Volume 50, Issue 3

Abstract: New copolymers having 2-anilinoethanol and N-sulfopropylaniline acid, as units in the main chain were prepared by cyclic voltammetry from 1M H2SO4 aqueous solution, and deposited on Pt and ITO electrodes using solutions containing different monomers ratios of 1:1, 1:2 and 2:1. The electropolymerization processes were carried out by sweeping the working electrode potential between 0.0 V and 1.3 V at 50 mVs-1, for 20 cycles. The copolymers were deposited as green layers on working electrode surface. All copolymers exhibit electrochemical activity in H2SO4 solution but they became unstable starting with the second cycle. Among all synthesised copolymers, only PAnEtOH-AnPS-12 shows electrochemical activity in acetate buffer solution, pH 6.5. Raman spectra recorded for PAnEtOH and PAnEtOH-AnPS-21 revealed the presence of the characteristic bands for polyanilines in both oxidized and reduced form. SEM and AFM micrographs revealed that the copolymers layers present a smooth and compact morphology with small roughnesses. It was evidenced that the change of the electrolysis medium pH induces changes in the morphology of the copolymers layers. Copolymers having both aniline monomers were obtained from acetate buffer solutions at pH 4.5 and characterized. Keywords: self-dopable polyaniline; sulfonated polyaniline; 2-anilinoethanol; electrochemical deposition; cyclic voltammetry

Abstract: The present work reports on the synthesis and biomineralization capacity of hydrogel networks composed of Bombyx mori silk fibroin, polyacrylamide and carboxylated multiwall carbon nanotubes soaked in simulated body fluid. Hydrogels were fabricated by the polymerization of acrylamide and N,N’-methylenebisacrylamide in silk fibroin solution containing carboxylated multiwall carbon nanotubes with potassium persulphate/triethanol amine redox system as initiator. The incorporation of the fibroin and MWCNT-COOH within the polymer network was proved by FTIR spectroscopy. Swelling measurements in saline solution were performed to evaluate the behaviour of these hydrogels having various compositions. Biomineralization assays in simulated body fluid solution showed the presence of apatite-like crystals onto the surface of the materials. Beneficial effects upon biomeralization process of the carboxylated nanotubes were further discussed. Mechanical compressive tests revealed good strengths for the silk hydrogels depending on their composition. The results of this study lay down the fundament for the use of these silk fibroin biomaterials in bone tissue engineering applications. Keywords: silk fibroin, carbon nanotubes, biomineralization, apatite, compressive strength

Abstract: The influence of various additives, like salts, alkohols, surfactants and water-miscible organic solvents, upon the cloud point of a, w - (2-hydroxyethoxy) oligo(propylene oxide) in aqueous solutions was investigated for the first time. The results showed that NaH2PO4, NaCl, NaBr, NaI, 1-butanol, ethylene glycol and dimethylsulfoxide decreased the cloud point, while 1,2-propylene glycol, sodium dodecylsulfate, nonylphenyl ethoxylated with 9 moles of ethylene oxide and dioxane increased it. Addition of N,N-dimethylformamide practically had no influence upon the cloud point on the concentration interval investigated. The LCST of a, w - (2-hydroxyethoxy) oligo(propylene oxide) in aqueous solution was also determined and it was found equal to 19°C. Keywords: a, w-(2-hydroxyethoxy) oligo(propylene oxide), thermosensitive polymers, cloud point, low critical solution temperature (LCST), additives

Abstract: Alkylation of benzene with bioethanol (95% and 100% concentration) has been done in a laboratory tubular reactor using a new modified zeolitic catalyst. The alkylation experiments have been done at different reaction temperatures , pressures and benzene/bioetanol molar ratio in order to establish their influence on the final composition of the reaction product, selectivity and conversion. The feed and products are analysed by gas chromatography. There was small differences between 100% bioethanol and 95% bioethanol aqueous solution in experimental alkylation results that it possible to use 95% bioethanol solution as alkylating agent. Keywords: alkylation benzene, bioethanol, ethylbenzene, zeolitic catalyst

