprinted materials, for two steroids (diosgenin and stigmasterol), the membrane selectivity towards the template was proved. Keywords: imprinted polymer, molecular recognition, solid phase extraction, bioactive substances,phase inversion