Volume 47, Issue 3

Abstract: The paper proposes new structures to replace the polystyrene, which is well known to be a toxic and inflammable material, non-biodegradable, used on a large scale for residence and civil thermal insulation and for packaging. The proposed structures are intended to be light structures, easy to manipulate, easy to be cut at the sizes needed, compact enough to not be damaged during the transport or during the mounting time, easy to fix on the building walls and of course with similar thermal insulating properties as polystyrene. First agglomerated composites were proposed. The materials used in these structures are green and biodegradable, found as inserts of wood (flakes or fibers) and textiles (wool or jute) and binders as wheat flour, clay or ecological acrylic copolymers. The density and thermal conductivity coefficient were determined for each structure and compared with the expanded and extruded polystyrene values and finally the more appropriate structures were recommended. To some of the structures flakes of polyethylene were added, in order to constitute a steam barrier of the new product. The addition of the polyethylene proved to be a disadvantage for the thermal insulation property of the structure and also for its compactness and reliability. The agglomerated composites mentioned above were pressed at a normal temperature (20-22oC) and conditioned at a temperature of 40-50oC. Two other structures were also proposed in this paper for the same purpose: a sandwich one, obtained after pressing it at 200oC, containing jute, wood fibers and polyethylene granules for the core and beech wood veneers for the faces and a panelled board made of waste of polyethylene and jute core and fiberboard faces. Keywords: polystyrene, polyethylene, thermal insulation density, composites

Abstract: The new materials have physical and mechanical properties that allow their processing by using classical methods, specific for synthetic polymers. In vitro biocompatibility studies were performed on a primary culture of human dermal fibroblasts by the MTT test. The biocompatibility of the materials was tested in vitro by determining cell viability in a culture of human dermal fibroblasts by using the MTT method. The physical and mechanical properties and also the biocompatibility properties of the new materials recommend them to be used in the manufacture of medical devices. Key words: synthetic polymers, natural polymers, blends, polyvinyl chloride, collagen, elastin, biocompatibility, cell viability

Abstract: The paper directs the attention to the detrimental influences exerted by longitudinal notches on the polyethylene pipe surface when subjected under high pressure to long time service. It was shown that the detrimental degree is influenced by the notch depth, working pressure and service duration. Depending on these parameters, researches evinced two types of fracture behaviour: ductile and brittle. The conditions they produce and the transition limits of the ductile – brittle behaviour were demonstrated in two different environments: water and air, at the temperature of 80°C. Keywords: mechanical behaviour, testing duration, environment, PE 80 polyethylene, pressure, longitudinal notches, temperature, pipes

Abstract: Most of the Romanian treatment stations use surface waters to obtain potable water. Suspensions elimination is achieved though coagulation with aluminium sulphate or with aluminium polyhydroxychloride. These chemical reagents contaminate the potable water with aluminium ions, which may lead to different diseases of the organism. This paper focuses on a comparative assay of different coagulation agents or coagulation/flocculation agents based on laboratory studies or purification stations. In the same time we propose a new ionic polymer as flocculation agent. Keywords: coagulation/flocculation, polyelectrolytes, potable water

Abstract: The birefringence of some polymeric esters of alkoxy benzoic acid (PEABA) in tetra chloromethane (TCM) was determined by previously proposed interferometric methods in polarized light. An increase in PEABA birefringence when an external electric field acts on the liquid crystal layer was evidenced in this paper. The decrease of PEABA birefringence with the increase in the alternate electric field frequency was also evidenced. The dipolar nature of the collective interactions between the side-chains of PEABA in liquid crystalline phase and also the viscosity of the lyotropic liquid crystal obtained by mixing PEABA with TCM in concentrations of about 10-2 g / cm3, at room temperature are sustained by the results obtained in this paper. Keywords: PEABA birefringence, tetra chloromethane (TCM), polarized light

Abstract: Extracellular matrix biocomposites based on poly(ester urethane), and hydrolyzed collagen, elastin, chondroitin sulfate and hyaluronic acid have been prepared. Different surface morphologies for each of the test matrices were revealed by Environmental Scanning Electron Microscope (ESEM). The biological material used is a very wide spread aggressive fungal species in all media for life, Mucor mucedo. Evaluation of the biologically active potential of these biocomposites against Mucor mucedo has been done through inoculation onto Sabouraud –agar nutrient medium. Fungal growth was monitored over 60 days.Visual observations of the fungal growth show that Mucor mucedo was aggressive and caused rapid grow after 72 h of inoculation onto Sabouraud-agar nutrient medium, but the biopolyurethane composites samples relatively to the fungal attack particularly showed a different relationship. Keywords: biomaterials; composites; polyurethanes; Mucor mucedo; extracellular matrix

