Volume 58, Issue 1

Abstract: Theobromine (Th) was documented during the last decades for its important role in the prevention of dental caries, having this role dueto its antibacterial action against the Streptococcus mutants and S. sanguinis, thus reducing the formation of dental biofilm on the teeth surface. Thermally induced interactions of theobromine in 1:1 mass ration bynary mixture with different types of Poly(methyl methacrylate) based materials and the induced interactions between Poly(methyl metha-crylate) based materials and HA were performed using thermal analysis and FTIR spectroscopy. This study aims to be a preliminary study for various mixtures of HA/methacrylate-based materials and Th with usage in dental applications. The instrumental techniques used can be successfully applied in the characterization of dental materials and can lead to conclusions on how to use them.Studies have led to the conclusion that Th can be used for the treatment of early decay by incorporation into the polymer material. It is recommended to use these materials as successive layers (Th with HA and after that dental material).

Abstract: By the extrusion and injection technique, polymer-based composite samples (polypropylene and thermoplastic polyurethane) were obtained with BaTiO3 filler in concentrations between 0 and 35 %. Following the preliminary characterizations performed by coupled thermal analysis techniques, it was found that the composite samples obtained have thermal stability up to a temperature of about 250 oC and can be processed by extrusion at temperatures between 180 and 240oC. Above this temperature, a series of degradation processes take place by successive thermooxidation with the formation of volatile products.The electrical characterization of the composite samples was performed by the dielectric spectroscopy technique, which showed that the Ätgä dielectric losses increase as the BaTiO3 content of the composite increases. The maximum increase being recorded at 50 Hz (the slope Ätgä /% BaTiO3 about 0.003 /% BaTiO3). It was also found, that the electrical conductivity (ó) of the composite increases with the increase of content in BaTiO3 so that ó at 100 kHz for the composite with 35 % BaTiO3 is about 50 times higher than for the reference sample M 0 (without filler).

Abstract: The present paper reported the obtaining of an environmental friendly adsorbent based on sodium alginate, chitosan and glass bubbles. CaCl2 was used as crosslinking agent for sodium alginate favoring the interactions by physical bonds between the negative groups (-COO) of biopolymer and the Ca ions. The experimental study to determine the Cu(II) uptake using an atomic absorption spectrometer was conducted in the testing stand at the 1:50 and 1:100 ratios between the adsorbent mass and the amount of pollutant in solution. The number of cycles of regeneration of the adsorbent material was also evaluated. The characterization of alginate/chitosan/glass bubbles adsorbent by scanning electron microscopy (SEM) coupled with energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FTIR) showed that the Cu(II) was found out on the surface of adsorbent.

Abstract: Knowing how to deform the Turcite thermoplastic material under the action of conical penetrators is a means of obtaining information on the processing of the counterpart (made from a metal material with higher hardness) with which it comes into contact.The paper aims to theoretically determine the depth of penetration of the thermoplastic material under the action of some conical penetrators and to establish the coefficient of static and kinetic friction under the action of these penetrators. The proposed model will be validated experimentally on a tribological stand made for this purpose.

Abstract: The effect of Crosslink density on Cut and Chip resistance was affected on a typical 100 percent styrene-butadiene rubber (SBR)-based tire tread compound. In order to successfully develop products for tires used in off-road or poor roads and other demanding rubber applications, it is important to understand the C&C effect in rubber. Crosslink density varied by varying the sulphur to the accelerator ratio and also by changing the process aids. Basic polymer, filler and other ingredients such as activators and anti-degradants have remained unchanged. In the first setup, the sulphur was kept constant and the accelerator varied and the reverse was done in the second setup. It was made to achieve different crosslink density by changing the oil dosage and adding different resins. An attempt has been made to correlate Cut and Chip resistance to other physical properties. All these tests have been identified and optimized by the traditional tire tread compound.

