Volume 51, Issue 2

Abstract: Novel composite poly(ethylene glycol) hydrogels with hydrophilic bentonite as the filler were synthesized by the polyaddition reaction between diepoxy-terminated PEG of 2000 Da, 6000 Da and 10000 Da molecular weights and ethylenediamine in aqueous solution at 60°C, in the presence of the clay. The hydrogels prepared were tested from the point of view of their swelling behaviour and mechanical properties. The results showed that the clay practically did not affect both the water absorption by the crosslinked polymer and the storage modulus of the hydrogels. This seems to indicate that the interactions between the PEG chains and bentonite were very small or absent within the hydrogels in the presence of water, although they occurred in dry state, as proven by FTIR and XRD measurements upon xerogels. Keywords: hydrogels; poly(ethylene glycol); bentonite; composite

Abstract: The paper focuses on the synthesis and evaluation of biomineralization potential of composite materials based on bacterial cellulose and synthetic acrylic polymers with negative groups attached. The composite materials were obtained by grafting the monomers carrying negative groups onto the surface of bacterial cellulose. These grafted membranes were then subject to mineralization assay according to T. Kokubo protocol. Cytototoxicity test have shown that this kind of composites did not show a significant in vitro cytotoxicity and could be used for developing biomedical applications. Keywords: bacterial cellulose, acrylic monomers, biomineralization, hydroxyapatite

Abstract: New systems based on poly(vinyl alcohol), unmodified and modified layered silicates were designed for drug delivery applications. Unmodified and modified montmorillonite with different agents were used as inorganic component in the hybrid structures. The thermogravimetric analysis (TGA), X-Ray Photoelectron Spectroscopy (XPS), X-Ray Diffractions (XRD) and FTIR analysis were useful to characterize the hybrid materials. The modifier agent type used for montmorillonite treatment and the presence of montmorillonite in the polymeric films strongly influence the hybrid materials properties and drug release profile. Keywords: poly(vinyl alcohol), hybrid materials, montmorillonite, 5-fluorouracil, UV-Vis, X-Ray Photoelectron Spectroscopy

Abstract: The paper presents experimental data regarding morphology and hydrophobic character of some film building silica hybrids containing disperse dyes embedded or covalently linked into the inorganic network, used as coating materials for protein textile fibers. Thermo-mechanical properties of the textiles coated with the colored film forming materials are studied in relation with the coating materials composition. Keywords: thermo-mechanical properties, hydrophobic character, silica hybrids, disperse dyes,protein fibers

Abstract: This paper has had as purpose rendering of some researches related to extrusion velocities while obtaining multilayer films with superior barrier and antimicrobial properties, of five layers of polymer with ionomer content, including antimicrobial. An installation comprising five extruders has been used for trials and the working velocities have been determined for each layer, as well as the shear stress at the wall of the nozzle. The results thus obtained made possible to settle the optimum parameters for the extrusion process able to ensure a stable flow of the molten polymer, which resulted in a uniform multilayer, faultless structural film, with superior barrier and antimicrobial effects. Keywords: polyethylene, EVA, EVOH, extrusion, co-extrusion, multilayer film

Abstract: This paper presents the study of Vickers microhardness performed on a styrene-butyl methacrylate- methylacrylic acid copolymer and the analogous obtained by grafting with ampicilline. The creep properties and the glass transition temperature of the copolymers were investigated. Keywords: microhardness, styrene-butyl methacrylate-methylacrylic acid copolymer, creep,Tg

Abstract: A simple manufacturing method to obtain bent shape tubes with variable cross-section from fibre reinforced composites with application in high performance handlebars for mountain-bicycles was used. The original procedure is able to assure constant pressure upon the reinforcement material, the result being a compact composite, good quality with an optimum reinforcement degree. Tests and analytical computations, based on classical laminated plate theory delivered the engineering constants that have been used in the finite element simulations of two important safety tests for the handlebar (bending and torsion). The experimental results obtained for lateral bending test (critical test) are in agreement with the finite element simulations. Keywords: bicycle handlebar, composite parts, mechanical testing, finite element simulation

Abstract: The paper deals with the research of variety of non-standard samples of plastic material made by injection moulding. The samples were made of conductive plastic material (LNP Stat-kon Compound ZX05009). Brown Corundum F24 was used for blasting under different pressures. This conductive plastic material can be applied as a plastic electrode, it is therefore possible to make measurements and examination of electrical conductivity. The experiment is used in order to establish the extent, to which the pressure used at blasting measurably affects the electrical conductivity of plastic electrode. Keywords: physico-mechanical properties, casting, plastic electrode, injection holding

