Volume 50, Issue 1

Abstract: It was evaluated, in vitro, the effect of different artificial saliva on the mechanical properties of elastomeric ligatures. A total number of 160 elastomeric ligatures were divided in four groups (n=40 in each group). Three groups were exposed to three types of artificial saliva, (unmodified artificial saliva, with coca cola and with topical fluoride agent), for a period of 28 days. The fourth group (control group) remained unexposed. Tensile load at failure was determined by stretching the ligatures using an Instron Universal Testing Machine, until they fractured. The obtained data was statistically analyzed at a level of significance (p < 0.05). The two-way ANOVA showed significant statistical differences within groups (p < 0.001) and between time intervals (p < 0.005). There were a statistical significant interaction between groups and time on tensile load at failure (p < 0.005). Artificial saliva, Coke and Topical Fluoride seem to cause an increase in force decay of elastomeric ligatures, with a decrease in tensile load at failure over time. Keywords: elastomeric, orthodontics, tensile load

Abstract: Polymer materials for denture bases, with thermal or light polymerization are relatively fragile, being considered brittle materials from the Fracture Mechanics concepts point of view. This paper presents a comparative study on determination of fracture toughness for 2 types of resins used in complete dentures technology: heat-curing resin (Meliodent), and light-curing resin (Eclipse). The tests were performed on a static loading machine, model Zwick/Roell of 5kN. The results obtained by 2 methods differ no more than 10-15%. Both methods showed that Eclipse has a better resistance to fracture than Meliodent. Keywords: acrylic resins, complete dentures, fracture toughness

Abstract: The paper presents a study on the waste polypropylene modification with styrene-isoprene block-copolymers in correlation with elastomers molecular weight. The modification of this polyolefin improves the mechanical properties, especially the impact strength. Keywords: styrene-isoprene block-copolymers, waste polypropylene, melt blending

Abstract: Solid waste disposal is a significant to overhead in a shipyard environment. In many areas of Galati the disposal capacity is being reduced and the cost of disposal is continuing to climb. The study of the behaviour of bitumen mixtures is an old subject in the literature. Many specialists have been trying to replace the sand with recycled materials resulting from blasting ship parts. The main purpose of this study is obtaining a bitumen mixture with a good behaviour to long use. The grit is an abrasive blasting material (ABM), having an angular form, used in ship repair processes prior to the application of coatings. It is produced by the pulverization of molten steel, followed by a series of thermal and mechanical treatments in order to give the product its final characteristics. The shipyard in Galati generates annually thousands of tons of used blast grit and they dispose of it in landfills or directly into the Danube as a usual practice. We intend to find possibilities of disposing the wastes produced by shipyards, our research being focused on achieving the sustainable development requirements of the civil society. Environmentally speaking, recycling spent ABM has the potential to significantly reduce waste generation while saving money. Keywords: mix asphalt, grit, recycling, shipyard

Abstract: In the present study we evaluated the applicability of laser Doppler line scanning in recording the gingival healing process after a surgical procedure followed by two types of plastic provisional restoration. The laser Doppler imaging is a non-invasive method for analyzing the perfusion map of a certain area and can be used in order to establish the health status of a certain region after surgical treatment. The two types of plastic temporaries had no negative influence on the healing process. Key words: composite materials, laser Doppler imaging, microcirculation, non-invasive diagnosis, real time imaging

Abstract: Two compounds containing mesogenic cores based on dithiophene and dithienothiophene or fluorene units and hexyl end groups have been synthesized and their thermotropic properties were studied. The mesomorphic behaviour has been analyzed in the thermal stability range, by three complementary methods: polarized light microscopy, differential scanning calorymetry and variable temperature wide angle X ray diffraction. It was established that both compounds form a mesophase at low temperature, whose architecture depends by the mesogen molecular structure. By thermal treatment of the compounds in the mesophase stability range continuous ordered films have been obtained. Keywords: liquid crystal, internal plasticizer, ordered film

Abstract: Assuming that the “structural” elements of a multiphase fluid (hydrogel, drug or fluid particles) move on continuous and non-differentiable curves (fractal curves), a new theoretical model that describes the drug release processes from polymeric hydrogels is established. This model, namely fractal hydrodynamic model, is based on two equations: the momentum and probability density conservation laws. The fractal potential, from the momentum conservation law, is a measure of the non-differentiability of the movement curves and controls the drug release processes. The model allows us to evaluate some characteristics of the hydrogel network, such as a distribution parameter for drug particle inside hydrogel. The novelty of this approach is that the system complexity is replaced by fractality, eliminating thus the whole classical “arsenal” of quantities from the standard physics based on the assumption of continuity and differentiability of physical quantities (differentiable physics). Keywords: fractal hydrodynamic, drug release, polymer, hydrogel

Abstract: The carpet waste fibers and waste glass that create a serious environmental problem can be converted into useful products. The use of these waste materials in a cement-based composite can be a promising direction for waste reduction and resources conservation. In this study, several tests carried out to investigate the performance of control mortar using recycled glass and fibers as a fraction of aggregates in a cement-based composite. These tests included compressive strength, flexural strength, flexural toughness and water absorption. The results revealed that carpet waste fiber and waste glass could be reused as substitutes for conventional materials in cement-based composites. Keywords: Cement-based composite, carpet waste, waste glass, polypropylene fibers