Abstract: The vulnerability of ordinary Portland cement (OPC) concrete to acidic attack is a worrying subject regarding the future durability of this binder. On the other side of binder’s technology, the new technology of cement called ‘geopolymer’ had been studied widely in all over the world. Indeed, the major advantage of geopolymer compared to Portland cement is chemical resistance. This paper presents a study about the microstructural properties of geopolymer and OPC mortar. Visual inspection of both mortars had been performed. Stereo microscope device and Secondary Electron Microscope (SEM) were used to investigate the microstructural changes of the specimens. It was found that geopolymer mortars were less susceptible to the attack by sulfuric acid solution than the OPC cement mortars. Keywords: geopolymer, sulfuric acid attack, microstructural, SEM

Abstract: The effects of tensile and morphological properties of styrene butadiene rubber/virgin chloroprene rubber blends (SBR/CRv) and styrene butadiene rubber/recycled chloroprene rubber blends (SBR/CRr) were investigated. The range size of CRr used in this study was 0.3 – 0.7 mm. Both SBR/CRv blends and SBR/CRr blends were prepared using two roll mill at room temperature with blend ratios 95/5, 85/15, 75/25, 65/35 and 50/50. It can be observed that, cure characteristics of SBR/CRr blends have lower cure time, t90 than SBR/CRv blends.SBR/CRr blends showed higher scorch time, t2 and minimum torque (ML) compared to SBR/CRv blends at all blend ratios compared with the SBR/CRv blends. However, maximum torque (MH) of SBR/CRr blends exhibit the opposite trend compared with the SBR/CRv blends. It can be observed that, the tensile strength and elongation at break of SBR/CRr blends show higher value than SBR/CRv blends particularly up to 15 phr of CRr in the blends. However, SBR/CRr blends shows higher value of tensile modulus (M100) than SBR/CRv blends at all blend ratios. The scanning electron microscopy (SEM) of tensile fracture surface of SBR/CRr blends at 50 blend ratios illustrated a better adhesion and dispersion in comparison with SBR/CRv blends. Keywords: chloroprene rubber, recycled chloroprene rubber, styrene butadiene rubber, tensile properties, SEM

Abstract: Starting from the dynamic response of a sandwich beam with damping, (which is in free vibration), it is established a method used to determine the damping factor. We experimentally calculated the stiffness and damping factor per unit mass for beams with middle layer made of polypropylene honeycomb respectively; the external layers were made of epoxy resin reinforced with steel fabric. Keywords: sandwich beam, stiffness, damping factor, steel fabric, polypropylene honeycomb, free vibrations

Abstract: In the research paper we present a study regarding the road traffic safety and the ageing phenomenon of vehicle bumpers. For our study we used the accelerated ageing in conventional environment which is the most complex and comprehensive method to determine the bumper ageing. This method is used for plastic materials and comprehends ageing methods which simulates the natural exposes: taking into account the temperature, humidity and the presence of some chemicals, oils and fuels. Also, the method consists in the ageing of plastic materials which initially were conditioned in climatic chamber. The final evaluation happens when the object we study is tempering to the ambient temperature in the same climatic chamber (T = 23°C ± 2°C , UR = 50% ± 5%). Keywords: ageing, strength depreciation, stress, strain, rheology, fracture

Abstract: The paper presents the effect of poly (vinyl-phenyl-ketone) used as prodegradant for styrene-isoprene block-copolymers exposed at natural aging. Keywords: styrene-isoprene block-copolymers, poly (vinyl-phenyl-ketone), physico-mechanical properties, photo-oxidative degradation

Abstract: Romanian researchers, both dentists and engineers, are continuously involved to develop the knowledge concerning applications of different types of materials in restorative dentistry [1-4]. Only thus there is possible to be solved the main complex and interdisciplinary aspects targeting this large class of materials. Hence the present paper is focused on experimental studies of three glass ionomers taking into account their tribological behaviour in oral cavity under specific conditions. Keywords: glass ionomers, tribology, corrosion, restorative materials, dentistry

Abstract: In this article we present a new thermostat – theory and simulation results – obtained by combining two thermostats – Berendsen and DPD types. The new thermostat provides a predictable behavior with temperatures that do not deviate from the reference and with thermal rate constant agreement between simulations and theory. The presented work can be used for the study of polymer properties. Keywords: molecular dynamics, polymers, thermostats