Abstract: The chemical composition of a hybrid resin made of natural Dammar resin and epoxy resin (along with the related hardener), in proportion of volume of 60 and 40%, respectively, was studied based on EDS analysis. The results of the study are presented in this paper. The presence of epoxy resin was necessary to generate a rapid polymerization process. The material details of the hybrid resin were investigated using SEM. A high-resolution image of a hybrid resin sample was obtained. The weight loss of the hybrid resin at certain temperature values using thermo gravimetric analysis was measured. In addition, the surface roughness of the hybrid resin was characterized using two methods. By the first method, the classical one, the roughness was measured using two profile parameters and five analysis lines, namely the functional dependence between the roughness height and the gray level of the analyzed surface image. By the second method, the average roughness method, the surface texture of a hybrid resin specimen was measured and the roughness profile was obtained as the difference between the primary profile and the middle line of the filter determined with the Gaussian profile filter. Finally, several possible areas of use of this type of resin have been proposed based on the properties obtained.

Abstract: In this work, biodegradable Poly(L-lactide) (PLLA) was modified through adding a new organic additive N, N`-bis(benzoyl) 1, 4-naphthalenedicarboxylic acid dihydrazide (NABH). A comparison on crystallization of the pure PLLA and PLLA/NABH revealed that the NABH as effective heterogeneous nucleation sites enhanced PLLA𠏋 crystallization, and an increase of NABH loading was able to further accelerate crystallization rate of PLLA; whereas a faster cooling rate was not conducive to PLLA𠏋 crystallization, but the appearance of obvious crystallization peak upon cooling at 30ºC/min confirmed the advanced enhancing role of NABH for PLLA crystallization again. The investigation on influence of the final melting temperature on the crystallization behavior of PLLA showed that the 170 ºC was optimum final melting temperature for enhancing crystallization, even the onset crystallization temperature of PLLA/NABH were higher than 150ºC. The melting processes of PLLA/NABH after different crystallization not only could reflect the previous crystallization, but also depended on crystallization temperature and heating rate. Thermal decomposition results showed that the existence of NABH slightly weakened thermal stability of PLLA, and the maximum difference in onset thermal decomposition temperature was only 9.4ºC comparing with the pure PLLA. However, the presence of NABH in PLLA matrix seriously weakened optical property.

Abstract: This work is devoted to the preparation and characterization of some polystyrene/multiwall carbon nanotubes (PS/MCNT) systems. The dispersion of the reinforcement agent within the PS medium was done via sonication and the resulting nanocomposites containing 0-40 wt% MCNTs were achieved by solution blending procedure. Shear flow and viscoelastic properties were tested by means of rheology, revealing some changes in the sample microstructure. Dispersion curves of the matrix and low filled nanocomposite were registered at variable temperatures. The theoretical refractive index and corresponding dielectric constant at optical frequencies were analyzed as a function of the system composition. Heat transport in the reinforced materials was examined by computer modeling, which enabled calculation of thermal conductivity. Electrical transport features were assessed using a theoretical approach relying on the physical properties of each phase. The surface adhesion of the samples with various materials was determined to check the suitability for applications in technical or bio-related fields.

Abstract: In the presented study, the load induced long-term behavior of a biocomposite material is analyzed. The studied material is a unidirectional flax fiber reinforced epoxy resin, material, whose quasi-static mechanical properties can compare with those of glass fiber composites. Samples with a fiber direction of 0° were subjected to two types of multi-level creep-recovery tests, one with a varying creep duration, and the other with a varying creep stress, with the purpose of discriminating the viscoplastic and viscoelastic behavior of the composite. Results show a significant viscous response in time, dependent on both creep duration and creep stress, up to 20% of the elastic one. Sample damage is absent, leading to the conclusion that the viscoplastic response is caused by the permanent reorganization of the fiber’s internal structure.

