Volume 50, Issue 4

Abstract: The study of modification by melt alloying of recovered polypropylene with styrene and a-methylstyrene-diene block-copolymers is presented in this paper. The block-copolymers were synthetized with the same composition and molecular weight in order to relieve more accurately the influence of the component block nature upon the modification degree of the polyolefin. It was found that only the nature of the diene block has a significant influence on the intensity of the modification degree for recovered polypropylene. Keywords: recovered polypropylene, styrene-isoprene block-copolymers (SIS), styrene-butadiene block-copolymers (SBS), a-methylstyrene-butadiene block-copolymers (aMeSBaMeS)

Abstract: Cellulose and polyhydroxyalkanoates, polymers from renewable resources, have been intensively studied for the last decades and they are the main topic of this paper. Bacterial cellulose pellicles (BC) were synthesized in static culture fermentations and ultrasounds were used to disintegrate them into fibers (us-BC). Microcrystalline cellulose (MCC) and us-BC were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and infrared spectroscopy (ATR-FTIR) with a view toward their use in fully biodegradable and biocompatible polymer composites. Mechanical properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) modified with the two types of celluloses were also investigated. AFM images showed that big aggregates of BC fibers disappeared after ultrasound treatment but small aggregates coexist with separated fibers in us-BC sample. Higher XRD crystallinity and crystallite dimension were obtained for us-BC as compared to MCC. Mechanical tests on poly(3-hydroxybutyrate-co-3-hydroxyvalerate), neat and modified with the two cellulosic fillers, showed that the highest values of tensile strength and modulus were obtained in the case of the composite containing us-BC. Keywords: bacterial cellulose, polyhydroxyalkanoates, XRD, polymer composites, AFM

Abstract: The paper presents experimental data regarding organic modified silica hybrids having embedded a non-ionic dye – Disperse Red 1, deposited on cotton fabrics. Hybrids were prepared by sol-gel processes using tetraethoxysilane and various trialkoxysilanes as organic network modifying agents, in acid catalysis and in the presence of Disperse Red 1. Control of the interactions between the organic non-ionic dyestuff and its embedding matrices allows tailoring the performance of the resulted coatings. Light and wash fastness and thermo-mechanical properties of the coated fabrics were investigated and correlated to the composition and morphology of the organic-inorganic coating materials. The results show that chemical composition of the impregnating bath have a decisive role in determining shade, intensity, fastness to light or washing of the coloured hybrid coatings as well as thermo-mechanical and hydrophobic properties of the coated textile fabrics. Keywords: silica hybrids, non-ionic dye, cotton fabrics, contact angle, thermal stability

Abstract: This paper presents new composite materials used in extension of growth season of vegetable crops, in countries with a mild continental transition climate, for constructions type tunnel. Composite materials are realized from two components, namely textile materials with generated heat potential and polyethylene polymer foils, with a selection possibility of wave lengths in IR domain. For insurance of microclimate conditions, especially of thermal performance, the materials have been tested from electrical and mechanical point of views, following the generated heat flux and its elastic deformations for a known material width. Keywords: tunnel, horticultural crops, composite materials

Abstract: Rubber is widely used for rolling stock and railway infrastructure parts. Rubber plates are used for rail – sleeper fastening systems and rubber parts are used for primary suspension of the Romanian (and abroad) electrical locomotives, of metro (underground) trains, of tramways; at tramways wheels are made as metal – rubber assembly with the purpose to minimize the unsprung mass. From above examples, it easy to see that rubber parts are used in railway field as elements which are directly involved in safety of circulation. Keywords: tests, locomotive, primary suspensions, rubber-metal

Abstract: The wide band dielectric spectroscopy analysis of the 1.5% multi walled carbon nanotube (MWNT) contain and 20% polyamide 6 (PA6) nanowebs obtained by three different treatments applied to the MWNTs (chemical, mechanical and mixed) was investigated. A morphological analysis of the samples was carried out using the scanning electron microscopy (SEM) and atomic force microscopy (AFM) principles. The evolution of the dielectric constant (Eps’), imaginary permittivity (Eps”), dissipation factor (Tan d) and the conductivity modulus were analysed, both from an experimental and a theoretical point of view. Keywords: nanowebs, polyamide 6, multi walled carbon nanotubes, wide band dielectric spectroscopy