Abstract: The objective of this work was the modification of the pigment Yellow 17 structure through a treatment with ZnCl2 and Na2SiO3 in order to improve its properties. The modifications that appear in pigment structure were revealed by UV-visible diffuse reflectance and EDX analysis. The synthesized pigments were used to colour the polypropylene. The chromatic modifications appeared through pigment colouring with modified pigments were evaluated by measuring the colour intensity and colour difference. The light fastness and UV protection of the coloured polypropylene samples were also highlighted. Keywords: organic pigments, polypropylene, colour measurements, light fastness, UV-protection

Abstract: The present paper aims to investigate the effect of surface defects upon contact area shape and dimensions in the case of metallic spherical punches pressed against a flat, optically transparent surface. Experimental investigations were conducted using a previously advanced, optical method, based on surface reflectivity. Various surface defects were artificially generated on the surface of steel ball bearing balls with 12.775 mm in diameter. The considered defects were grooves and holes. The employed experimental method is based on the accurate evaluation of contact interface reflectivity of loaded contacts, by aid of laser profilometry, as described in previous works [1-9]. Keywords: surface defects, mechanical contacts, contact area, laser profilometry, reflectivity

Abstract: The aim of this study was to investigate the surface topography and to compare the calcium and phosphorus ions concentration in dentine and cement following their contact with five acidic drinks in the presence or absence of saliva. 25 caries free extracted teeth were used in this study. All the teeth were longitudinally sectioned in three slices. One slice has been stored in distilled water (control group). The second slice has been continuously immersed for 12 h in one of the tested beverages: Red Bull, Lipton Green Tea, a commercial apple juice, a natural carbonated mineral water and lemon juice. The third slice has been subject to 3 cycles of immersion in one of the tested beverages for 1 min, followed by storage in artificial saliva (AFNOR NF S90-701) for 4 h. The samples were analyzed using a scanning electron microscope and an EDX detector. The specimens continuously stored in acidic beverages showed enlarged dentinal tubules. The specimens successively stored in acidic beverages and saliva showed a slightly eroded surface of dentine and cement. The calcium and phosphorus ions concentration in dentine and cement significantly decreased following continuous storage in all the tested beverages (mean calcium ion concentration (wt%) in dentine (D)/cement (C): 28.17/23.93 control group, 16.45/11.07 apple juice, 22.84/11.48 Lipton Green Tea, 24.01/21.46 natural carbonated mineral water, 15.06/9.22 lemon juice, 18.09/10.52 Red Bull; mean phosphorus ion concentration (wt%) in D/C: 10.80/ 9.92 control group, 7.84/6.55 apple juice, 8.70/6.98 Lipton Green Tea, 9.39/9.21 natural carbonated mineral water, 7.45/6.28 lemon juice, 7.85/6.79 Red Bull). The decrease of mineral ions concentrations in dentine and cement was significantly lower when saliva has been used as a storage medium between immersions in acidic beverages (p < 0.05, ANOVA and Bonferroni test). Under the conditions of this study, saliva offered to dentine and cement a protective effect against the acidic challenge of tested beverages. Keywords: dentine, cement, acidic beverages, SEM, calcium ions, phosphorus ions

Abstract: The aim of our study was to obtain cellulose acetate composites based on hydroxyapatite and nystatin with increased local therapeutic effect in the therapy of candidiasis. The porous composites were obtained by phase inversion method. Antifungal susceptibility of the samples was investigated by the Kirby Bauer Disk Diffusion test. The method has demonstrated an antifungal effect of the samples against Candida albicans as well as the fact that the polyene antibiotic nystatin might be an optimal choice as active agent incorporated in a composite. Also we have studied the swelling and the degradation of the membranes. These measurements help us better understand the water and PBS absorption capacity of the polymer matrix. Keywords: Composite, cellulose acetate, hydroxyapatite, nystatin, antifungal activity

Abstract: This paper presents the results of the author’s latest researches on lignocellulosic basic structure composites, which resort to wood fibres and chips, in admixture with mineral binders - cement and gypsum. The obtained products, shaped as boards and blocks, may be deemed “ecological products” with applicability in the field of Civil Engineering, both as plating materials and as filling material (for the sandwich-type structures). The obtained results may be reckoned for the theoretical and experimental basis for further development of the materials and products achievable in industrial systems and usable in the structure of constructions for various purposes. Keywords: composites, wood chips, wood fibres, adhesiveness, embedding