Abstract: This aim of this paper is to perform a study on the way the material of the fittings that can be welded through eletrofusion on polyethylene pipes withstands. The process is observed by means of the thermal and fast cameras. Also we intend to analyze the way the assembly consisting of the polyethylene fitting and pipe behaves during welding. The stresses caused by the welding process are observed, as well as the concurrent welding of the tapping tee and the branch saddle tee.

Abstract: Heat cured polymethylmethacrylate (PMMA) has been used as denture bases since 1937. PMMA is a vinyl polymer, made by free radical vinyl polymerization from the monomer methyl methacrylate [1]. After the success of using as prosthetic material in the mouth, PMMA began to be used in other areas, for example in facial prosthetics, for facial epitheses. The facial epitheses are exposed permanently to ambiental changes (temperature, air currents, humidity). Secondary, for a better esthetic effect, in facial epitheses PMMA often contain variables quantities of natural fibers (cotton, wool). Our study has analyzed how a PMMA facial epithesis reacts to temperature changes during heat exposure in the summer, especially depending on the amount of fiber it contains, considering that the biological interface between the prosthesis and facial tissues is sensitive to heat [2].

Abstract: Nowadays, the investigation of both classic and new materials for blast mitigation applications is a subject intensively approached in the scientific literature. Due to their mechanical behavior, the polyurethane foams are materials with high potential for this type of applications. Within the current paper a EUROPLASTIC® polyurethane foam grade mixed with fly ash ceramic micro powder was experimentally investigated. Using a single stage gas gun, the dynamic response of polyurethane/fly ash ceramic foam was thoroughly evaluated in terms of specific stress vs volumetric strain curves response and dissipated kinetic energy, also.

Abstract: The paper presents the structural and dimensional differences of rectangular shape samples manufactured by selective laser sintering (SLS) according to three process sinterization energies. In this study we determine the geometrical and structural characteristics of biocompatible PA2200 polyamide manufactured at a low energy density E1, and intermediate value E2 and a high energy density E3. Relaying on these results, four custom-made medical parts have been built using biocompatible polyamide PA2200 powder, in order to evaluate their performances.

Abstract: Cranioplasty is a surgical procedure that is used to correct any defect in skull bones after a previous decompresive craniectomy, usually made for traumatic brain injuries, with ischemic or hemorragic nature, or after a tumor removal. A composite for modeling on a defect in skull bones was prepared by crosslinking poly(methyl methacrylate) in the presence of barium sulfate. The crosslinking rate of methyl polymethacrylate in the presence of the benzoyl peroxide initiator, the N, N-dimethyl-β-toluidine polymerization accelerator and the hydroquinone polymerization inhibitor allows modeling according to the location and size of the defect. Thus, the concentration of composite precursor components was optimal for this purpose. The TGA diagram shows the almost total consumption of methyl methacrylate and butyl methacrylate monomers in the crosslinking process of methyl polymethacrylate with the formation of the composite. This technical study demonstrate the efficacy of this treatment, as well as to show all the possible scenarios in such procedures.

Abstract: The present paper was focused on studying the influence of shelf life of an epoxy matrix on the mechanical properties of glass fibre reinforced composites. For the study, two types of the same epoxy system were used, one during its shelf life and one out of its shelf life. The reinforcement used consisted in E-glass fibre fabric. Mechanical investigations were realized in order to compare the materials in terms of loss of mechanical strength and elastic properties. Therefore, three mechanical tests were performed: tensile tests, in-plane shear and open-hole tensile tests. The results showed that the shelf life affects the mechanical properties of the polymeric composite. A decrease of 24% in tensile strength was recorded along with a 28% decrease of the in-plane shear strength and 55% of open-hole tensile strength for the composite manufactured with the out of shelf life epoxy system compared with the other composite. An overall reduction of mechanical strength and elastic properties of the composite material was observed, primarily due to polymeric matrix degradation, which after long periods it could be prone to brittleness and susceptible to delamination and fracture. The thermogravimetric analysis showed that thermal induced changes are happening at a higher speed in the out of shelf life composite, a lower mass loss being registered for new epoxy composite.