Abstract: In this paper, data on Melana-type polyacrylonitrile fibers dyeing with Methylene Blue in the presence of maleic acid copolymers with vinyl acetate or styrene are presented. Mathematical models of the studied dyeing processes have been developed and the necessary information on their significant factors are produced by means of experiment planning methods, known as Design of Experiment (DoE) or Experimental design. Optimal correlations between the application conditions and the color differences obtained on Melana fiber type have also been studied. Keywords: polyacrylonitrile fibers, dyeing, maleic acid copolymers, Methylene Blue, methods of planning experiments (DoE), color differences

Abstract: Monitoring of bone fracture healing evolution is performed in practice by repeated radiographic examination. We describe the use, on a clinical case of tibial diaphyseal fracture, of a method that records in progress the change of basic frequency of the healing fractured bone segement compared with the uninjured one. We ascertain an increasing evolution of the basic frequency of the fractured tibia tending to the values of parameters recorded in the unfractured segment. Approximately 100 days after trauma the recorded values enter the plateau phase, tending to those recorded contralaterally, which overlaps the healing period seen in practice. We, therefore, show the possibility to monitor the evolution of a diaphyseal bone fracture healing by the means of vibrations. Keywords: basic/main frequency, tibial fracture, biocompatibil material, accelerometer, bone healing

Abstract: The elastic contention is the most efficient and used method to solve chronic venous insufficiency, being used in some countries by 71% of patients. In functional design of knitted orthoses with increased elasticity which exert a controlled pressure on a cylindrical surface of human body, used in the treatment of venous insufficiency, the model proposed allows optimal assessment of pressure values in knitting - anthropometric sizes - applied pressure ratio. Therefore starting from mechanical behaviour described by stress-strain diagrams of knittings from polyurethane yarns and using the pressure formula based on the model proposed we can assess accurately the applied pressure values for different anthropometric circumferences. Based on the model it was determined the calculation ratio of pressure exerted by the knitting versions for the cylindrical model embracement of different parts of human body. The choosing of orthoses is a difficult problem, few patients can find serial orthoses which fit the patients’ limbs configuration. Hence, the model can be used easily for designing and manufacturing on demand of the orthoses with controlled pressure potential. Keywords: graduated compression stockings, pressure modelling, stress-strain diagrams, chronic venous insufficiency, knitted fabrics, polyurethane yarns

Abstract: The paper presents a case study on the causes that led to the breaking of the blades on a 5 kW wind turbine due to high wind loads at a wind speed of 30 m/s . The paper is structured in two parts. In the first part there are presented the functional design and material aspects essential for a blade proper operation, with an analysis of the critical areas where the breaking of the blade was initiated. There are also analyzed the causes the materials prescribed in the technical design and the manufacturing technology failed upon a short time wind gust of up to 30m/s. In the second part of the paper there are presented corrective technical solutions for materials and blade shape design in order to ensure a higher mechanical strength of the blade suitable for a safe and reliable operation for the specific environmental conditions. The studies and the solutions considered for the blade design improvement shown in the present paper are based on finite element analysis (FEA) as well as on blade static tests performed by using distributed sandbag loads. Keywords: wind turbine, blade, wind speed, GFRP, Finite Element Analysis, load, stress

Abstract: The purpose of this „in vitro” study was to evaluate the retentive force of the bar/rider attachement system in 4 situation and to compare their fatigue behaviour after consecutive insertion-removal cycling. Keywords: retentive force, bar/rider attachement system, fatigue