Abstract: In the context of developing new phosphazene/silica hybrids for preparation of thermally resistant membranes for gas separation processes, two cyclophosphazenes/organosiloxane monomers (1 and 2, scheme 1) were synthesized via aminolysis of hexachlorocyclotriphosphazene (N3P3Cl6) with the monoamine functional trialkoxysilanes: 3-(triethoxysilyl)-propylamine (H2N-(CH2)3-Si(OC2H5)3) or 3-(trimethoxysilyl)-propylamine (H2N-(CH3)3–Si(OCH3)3), respectively, as new starting compounds for cyclophosphazene/SiO2 composites prepared by the sol-gel process. The siloxane monomers, N3P3Cl3[N(CH2)3Si(OCH3)3]3 (1) and N3P3Cl4[N(CH2)3Si(OCH2CH3)3]2 (2), as well as the corresponding composites {N3P3Cl3[N(CH2)3]3}y-(SiO2)41y (1’) and {N3P3Cl4[N(CH2)3]3}y-(SiO2)80y (2’) issues from the sol-gel process, have been characterized by infrared spectroscopy and elemental analysis, TG-DTA-DSC coupled thermal analyses, as well as by XPS, XRD, and SEM-EDAX investigations. Keywords: cyclophosphazene, sol-gel process, organic-inorganic hybrid materials

Abstract: This paper presents the synthesis and characterization of a new class of biodegradable copolymers based on carbohydrates. A new oligomer was synthesized by the polycondensation of 1-benzyl-5,6-(bis(maleyloxy))-2,3-isopropylidene-D-mannofuranose with propane-1,3-diol in the presence of p-toluenesulfonic acid and then it was copolymerized with 2-hydroxypropyl (meth)acrylate, using benzoyl peroxide as initiator. The mannose based oligomer was characterized by FTIR and NMR spectroscopy and HPLC-MS, and the copolymers were analyzed using FTIR and thermogravimetry. Keywords: D-mannose, glycopolymers, maleic anhydride

Abstract: The effects of UV exposure on physico-chemical properties of polymer membranes were studied in this paper. The membranes having different surface energy, resilience and initial modulus of elasticity were obtained from a series of blends of poly (hydroxy-urethane) and poly (vinyl alcohol). UV treatments in air, at room temperature, decrease the water contact angles as a result of higher surface energies of the polymer membranes. Some important modifications appear in ATR-FTIR spectra. The mechanical properties of the untreated polymer films are better than of the UV treated samples. Short-term UV irradiations lead to a photo stabilization effect of polymer surface. Bulk chemical changes are induced through photo oxidation and photo degradation processes for long-term UV irradiation. Keywords: UV treatment, photo oxidation, photo degradation, photo stabilization resilience

Abstract: In this work, different types of neural networks and modeling methodologies are used and compared: feedforward and recurrent networks, stack neural networks and a hybrid model composed from a simplified phenomenological model and a neural network. For each situation, the performance of the networks was evaluated through mean squared error and correlation between training data and neural network predictions. Accurate results were obtained with different types of neural models, but our approach recommends feedforward neural networks which are simple to train and use. The well known free radical polymerization of methyl methacrylate, accompanied of gel and glass effects and achieved in a batch bulk process is considered as example. In a hybrid methodology, the kinetic model used until the onset of the gel effect is associated with a neural model which replaces the diffusional effects representing the difficult part to model in the process. Keywords: neural networks, free radical polymerization modeling, polymethyl methacrylate, hybrid model

Abstract: Since discovered, rubbers were tested, among other possible utilizations, for their military use. In the present study, NBC protection properties of a new bromobutyl rubber-based composite (BrBR) are presented: protection time against liquid droplets of mustard gas (also known as yperite, 1,5-dichloro-3-thiapentane or HD), flame resistance and flame propagation properties. The tests performed demonstrated the improvement brought by BrBR in comparison with the materials in use in the Romanian army, this material offering the same protection level as the materials used nowadays in developed countries. Keywords: NBC protection, composites, mustard gas, burning time

Abstract: Photoluminescent composite of poly-ethyleneterephtalate-SrAl2O4: EU2+, Dy3+ was prepared by of a new procedure based on mixing the constituents in specific solvents for PET. In a first step it was studied the possibility of preparing europium and dysprosium doped strontium aluminate using a method that allows obtaining crystals in nanometric range compatible with polymer matrix. Also, the dependence of transparency in UV-VIS range of the polymer matrix density and experimental paths for obtaining a low crystallinity of PET at co-precipitation from solution were investigated. Characteristics of absorption / photonic emissions, phosphorescent decay time were investigated for europium/dysprosium doped strontium aluminate, and respectively for the composite prepared. The prepared photoluminescent composite presents a series of applications in optoelectronics, highway/ railway and utilitarian signaletics. Keywords: long persistence phosphorescent compounds, phosphorescent composites, polymer matrix, polyethyleneterphtalate

Abstract: The three-dimensional printing is a rapid prototyping technology, used to create complex three-dimensional parts directly from a computer model of the part, with no need for tooling. This paper investigates the use of a modern RP technology known as 3-D printing. Using the Rapid Prototyping 3D Zcorp 310 Printer system, we manufactured the prototypes for orthopedic adaptive modular plates based on intelligent materials, human bones and an artificial hand necessary for ‘in vitro’ simulations, experimental tests, experimental measurements. The material used is a High performance composite powder Zp131. After printing, we used Z-Max Resin - High Strength Epoxy Infiltrant System to provide strength and impart specific properties. Using Rapid Prototyping as a fabrication method one can finally obtain functional assemblies. Experimental studies of the staple made of the shape memory alloy named Nitinol are presented. The complexity of the shapes and dimensions of the fabricated parts recommends Rapid Prototyping method as a future fabrication method in different applications and scientific fields of research. Keywords: CAD-CAM, rapid prototyping, 3D-printing, Nitinol, composite powder, epoxy resin, orthopedic applications