Abstract: The objective of this study was to develop some new hybrid hosts based on dendrimers and montmorillonite designed for 5-Fluorouracil drug encapsulation. The presence of drug within the hosts was pointed out using different methods like FTIR Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), Thermogravimetric analysis (TGA), UV-Vis Spectroscopy and X-Ray Diffraction. The UV-Vis results showed that the dendrimer type involved in the hybrid hosts influenced the drug release. Keywords: antitumoral drug, dendrimer, montmorillonite, drug release system

Abstract: The thermo-mechanical behavior of silica-reinforced crosslinked elastomers has been examined by conducting shear thermorheological experiments and microstructural evaluation on two series of randomly crosslinked poly(dimethyl-siloxane) (PDMS). For all the samples studied here it was found that due to the featureless mechanical spectrum, the time temperature superposition (TTS) principle could not be applied to expand the accessible frequency range by the construction of master curves. Characterization of the filler particles before and after their inclusion into the PDMS matrix was conducted by dynamic light scattering (DLS) and transmission electron microscopy (TEM). These observations are discussed with respect to recent evidence that particle clustering may occur in non-crosslinked systems. Finally, short time high temperature aging (up to 30 hrs) experiments were observed not to influence the viscoelastic behaviour. Keywords: highly crosslinked siloxane elastomers, linear viscoelasticity, time-temperature superposition, silica filler

Abstract: The increasingly wider scale use of various foreign materials in Orthopaedics and Traumatology require long-term study of their interaction with adjacent bone, with soft tissue, and also the integration of these materials into the bone tissue. One of the likely consequences of using implants and metal fasteners is the production of conductance disturbances of bone which are dependent on the type of material used, with major implications for its biology and by default on fracture healing. The purpose of this paper is to highlight the changes in focal bone fracture biopotentials depending on the chemical composition of biomaterials used. The study is experimental, on a group of 23 Wistar rats which were created femur bone defects that were repaired by autotransplantation of the hip bone with different wire set. The potential difference between the graft and the graft bed was measured and was correlated with the chemical composition of biomaterial. The largest potential differences were reported with aluminium wire, copper, and nickelin wire, while V4A wire (alloy of nickel, chromium and titanium) determined the smallest disturbance of these biopotentials. Keywords: biopotentials, aluminium, copper, V4A, bone callus

Abstract: Multitude of methods for the synthesis of nanoparticles express interest and importance of this field. In the present study, are addressed the aspects of obtaining nanoparticles by milling, in order to be used at nanostructured coatings in asphalt. Materials used for obtaining nanoparticles were powdery volcanic tuff with 0.4-1.6 mm grain and calcium carbonate. Stearic acid, sodium lauryl ether sulphate, a mixture of fatty acid imidazoline, a block copolymer polyethylene oxide- polipropilenoxid -polyethylene oxide and polyethylene glycol were used as additives. For grinding of inorganic particles was used a laboratory planetary mill Fritsch Pulverisette 6, equipped with a stainless steel grinding bowl. Grinding dry powdered volcanic tuff in the presence of additives influences particle size distribution. Wet milling of powdered volcanic tuff in the presence of ROT favours getting a bimodal distribution and decreasing the average particle size. Keywords: nanoparticles, grinding, additives, particle size distribution

Abstract: Applications of digital image correlation (DIC) method to material characterisation has been proven to be a powerful tool for deformations and strain analysis and found widespread use and acceptance in the field of experimental mechanics. This paper describes the potential, accuracy and limitations of a commercial DIC system to full-field, real-time characterisation of the coefficient of thermal expansion (CTE) of polymeric materials. The topics such as strain calculation procedure and influence of a small rigid body rotation were theoretically described and experimentally verified. A series of measurements was carried out to determine the CTE polypropylene (PP) and polyvinylchloride (PVC) commercial plastics. To check the feasibility of the method an aluminium sample was initially analysed. The measuring set-up developed includes a simple heating device, thermal sensors and a thermo-camera for real-time temperature measurement and monitoring of the sample and a 3D-DIC measuring system. The results revealed that the DIC can be a reliable tool for thermal deformations measurement especially suitable for polymeric materials with a higher CTE. Keywords: digital image correlation, thermal strains, polymeric materials

Abstract: Photosensitive polymers based on polysiloxanes substituted with different azo and quaternary ammonium groups were synthesized and characterized. The chemical structure of the synthesized polymers was confirmed using 1H-NMR spectroscopy. The photochromic behaviour was evaluated as a result of the interaction with UV light. The micellar aggregation/disaggregation capacity of the polymers was investigated using fluorescence spectroscopy and dynamic light scattering techniques. All the synthesized amphiphilic polymers are able to generate micelles, the critical concentration of aggregation values being situated in the domain (3-13) x 10-3 g/L. The morphology of the micellar aggregates is fundamentally influenced by the polymer chemical structure. If in the case of azobenzene and azo-5-crwon-15-ether groups it is possible to obtain 35-155 nm diameter individual micelles, for the azo-6-crown-18-ether group, only small aggregates with diameters below 10 nm can be obtained. The micelle’s disaggregation capacity as a consequence of UV irradiation is strongly affected by the hydrophilic/hydrophobic ratio, as well as the chemical structure of the azo groups. Keywords: azobenzene, polysiloxane, photosensitive micelles