Abstract: In order to improve thermal behavior and dimensional strability of polylactic acid (PLA) designed both for 3D and 4D printing technology-fused deposition modeling (FDM) using a scalable procedure, the polymer was melt compounded with additives which control the morphology by crystallization and/or reinforcing. Using the formulations which provide polylactic acid (PLA) improved thermo-mechanical properties and desired dimensional stability, the new materials were shaped, on a laboratory line, as filaments for printing technology. The selected compounds were than scaled up on a 50 kg/h compounding line into granules which prove to have good shapability as filaments for printing technology (1.85 +/- 0.05 mm diameter, required ovality, good appearance and smooth surface) and performed properly at 3D printing. The obtained results proved that functional properties of PLA can be improved by various methods so that, depending on the reached performances, the new material can be converted through printing technology into items for performance applications. The novelty of the article is related to the fact that it identifies a modifying solution for controlling the morphology of a type of PLA designed for 3D printing that already has an advanced crystallinity.

Abstract: Wastewater containing Cu (II) ions has become a huge environmental problem worldwide because ingestion of copper ions affects the human body leading to epigastric pain, nausea, vomiting, diarrhea and even death. The researches for new methods of treatment of wastewater polluted with heavy metals more efficient than the conventional ones led us to study Fe3O4 and his corresponding hybrid Fe3O4 –PVP as potential adsorbent nanomaterials for the removal of copper ions from industrial wastewater. First, the two nanomaterials were synthesized by precipitation method and characterized by XRD, FTIR and TEM analyses. Then, the two obtained nanomaterials were tested within the process of copper ions removal from wastewater and factors influencing the process including pH and contact time were investigated. The maximum wastewater treatment capacity reached up to 97 % under the optimal condition using Fe3O4 and 70% for Fe3O4 –PVP.

Abstract: Graphene is a microstructure of graphite that has enormous properties and is also one of the carbon allotropes. There are several metals with low strength. The properties of these metals can be increased by coating the graphene. The primary goal of the work is to create composite graphene that exhibits the optimised properties and characteristics that meet the requirements of the industries. The properties of graphene when coated with other metals are studied and their applications in different industrial fields are analysed through several tests and experiments. Research-based on graphene coatings and composites is studied and the properties are adapted.

Abstract: Recently, 3D-printed polymeric materials have been successfully replacing the usual ones especially used in sliding systems like couplings. Among the polymeric materials, Acrylonitrile Butadiene Styrene (ABS) and Poly Lactic Acid (PLA) can be the competitive materials in such application after 3D-printing. In this study, 3D printing was used to produce samples from ABS and PLA via fused deposition modelling (FDM) technology. Then friction behavior of 3D-printed samples was investigated depending on printing orientation of the samples. Ultra High Molecular Polyethylene Weight (UHMWPE), as a well-known industrial polymer, was also used for comparing the friction behavior of 3D-printed ABS and PLA polymers. Friction tests were conducted using a pin-on-plate type tribometer according to ASTM G133 under different applied loads and sliding speeds at room temperature. It was found that printing orientation of all ABS and PLA samples has a considerable effect on their friction behavior. Transverse direction (T.D) of the 3D-printed samples shows higher coefficient of friction (COF) values than the longitudinal direction under all applied loads and sliding speeds. On the other hand, COF values obtained in both 3D-printed samples increase as the load and speed increase regardless of the printing direction. When both 3D-printed materials are compared, PLA samples exhibit lower COF values than ABS samples in both printing directions and under all loads and speeds. However, the UHMWPE sample produced with traditional method shows much lower COF values and stable change in friction behavior under all conditions compared to 3D-printed PLA and ABS samples.