Abstract: The research highlights the main trends and guidance in the design of products using plastics in conditions of sustainable development of society. Plastics have an important role in the configuration of the new products still in the phase of conception. Having in view the main advantages of the utilization of plastics the expectation is to see an increase of the weighting of these ones in the products development. The present work spotlights the positive influence of the covering of the alloys with polyester. Especially it aims to increase the wearing resistance and resistance to fragility that has a direct effect on the increase of the functioning time in the total life cycle of the product. Keywords: polyester graphite, wear resistance

Abstract: In the industry of plastics and dyes, pharmaceuticals and agriculture, the toxic effects of heavy metals have been reported during prolonged professional exposure. Heavy metals in the environment can enter the body orally, inhaled or by skin absorption. Unlike other toxins present in the environment, heavy metals accumulate in tissues because the body has no ability to remove them. Heavy metals in excess cause numerous metabolic imbalances. In cancer, heavy metal overload could be a stimulus for secretion of chemokines, for promoting oxidative stress and antioxidants inactivation, for altering cell signaling, for promotion and progression of tumorigenesis. Strategies to prevent accumulation of toxic metals, to decipher the pathophysiological mechanisms by which heavy metals affect cell metabolism, to increase excretion of toxic metals without removing essential minerals in the body is the subject of current researches. Keywords: heavy metals, dyes, plastics, skin cancer

Abstract: Poly(ethylene terephthalate) PET was subject to a glycolysis process using diethylene glycol (PET/DEG = 1/1 molar ratio) and zinc acetate as trans-esterification catalyst. An unsaturated polyester resin was then prepared using the glycolysis product and maleic anhydride. The molecular weights of glycolysed PET products and polyester resin were investigated using gel permeation chromatography (GPC) analysis. A cross-linking reaction of the unsaturated polyester resin was performed in the presence of styrene (different amounts) at 80°C. The compression and impact strength/resistance properties of the cured resins were determined. Keywords: PET waste, glycolysis, GPC, unsaturated polyester resin, mechanical properties

Abstract: The J integral method was used to characterize the dependence of stresses and strains in the vicinity of the crack tip in thermoplastic materials with nonlinear deformations. This method makes it possible to establish the correlation between crack growth resistance of the material based on the stable propagation and the crack extension by means of J-R curve, which is an indicator related to the toughness of the material. The paper presents the results of experimental researches carried out on three-point bending test specimens of thermoplastic high density polyethylene - type PE 100, taken from the pipes with 110 mm diameter. Keywords: J-integral, J-R curve, toughness, thermoplastic materials, polyethylene PE 100

Abstract: An incompressible MHD flow of two-dimensional upper-convected Maxwell fluid over a porous stretching plate with suction is studied. The nonlinear differential equation is solved approximately by means of the Optimal Homotopy Asymptotic Method (OHAM). Multiple solutions are given, showing a very good agreement between the analytical and numerical solutions. This procedure is very efficient in practice, ensuring a very rapid convergence of the solutions after only one iteration. Keywords: Maxwell fluid, porous stretching plate, optimal homotopy asymptotic method

Abstract: One of the biggest dangers to our environment today is the increasing number of unused synthetic rubber in the environment and these pose a big threat to nature, if it is not disposed properly. Typically, synthetic rubber is developed for specific applications, and is specifically for those applications due to the process used to make them, and the resulting properties. Dumping these synthetic rubber in dumpsites could contaminate nearby water sources. Heating these synthetic rubber with normal heat will generate harmful chemical substances, like carbon and lead, which are really dangerous for humans. Dealing with rubber properly is not only advantageous to nature, but also to humans. Recycling represents a best alternative to the disposal of post-consumer rubber in common landfills if it is possible to obtain new materials with good final properties compatible with practical application. In this study, characterization and properties of virgin acrylonitrile butadiene rubber/recycle acrylonitrile butadiene rubber (vNBR/rNBR) were examined. Three different size ranges of rNBR particles, i.e., 150 - 350 mm, 2.0 -15.0 mm, and 5 -10 cm were used in this study. The vNBR/rNBR blends with blend ratios of 95/5, 85/15, 75/25, 65/35, and 50/50 phr (part per hundred rubber) were prepared using a two roll-mill at room temperature. The vNBR/rNBR blends with smallest size of rNBR particles show better tensile properties (tensile, elongation-at-break and M100) compared with all other blend ratios. For physical properties, vNBR/rNBR blends with smallest size of rNBR particles exhibited the highest hardness and cross-linking density at all blend ratios whereas resilience decreased, accordingly. The cross-linking density of vNBR/rNBR blends also show an increasing trend with increasing rNBR content. A morphological study of tensile fracture surface of the blends was also carried out. The scanning electron microscopy study indicates that rNBR exhibited a weak rNBR-vNBR matrix interaction particularly when more than 25 phr of rNBR was used, thus decreasing the mechanical properties of vNBR/rNBR blends. Keywords: vNBR, rNBR, Curing characteristic, Mechanical properties, Morphological properties