Abstract: A number of epidemiological, clinical and experimental studies show that cholinergic stimulation induced by the contact between human body and several plastic materials plays an important role in the pathogenesis of diseases. Extraneuronal acetylcholine mediates the reduction of cytokines synthesis, the increased synthesis and release of histamine from dermal mast cells or basophils, and the suppression of the inflammation. Based on these considerations, the authors proposed to verify the importance of acetylcholine in the mechanism of generation of the inflammatory response, using Helicobacter pylori infection as an experimental model for systemic inflammation. We also studied the impact of antihistamines/anti-Helicobacter pyori treatment on acetylcholine levels in chronic idiopathic diseases. Determination of the inflammation tests and the cholinesterase activity, as the level of non-neuronal acetylcholine, showed a significant association between cholinesterase activity, inflammatory response and therapeutic efficacy. In conclusion, evaluation of the inflammation tests and the cholinesterase activity could be an adjuvant factor for therapeutic management in chronic idiopathic diseases subjects. Keywords: plastic materials, inflammatory response, non-neuronal acetylcholine, cholinesterase activity

Abstract: Polymer composites from polypropylene (PP) and treated and untreated hemp fibers (HF) were prepared using a twin screw extruder and separated feeding ports. Both treated and untreated HF show reinforcing effect in PP composites but the treatments applied to HF accentuate this effect. An increase with 78 % of tensile strength and with 61 % of Young’s modulus was obtained with untreated fibers and double tensile strength and modulus when using treated HF. Aminosilane treatment of HF was the most efficient, leading to simultaneous improvement of tensile properties and impact strength of PP composites. Keywords: hemp fibers, mechanical properties, twin screw extruder, polymer composites

Abstract: The paper presents our results with polymethylmethacrylate cement augmentation osteosynthesis around the knee joint and to discuss the advantages and complications encountered. We presented the benefits and limitations of cement augmented fixation constructs around the knee because of the lack of such studies that focus on this particular anatomical location. We consider that the cases described can contribute to a greater understanding when searching for solutions targeted on the knee defects. In conclusion, we find polymethylmethacrylate cement augmentation of implants to provide excellent fixation around the knee both for tumoral resections as well as for managing complex trauma cases. Keywords: polymethylmethacrylate spacers, osteosynthesis, knee joint

Abstract: This paper presents the study of sorption kinetics and thermodynamic equilibrium of chloroform and methanol sorption in thin polyvinyl acetate (PVAc) films. Experiments were conducted on a laboratory set-up using a pressure-decay technique. The obtained data were compared with other literature data obtained using other experimental method and are in good agreement. Comparison between the actual experimental and other literature data obtained using different investigation techniques are in good agreement. Keywords: polymer films, solvent sorption, pressure-decay technique

Abstract: The objective of our study was to assess the “in vivo” wear of cross linked polyethylene in contact with different materials surfaces. Thus, we compared the polyethylene acetabular cups wear when they function in a couple with ceramicized metal heads (zirconium oxide) with those in a couple with cobalt chromium metal heads, in total hip arthroplasties. The polyethylene wear was quantified by digital measurements on standardised digital front and lateral view X-rays and the differences were statistically analysed. Keywords: ceramicized metal, polyethylene, hip prosthesis

Abstract: Nowadays, the growing environmental awareness throughout the world has triggered a paradigm shift towards designing environmentally friendly materials. The interest in cellulose fibers as reinforcement agents in composite materials with polymer matrices has increased dramatically in the last decades, the main reasons associated with this upsurge being their renewable and ubiquitous character, good mechanical properties, low density, low cost and recyclability. Focus on dielectric spectroscopy technique, the article makes a comparison between the dielectric properties of transformer board and composite materials obtained by mixing recycled polyethylene with wood powder or lignin in different percentages. Keywords: recycled polyethylene, transformer board, dielectric spectroscopy analysis

Abstract: The present study makes a comparative study of various cylindrical assemblies using the analytical models developed by minimizing the potential energy associated with the stress field and using variational methods and some assumptions. All the components of the stress field were defined function of the s(1)zz(z) stress in the first element and then introduced into the potential energy formulation. A variational method applied on the potential energy of deformation help us to obtain the minimum. This applied model can predict the optimal overlap length. Finally, a failure criterion of Tsai-Hill type was established. Keywords: stress analysis; stress distribution; adhesive joints; analytical method