Abstract: Due to the continuous decrease in the level of oil resource, nowadays researchers from all fields are concerned with the creation of new bio plastics with special properties. The present work presents a series of such properties, which become achievable when reinforcing organic fibre materials obtained by reactive extrusion of thermoplastic Polyurethan (TPU) with Polylactid-Acid (PLA) in a twin-screw extruder and covalently linked into PLA-TPU-Blends, through the innovative `one-step process` technology, using the IMC Krauss Maffei injection moulding compounder, at the IKT University of Stuttgart. The elongation at break of PLA-TPU-Blends and the impact strength could be increased without significant reduction of strength and stiffness. A balanced relation between improved impact strength and reduced stiffness can be achieved by varying of the blend components. By using the partially biobased Polyurethane and natural fibres, a biobased content of more than 90% could be achieved. More and more advanced technologies allow the manufacture of components with reinforcements made of glass fibres, natural or carbon fibres obtained from polypropylene or Lignin. Due to their low specific weight compared to glass, carbon fibres are preferred for lightweight structures in the automotive or aeronautics industries. Green Carbon fibres, made in innovative ways from acrylonitrile resulting in the production of Bio-Diesel from algae, can successfully replace the conventional carbon fibres of Polypropylene, having identical properties. Fibre reinforcement aims to improve mechanical strength and impact resistance and increases the dimensional stability under heat of the composite. This feasibility study shows a method to realize fibre-reinforced materials using Green Carbon fibres with remarkable stability and rigidity similar or better than aluminum and steel for lightweight constructions.

Abstract: In this work, the corrosion resistance of hybrid coatings obtained from plastic materials was evaluated and compared with the corrosion resistance of Zn coatings. Zinc and hybrid coatings were obtained by electrodeposition from zinc sulphate electrolyte. For obtained hybrid coatings it was used as disperse phase two type of plastic materials: phenol-formaldehyde resin and epoxy resin. Polarization was used to measure the corrosion rate and behaviour of zinc and hybrid coatings in 3.5% NaCl solution. Tafel curves show that the including particles of plastic materials in zinc matrix disturbs the cathodic reactions and reduces anodic reaction leading to decrease of corrosion current and increase the corrosion resistance of hybrid coatings obtained at the same electrodeposition parameters as zinc coatings. Smallest values of corrosion rate were evaluated for hybrid coatings obtained with phenol-formaldehyde resin as disperse phase that indicates a good corrosion resistance in 3.5% NaCl solution.

Abstract: The current study was proposed in order to obtain, to characterize by usually physico-chemical methods and to assess in vitro, the potential cytotoxic effect of polyurethane microstructures loaded with epigallocatechin gallate (PU_MS) on human pharyngeal carcinoma cells (Detroit 562) and squamous cell carcinoma (SCC-4). The results showed that polyurethane microstructures obtained are stable and have dimensions that make them biocompatible with the biological environment. The cytotoxicity of test samples is dependent on concentration and 72 hours after stimulation at the highest concentration tested the viability of tumor cells was below 50%, the decrease being much more pronounced in the case of squamous cell carcinoma. The novel nanostructures loaded with epigallocatechin gallate induced an augmented cytotoxic effect, suggesting that this drug carriers are suitable to enhance the antitumor effect of epigallocatechin gallate.

Abstract: The main aim of the present in-vitro study is to assess the effect of daily consumable drinks on the aesthetics of the dental composite resin materials. Sixty-four microhybrid and nanohybrid direct composite resin (3M™ Filtek™ Z350 XT Universal Restorative, Filtek™ Bulk Fill Flowable Restorative, USA) block samples were made with a dimension of 15mm X 2mm and are allocated into four groups. Each sample was immersed in test media such as Arabic coffee, black tea, orange-juice and distilled water as control group at room temperature for 15 days (n = 16). The color stability and microhardness measurements were taken at pre-immersion and after two weeks of immersion in test media. These parameters were assessed by electro spectrophotometerusing the CIE (Commission Internationale de l´Eclairage) system and Vickers microhardness indenter respectively. Each group was immersed in its test media for the complete duration of the study. On completion of 15 days, the samples were blot dried out with absorbent paper and microhardness dimensions and color stability measures were performed. The collected data was subjected to statistical analysis to formulate the results. Significant discoloration was observed with the Arabic coffee, black tea and orange-juice compared with control group. The Arabic coffee caused most significant discoloration followed by black tea and orange-juice. Although the highest values of microhardness was noted in the Arabic coffee followed by black tea and orange juice, whereas the lowest values were noted in the control. The color stability and microhardness of the composite resin restorations is affected by the everyday drinks that are consumed, from some more than others. Some of the everyday drinks affect the color stability and microhardness of the composite resin restorations more than the others.

