Volume 46, Issue 4

Abstract: The railways mounting must ensure by strength and stability of the components, the guiding safety and running quality of the railways vehicles at the prescribes speeds and loads. The upper structure of the railroad is made from the ballasts, ties and rails. The steel rails mounted on ties with fastening systems, indication to maintain the railway gauge, rails inclination, stability and lasting of the railroad. Keywords: dynamic tests, rubber plates, fastening, Centipede, MGCplus

Abstract: The present paper refers to the possibility of obtaining inorganic-organic nanohybrids, starting from nanoporous silica, in which the acrylonitrile template polymerization proceeds. In order to enhance the homogeneity between constitutive parts of the nanocomposite several methods were tested like increase of the imbibition period of the silica with the monomer, a better absorption capacity of the silica for the monomer and the use of the ultrasonication technique. The influence of the ultrasonic field on the template polymerization of acrylonitrile in inorganic structures was proved by FTIR and TG/DTG analyses. Ultrasonication was employed before the polymerization, in order to prevent the aggregation of particles, to well disperse the silica particles in the vinyl monomer and for a good imbibition. The results demonstrate that ultrasonication is effective in homogenizing the constitutive parts of the hybrid materials by yielding a fine microstructure of sintered nanomaterials. Keywords: inorganic-organic hybrid, porous silica, ultrasonication, template polymerization, nanocomposites

Abstract: The most appealing aspect related to nano-composites use, consists of their biomechanical properties; these properties succeed in giving good mechanical strength, a minimal polymerization contraction and an exceptional aesthetics and polish due to the features of the nano-filler. Investigating the effect upon both the filler level and the size of the filler particles on some experimental composites’ mechanical and physico-chemical properties, some authors have come to the conclusion that by increasing the filler level can be obtain first of all an increasing of the compression resistance and secondly a significant decrease of water absorption. The vast majority of the investigated composites, based on borosilicate glass, are showing an important increase of their resistance to wear together with the increase of the filler level. In this particular study the resistance to traction and respectively to fracture and also the structure (SEM) for some experimental nanocomposites (produced in our laboratory) and for a commercial product (Premise - Kerr Corporation) has been determined. The samples of material were made according to the ISO 4049 specifications; they were tested with the use of the Instron Universal Lloyd apparatus and the Scanning Electronic Microscope (SEM - FEI). Keywords: nanocomposites, physical properties, flexural strength, diametral tensile strength, SEM

Abstract: Two series of new self-coloured segmented polyurethane elastomers were successfully synthesized via the reaction of poly (tetramethylene ether) glycol (Terathane 1400) and hexamethylene diisocyanate / 4,5-dibromofluorescein with glycerine or castor oil as hard segments in a N,N-dimethylformamide solution. Polyurethane structure formation has been proven by infrared (IR) spectroscopy. Photosensitive-dibromofluorescein polyurethane elastomers exhibited high thermal stability and the addition of 4,5-dibromo-fluorescein in the preparation of the fluorescent polyurethane elastomers enhanced the tensile strength. This may be attributed to an increased cross-linking due to strong intermolecular interaction between the fluorescein polyurethane molecules. The fluorescence performance for the fluorescent polyurethane elastomers films appears at 560-580 nm, and increased concentration of 4,5-dibromofluorescein enhances the fluorescence performance of these polyurethane elastomers. Keywords: polyurethanes, fluorescence, chain extender, mechanical properties, thermal behavior

Abstract: The paper presents the experimental results regarding the investigation of some physico-chemical and structural characteristics of starch modified by electron beam and microwave combined treatment. The combined electron beam (EB) and microwave (MW) treatment of granular starch was performed in four different regimes, successive and simultaneous. The experimental data showed that the acidity of starch aqueous solutions increased while the apparent viscosity reduced as a function of the treatment parameters and regime. No significant changes appeared in the morphological characteristics of the samples treated with combined EB-MW, but the spectral characteristics suffered minor changes suggesting that the stability of hydrogen inter- and intramolecular bonds is affected. At the same time, the degree of order increased after successive combined treatments indicating some molecular associations or rearrangements in amorphous component of starch due to the microwave field. The evolution of the molecular weights and molecular weight distribution indicated that the macromolecular degradation cannot be correlated with the specific absorbed energy as a consequence of the microwave field contribution. Keywords: starch, electron beam, microwave, viscosity, SEM, GPC