Abstract: In order to design/redesign an optical sighting device used on an automatic weapon, several issues related to the behaviour under loads that appear during shooting should be taken into account .Also, in order not to influence the effectiveness of the weapon, the mass and the volume of the device must be as small as possible. In this paper, a comparative analysis of the behavior of the the ensemble sighting device - clamping system, subject to inertia forces is undertaken in the following two cases: the ensemble parts are made of duralumin and, in the second case, of polyester resin. The study is performed by means of numerical calculus, on the model being applied an acceleration in steady state mode. Keywords: sighting, optical, finite element, plastic material

Abstract: For this study the creams, based on collagen or lanolin and active principles from: Viscum album, Ocinum basilicum, Rosa canina, for cosmetical and medical use, were prepared. The active principles from the obtained vegetal extracts were identified on classes and / or compounds by spectrophotometric and chromatographic methods. The choice of the active components, from the selected plants, that will be included in the creams was performed depending on their biocompatibility with the derma and on the obtaining of some complexes with the collageneous protein, with high content of bioactive substances. The biocompatibility was intended to evidence the tolerance and the affinity between the biopreparation and the coetaneous constituents. This affinity was correlated with the biological origin of various used compounds, generally, with the ones which exhibit resemblance or even similarity with the derma constituents. Keywords: creams, collagen, vegetal extracts, biopreparations

Abstract: The study aims at analysing the effect of the glass microfiber content on the variation of the cutting forces in the orthogonal turning process of two types of polytetrafluoroethylene: PTFE and PTFE S25 (25 [wt%] glass microfibers) with a polycrystaline diamond (PCD) tool. The influence of the process parametres (cutting speed and feed rate), as well as that of the geometrical parametres of the cutting part of the tool (rake angle g when the clearance angle a and the incidence angle c are constant) on the two components of the cutting force (cutting force, Fz, and feed force, Fx). The values of the turning forces were recorded with a Kistler piezoelectric dynamometer (type 9257B). Experimental results indicated that the value of the cutting force decreases with the increase of the cutting speed. Moreover, the glass microfiber content influences the value decrease of the main cutting force component. A statistical mathematical model, determined by linear regression, was developed to analyze the influence of varying parametres on the cutting force components (Fz and Fx). Keywords: PTFE, orthogonal cutting, cutting force, PCD tool

Abstract: The paper presents experiments on developing new materials with preset properties for the footwear area, particularly for customized footwear. Research focused on analyzing a rubber plate formulation for heel tops commonly used in footwear manufacturing, varying the amount of filler and expanding agent in different proportions to obtain physico-mechanical properties appropriate for use. In this paper, the purpose of research was developing customized footwear by reducing the Fy mediolateral component of the ground reaction force when the foot touches the ground during walking. Developing customized footwear taking into account ground reaction force aims to improve walking or static position. In order to fulfill its role, footwear must reduce the Fy mediolateral component of the ground reaction force. Lately, reducing ground reaction force has been a major concern in footwear design and manufacturing. Ground reaction is measured using AMTI’s AccuGait System force plate. Keywords: cured rubber, customized footwear, ground reaction, force platform

Abstract: The aim of this paper is the study of the influence of some solvents on the electronic absorbtion spectra of B12 vitamin by using the cell model of pure liquid proposed by Takehiro Abe. The radius of the first and second solvatation sphere, the number of particles from the first two solvatation sphere were calculated and then it was estimated the potential interaction by dispersion forces between the spectrally active molecule (vitamin B12) and the solvent molecules which surrounded it. The linear dependence between a and b Abe coefficients permits to estimate the polarizability and the dipole moment of the spectrally active molecule (B12 vitamin) in the first excited state. Some electrical parameters were calculated after Langevin dynamics applied to investigate system. Keywords: Vitamin B12, electronic absorbtion spectra, polarizability in the electronic state, Langevin dynamics, total energy