Abstract: The chemical recycling of poly(ethylene terephtalate) PET using a unconventional method employing microwave radiation was studied. The reaction parameters were varied in order to study their influence. The reactivity of several glycols was compared and results showed consistency with conventional solvolysis methods. The dissolution of PET polymer into the glycol solution is one of the key parameters in determining the reaction time. The modification of the microwave field power afforded a 50% reduction of the reaction time. This method presents certain advantages compared to conventional glycolysis methods such as: energy and time saving through a rapid and a more uniform heating capacity, leading to a complete depolymerization in the presence of the catalyst. Keywords: PET waste, glycolysis, microwave, oligomers, viscosity

Abstract: The bonding materials used in orthodontics must resist to masticatory and active orthodontic forces. The aim of this study is to evaluate and compare the tensile bond strength of three orthodontic bonding procedures: acid etching and chemically cured macrofilled composite (Evicrol, SpofaDental, Jièin, Cehia), glass ionomer cement Ketac Cem (3M ESPE AG, Seefeld, Germany) and self-etching primer with light cure adhesive bond material (Transbond Plus Self Etching Primer + Transbond Plus Color Changer Adhesive, 3M Unitek, Monrovia, California). Moreover, after removing the brackets, the Adhesive Remnant Index (ARI) has also been measured. For this purpose 30 recently extracted human premolars were used, grouped randomly in three groups, 10 teeth for each tested material. After bonding the brackets, these were torn off from the teeth surfaces with a tensile testing machine (Instron 1195). The ultimate tensile strenght (UTS) and the ARI has been measured. Our conclusion was that glass ionomer cement fails first to the tractioning forces, while light cured composite has proven to resist best to streching and traction. Although light-cured composite has failed to lower forces than the chemically cured one, the frequency of ARI score 3 has been the highest, which means that its adhesion is the best. Key words: tensile bond strength, bonding material, adhesive remnant index

Abstract: The purpose of this paper is a radiological evaluation of the prosthetic polyethylene component wear in time (years), a quantification of this wear depending on the different types of prostheses and a correlation between the degree of wear and the radiological signs of deterioration of the periprosthetic bone structures, resulting in mobilization of the prosthetic components (loosening). Keywords: polyethylene, hip prosthesis, particle disease, loosening

Abstract: In this paper are presented structural parameters that influenced the metachromatic phenomenon induced by two maleic acid copolymers in form of sodium salts, as anionic partners. One is hydrophilic, namely the copolymer sodium maleate-vinyl acetate, (NaM-VA), and the other is a hydrophobic one, namely sodium maleate-styrene copolymer (NaM-S). The cationic dye was Methylene Blue. The correlations between UV-Vis spectrum data and those of spectral remission are also discussed. Keywords: maleic acid copolymers, Methylene Blue, metachromasy, Melana fiber, spectral remission, K/S values

Abstract: Asphalt nanocomposites were prepared by mixing nanoparticles of calcium carbonate with a solution of bitumen in xylene in the presence of a solution of polymer in xylene. Calcium carbonate nanoparticles were obtained by wet milling and their characterization was performed by dynamic light scattering (DLS). The polymers used were either polyacrylate type and polystyrene homopolymers or copolymer of polyacrylate-polystyrene type synthesized by solution process. Asphalt nanocomposites prepared were characterized by dynamic mechanical analysis (DMA). The results indicate a close behaviour of nanocomposite based on polyacrylate and polystyrene homopolymers and polyacrylate-polystyrene copolymer. Keywords: asphalt nanocomposites, calcium carbonate, dynamic mechanical analysis

Abstract: Thin films of polyamide 6 (with various concentrations) were deposited by spin-coating method (at various rotation speeds) and surface morphology of these films was analyzed by scanning electron microscopy. Following this analysis it was revealed that deposited film thickness depends on solution density, its viscosity, rotation speed and rotation time. In the context of multi-scale type theories, a theoretical model which explains our experimental results is established. Keywords: spin-coating, polyamide, thin film, multi-scale theory