Abstract: The thermal properties of a novel family of xerogels prepared from diepoxy-terminated poly(ethylene glycol)s of approximate molecular weights 600, 1000, 2000 and 4000 Da and various aliphatic polyamines (ethylenediamine, 1,4-diaminobutane, hexamethylenediamine, 1,8-octanediamine, 1,10-decanediamine, 1,12-dodecanediamine, diethylenetriamine, triethylenetetramine, tris(2-aminoethyl)amine) were studied by DSC and TGA measurements in order to establish the influence of several structural parameters that may affect the physical state of the network-forming polymer at a certain temperature. All xerogels synthesized displayed crystallinity which was affected by the MW of the PEG precursors, number of carbon atoms within the diamine chain, amine functionality and structure and amine/epoxy groups mole ratio. Both melting temperature and amount of crystalline phase were lower for networks with either shorter PEG chains, longer diamine chain, higher amine functionality and stoichiometric amine/epoxy groups ratio, while the thermal stability was higher for either longer PEGs, diamines with higher carbon atom numbers, higher amine functionality and stoichiometric amine/epoxy groups ratio. Keywords: networks; poly(ethylene glycol); aliphatic polyamines; melting temperature; glass transition temperature; thermal stability

Abstract: A method for obtaining, with low experimental effort, desired properties for road bitumen, was conceived. This method is applicable in those situations when the quality of the road bitumen is understandard, there are no physical interaction between the used components for modification and their concentration varies in very narrow limits. Keywords: physical modification, road bitumen, polymer, experiments design

Abstract: The thermal properties of nanofilled and microfilled restorative composites (Filtek Supreme XT and Filtek Z250) are studied in comparison with the ones of teeth. Our results show slightly decreased values of the thermal constants of Filtek Supreme XT with respect of Filtek Z250, due to the smaller filler particle size. Both analyzed composite materials have the values of the thermal conductivity and diffusivity very close to the one of enamel, with the better fitting in the case of Filtek Supreme XT. Comparing with the values for dentin, the thermal conductivity is about two times higher, while the thermal diffusivity is three times higher. Keywords: thermal properties, thermal conductivity, restorative composites

Abstract: The effect of clay-hybrids treatment on physical and structural properties of polypropylene (PP J600) nanocomposite has been studied. The experiments carried out were focused on obtaining the polypropylene nanocomposite samples. In all the experiments the polypropylene with flow rate in melt of 9.21g/10min and nanoblend MB1201 were used. The structure analysis of polypropylene nanocomposites was made by means of XRD and FT-IR methods. XRD analysis shows that for nanocomposite based on polypropylene, the exfoliation of organo-bentonites takes place. The results shows a high improvement in the mechanic properties of the NPP4 with 5% and NPP4 with15% glass fiber nanocomposite compared to the NPP4 nanocomposite. Keywords: nanocomposite, structure; diffraction, absorption, mechanical properties

Abstract: In this article we obtained the characteristic curves for polyester and epoxy resins used in the process of making composites, and determined their elastic and resistance properties as well as the characteristic curves on two directions for the epoxy and polyester resin composites, reinforced with woven polypropylene. We established the flow strain and two coefficients from the calculus relation for the plastic potential. We determined the equation of nonlinear dependency between strain and deformation in the plastic field using a fourth degree polynomial relation which indicates the specific elongation and resistance to fracture. Keywords: composite materials, polypropylene fabric, plastic field