Abstract: The paper presents a theoretical study for the cooling of polymer samples in an injection molding process. The study is applied for neat polylactic acid (PLA), PlA-talc and PLA-starch composite samples representing specimens for mechanical tests reported in literature. A one dimensional model was developed for the heat transport through the thickness of the sample from the polymer to the cooling agent: air in natural convection and water flowing through cooling channels. The heat of solidification of molten polymer was also considered. The model was solved in the frame of Matlab software. The results obtained consist in the evaluation of the final time required to reaches a temperature of about 60°C in the core of the specimen and the evaluation of the temperature profile along the cooling process. When using cooling air in natural convection the temperature profile shows insignificant space variation, but the duration of cooling is about 6 min. The use of cooling water proved to be more efficient in terms of cooling time is about 15-25s, while the temperature gradient in the thickness of the specimen is quite significant at any moment of time.

Abstract: In this study, two different non-ionic surfactants have been evaluated as a plasticizer in lithium polymer electrolytes and compared with an organic carbonate-based plasticizer. To that end, non-ionic surfactants with different molecular weight and structure have been selected (Triton® X-100 and Brij®L23) and compared with organic carbonates (EC:DEC1:1) as plasticizers in lithium polymer electrolytes. The effect of the plasticizer content, salt content and surfactant characteristics on properties such as ionic conductivity, thermal stability and electrochemical stability of lithium polymer electrolytes has been studied. The results obtained show that the non-ionic surfactants studied as plasticizers (Triton® X-100 and Brij®L23) give lithium polymer electrolytes with higher thermal and electrochemical stability than organic carbonates, thus making them promising plasticizers for lithium polymer electrolytes, especially for high voltage lithium-ion batteries. Surfactant structure could influence the ionic conductivity of the polymer electrolytes, with the linear surfactants being more suitable for this application.

Abstract: The aim of this study is to characterize (wettability, surface roughness and gloss) and test (microhardness and diametral compression) four types of light-cured composite resins, one of which is commercial. The first lab-made composite is the reference, obtained by mechanical mixing of three monomers, in equal concentrations. The following two lab-made materials can be considered nanocomposites because they were mechanically mixed in the base solution (Bis-GMA/TEGDMA/Bis-EMA) with α-Al2O3 nanopowders, with a concentration of 5 wt.% for one solution and 10 wt.% for the other. The benchmark material comparison for these lab-made composite and nanocomposite resins is the bioresin system, Filtek™ Supreme Ultra Universal Restorative. Results were promising, especially for the 10 wt.% Al2O3/Bis-GMA/TEGDMA/Bis-EMA system, characterized by mechanical improvment in comparison with the reference composite.

Abstract: The study of the mechanical behavior of materials intended for dental restorations is of crucial importance in the production of a finished product. In the present work, two resins were used for the material matrix, Bisphenol A diglycidyl methacrylate (Bis-GMA), hydroxyethylmethacrylate (HEMA) and a nanofiller (SiO2). This study focuses on the influence of nanoparticle size (30, 50, 100 and 150 nm) on the mechanical properties (flexural strenght and modulus, compression strenght and modulus and work of fracture) of the manufactured composite materials. The results showed improvements in the mechanical integrity of the samples, but differed depending on the size of the nanoparticles added. These differences are closely related to the active surface of the nanoparticles, leading to differences in filler-resin matrix compatibility.