Abstract: For determining the optimal conditions of the cutting process (material and tool geometry, process parameters), quantitative data are necessary concerning the roughness of surfaces. Using experimental research methods, this work aims at determining equations between surface roughness and parameters of the milling, process for some polyamides samples (PA66, PA66 – GF30 and PA66 MoS2). PA66, PA66 – GF30 and PA66 MoS2 polyamides are technical thermoplastics with excellent mechanical and physical properties, increasingly used in industrial machinery. Keywords: surface roughness, milling, polyamides

Abstract: The maxillo-facial reconstructive surgery very often uses regular shape biocompatible material plates which are fastened by screws to the rest of the bone. The choice of optimal plate for each case, especially in risk cases, should be made primarily according to surgeon medical experience but also following a strength analysis of the various existing plates. The analysis of mechanical structures by using the finite element method highlights the resistance, the risky areas in case of possible demands such as the jaw’s pressure on the mandible, allowing the physician to optimize the restorative solution. Keywords: finite element, osteosynthesis

Abstract: The choice of denture artificial teeth is made up onto several criteria regarding both aesthetics and functionality. Of these, colour stability is one of the determining factors. Colour stability of materials used in aesthetic prosthetic restoration is important for the long-term success of the treatment. Our study was conducted to compare colour stability of different acrylic artificial teeth available on the market and usually used in manufacturing partial and full dentures in Romania and to find a ranking of staining ability of different solutions with which artificial teeth could come into contact lately, during function or cleaning phases. For this study were purchased six boxes of identical front superior acrylic denture teeth from four different manufacturers, coded by letters V, M, R and S). These teeth were immersed in various liquids such as red wine, Coca Cola, black tea, coffee, which we considered to be ingested frequently by the largest part of the population. Our study shows that, of the four analyzed drinks, the most colouring is coffee. The same operator determined the color coordinates using the Easy-Shade intraoral spectrophotometer. The results were expressed using CIELAB colour notation system. Color difference was expressed as DE*. A device was made for constant positioning the tooth versus the Vita Easy Shade spectrophotometer rod used to determine colour changes in the central third of the buccal area. The acrylic prefabricated teeth suffered various colour changes in contact with those drinks, with magnitudes depending on the type of the liquid and the acrylic teeth chosen. We compared colour stability of two batches of homolog teeth, first unmodified and second grinded and polished in the dental laboratory, from which the most affected were R and M where this colour change occurs in three of the four kinds of drinks in which we have made the immersion. Washing the dentures with soap and water reduced differences in colour caused by contact with any type of these drinks. Keywords: color stability, denture, acrylic teeth, staining drink

Abstract: Longevity of fixed partial dentures fiber-reinforced composite restorations is dependent upon many different factors, including material, maxillary or mandibular arches, patient- and dentist-related. 25 metal polymeric and 25 integral polymeric fixed partial prosthesis were obtained for this study. The Rx investigation was performed by using the Fona X 70. The possible defects were investigated with the DIAGNOcam using the transillumination method. In contrast to conventional technology with an interdental light source, DIAGNOcam practically uses the entire tooth as a light propagation medium. the transillumination investigation detects more defects trapped in the polymeric materials in 20 from the 25 metal ceramic fixed partial prosthesis and in 16 from the considered 25 integral polymeric fixed partial prosthesis. In conclusion, a noninvasive evaluations method, such as transillumination, has a great capability to evaluate the internal structure of the polymeric material used for the fixed partial prosthesis considered. Most of these defects were identified in the occlusal, cervical and connector’s areas of the fixed partial prosthesis and then could lead to fractures and failures of the prosthetic treatment. Keywords: polymeric fixed partial prosthesis, transillumination, non-invasive method, material defect