Abstract: The polymers with special properties represent the starting point in order to obtain a wide range of new materials used in various fields of activity. Poly (methyl methacrylate) (PMMA), a transparent thermoplastic material, is an attractive polymer because of it’s unique properties, in comparison with other polymers, such as: high mechanical strength, special optic properties, and durability. The incorporation of silicate layers (for example, clay, minerals) in the polymer microstructure in order to improve the mechanical, thermal and interface properties has become one of the interesting of the researchers nowadays. Thus, depending on the working conditions and the interactions between the clay layers and the polymer system, a series of composites with different morphology, for instance, agglomerated, intercalated and exfoliated, has become accessible. In order to promote solutions for improving PMMA properties and to have a better general view on the action of oxide nanoparticles, we chose to analyze the structure and mechanical properties of some methacrylic composites with TiO2, Al2O3, and PMMA fillers. Keywords: nanocomposites, mechanical properties, poly(methyl methacrylate), SEM

Abstract: The paper presents a modern method to optimize welding procedures for PE 100 polyethylene pipelines using computer-assisted design of experiments. The design of experiments method RSD (Response Surface Design) was applied for optimizing the heated tool butt-welding of PE 100 type polyethylene pipes meant for pressure pipelines. Experimental researches made on 110mm diameter pipes had in view the mathematical modelling of the welding process, so that, on the basis of a number of 32 welding technological versions made, the optimum welding procedure was established, a procedure that met all the imposed conditions. Keywords: Optimizing, heated tool welding, polyethylene PE 100

Abstract: Flow through tubular runners presented is a very important flow type encountered in polymer processing, especially during injection mold filling. The filling pattern developed during the mold filling plays a decisive role on the final part quality, thus, in this paper we have investigated the filling pattern and the volumetric flow rate during the filling of a tubular runner for three different materials. The melt is treated as an incompressible, non-Newtonian the Ostwald-de Waele model with a power-law relationship between the shear stress and the shear rate. Keywords: runner, injection molding, flow front, polymer melt

Abstract: The paper aims to present a theoretical-experimental approach of a particular class of composite materials known as multiphase composites in order to retrieve its effective dynamic moduli and identify the major influencing factors on these variations. Supplementary, will be presented a two step homogenization concept based on the well known theoretical predictions from the micromechanics of composite materials approaches, the Mori-Tanaka that applies to the particle reinforced composites and Halpin-Tsai that applies to the random fibre composites. The theoretical values were compared with the experimental data, the later being retrieved during a two heating cycles with temperature ranging from -300C to 1600/2000C, in air, at a frequency of 1 Hz, using a DMA 242 C device, from Netzsch, Germany. The samples were manufactured using a self-developed technology. The samples were ceramics (Al2O3) and metal (Fe) reinforced particles embedded in small volume fraction along with random E-glass fibres (65%) into a polymeric matrix material. Keywords: composites, multiphase, polymer, dynamic modulus, testing

Abstract: The increasing of the field usage of high frequency (HF) welding joints technique of thermoplastic polymers gives advantages regarding productivity, quality of welded joints and high reproducibility of results. Base of experiments, this debate analyzes the main types of failure, the causes of the failure and the prevention method for HF welding of polyvinyl chloride PVC foils. Keywords: HF welding, polymers, failures

Abstract: 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

Abstract: 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

Abstract: 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

Abstract: 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

Abstract: 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

Abstract: 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

Abstract: 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

Abstract: 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

Abstract: The paper presents a comparative study on the structure of some polyvinyl alcohols used in PVC-S technology. The obtained data clearly showed that the degree of hydrolysis can be determined, with the same high precision through chemical method, IR and 13C-NMR spectra. The carbonyl content determined from the IR spectra also correlates with the carbonyl content determined from 13C-NMR spectra. A fast and reliable IR method for checking the degree of hydrolysis as technological support can be provided, the normalized carbonyl content determined from IR spectrum being linearly correlated with the degree of hydrolysis. Keywords: Polyvinyl alcohols, vinyl alcohol-vinyl acetate copolymers, IR spectra, 1H-NMR spectra, 13C-NMR spectra