Abstract: This paper presents the research performed in the laboratory of Renewable Energy Sources within the Petroleum-Gas University of Ploieºti regarding the use of heat pumps for surface geothermal energy extraction. The paper also examines the decrease of thermal power extracted via heat exchangers mounted in the soil, due to the cooling of the surrounding soil. The results obtained for a simple U-shaped loop mounted in a vertical shaft are presented as well. Keywords: thermal decline, Geoexchange, polyethylene, heat pump, numerical models

Abstract: Collagene-based nanocomposite membrane films were obtained by dispersing nanohybrides formed by modifying a layered silicate with quebracho and methylene blue in a collagen-gel matrix. TGA and XRD analyses proved the intercalation of active substances between the silicate layers. Thermal stability of the binary nanohybrides decreases with the increase of active substance content. Nanocomposites showed an improved thermal stability compared to collagen. Modifying the silicate with active substances influences the hydrophilicity of final nanocomposite by reducing the water vapour adsorption. Although the methylene blue is a disinfectant, it influences negatively the growth and development of the fibroblasts hence it is inappropriate for use in case of an open lesion. Quebracho is biocompatible and has a biostimulating effect on the growth and development of the fibroblasts, bioactive films thus obtained being good antiseptic and regenerating patches. Keywords: nanocomposites, montmorillonite, collagen, methylene blue, quebracho

Abstract: A biodegradable blend based on low-density polyethylene (LDPE) and 36 % starch that can be used for horticultural application was studied. The mechanical properties and the processing by molding injection were also studied. It is found that the starch helps to increase surface area on which the microorganism can attack the polymer matrix. The increase in the carboxyl index, which indicates the concentration of carboxyl blend, with time, also indicates the progress of biodegradation. Although this type of blend is not completely biodegradable it is preferred to those completely biodegradable which are expensive and with many processing problems. Keywords: biodegradation, starch, polyethylene, blend, application

Abstract: The paper presents the experimental results obtained for the Necuron 1020 rigid polyurethane specimens with stress concentrators, at traction test. The resistances of these specimens are evaluated based on the critical distances theory, obtaining a good agreement with the experimental results. Keywords: rigid polyurethane, the critical distances theory

Abstract: The paper shows in its first part the role, efficiency, types, factors and mechanisms of using the synthetic polymeric flocculants in the paper industry. The experimental part shows the research carried out to determine comparatively the efficiency of using the single component retention systems, with micro/nano particles in the modern alkaline paper production compared to the conventional acid process. Keywords: paper, flocculation, retention aid, zeta potential, micro/nanoparticles

Abstract: When the plastic materials products are obtained by injection into the mould, the fluid plastic mass takes the shape of the cavity and then, in a technological time, the obtained product cools until a temperature which makes possible its unloading without any deformation. Each product or more products may be realized during a period which means the time of one manufacturing cycle. An optimum manufacturing process is a continuous process without waiting times. The paper presents a methodology for the calculation and adjustment of some injection parameters which influence the time of one manufacturing cycle for the plastic materials products realizing. Keywords: plastic materials manufacturing, thermal processes of the polymers injection

Abstract: The new organic coatings were realised from polyurethane resin and alkyd+melamine-formaldehyde resins. The electrochemical techniques of the electrochemical impedance spectroscopy (EIS), cyclic potentiodynamic polarisation and linear polarisation were applied and the tests were carried out in a normal aerated 3% NaCl solution at ambient temperature. Also, open circuit potentials in 3% NaCl solution were monitored for 300 immersion hours. Salt spray tests were carried out according to ASTM B117 Standard. An electric equivalent circuit with two time constants representing the barrier characteristics of the intact organic coating, and the corrosion process occurring at the substrate/paint interface was fitted. The both coatings revealed very good protective properties, assuring a very good resistance for about 8 years in the ambient environment. Keywords: protective films, immersion tests, salt spray tests, EIS, cyclic polarisation

Abstract: Due to the multitude of restorative materials on the today market, the studies presented in this paper come to make some contributions regarding the evaluation of biomaterials in terms of resistance to the wear process, the factors influencing the tribological behaviour of hard structures and restorative dental biomaterials in the oral environment. Keywords: composite materials, tribology, wear, dental medicine

Abstract: The paper presents results on wear after testing a class of composites (PA +1% black carbon and different 5 concentrations of micro glass spheres) and discussions about damaging processes within the superficial layer, grouped in two categories: one favouring the material remove and the other the reduction of wear intensity. The analysis points out that tribological behaviour should be interpreted only by putting together information about wear, friction, temperature in contact, pair of materials in contact in order to obtain sustainable results that could be useful in engineering design. Keywords:micro-nano particles, polyamide, wear, IR thermogravimetric, SEM