In space filed usually size doesn’t matter but weight does, being a critical point in space structure design stage. Carbon fiber reinforced polymer composite materials are already deployed in many space applications, due to their intrinsic characteristics, mainly their high strength/high stiffness to weight ratio and potential for zero or near-zero CTE, coefficient of thermal expansion. The paper presents the results of the study made on advanced composite exposed to extreme conditions comparable to those found on space environment (Low Earth Orbit – LEO [2000 km). The samples were manufactured from CFRP epoxy composite with different thicknesses (1.2 mm, 1.8 mm, 3.7 mm, 7.7 mm) using autoclave technology. The 1.8 mm thickness samples were coated with 50 and respectively 100 µm of Zn using arc thermal spray technique. Specimens were exposed to UV, gamma radiation and thermal cycles. The results of microstructural, morphological analysis and mechanical characterization showed the aging and damage mechanisms developed post exposure in comparison with reference materials.
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The present paper aims to examine the way in which the temperature is distributed when the polyethylene sockets are welded using the electrofusion procedure. This research is necessary because in practice certain problems occur relating to the destruction of these sockets during welding or later. The survey is conducted in cooperation with companies working in the field of welding in polyethylene, complying with the required standing standards.
A series of bismaleimide monomers and polyaspartimides with various structures were synthesized and their structures were confirmed by Fourier transform infrared (FTIR) and proton nuclear resonance (1H-NMR) spectroscopy. Chain extension of bismaleimides was accomplished by incorporating various ether or other groups. Polymers based on these bismaleimides were prepared by the Michael addition of diamines with various structures to bismaleimides. Thermal and dielectric properties of these polymers were studied.
adhesives over acrylic classic prosthesis, but the literature lacks in comparative studies that investigate the effects and advantages of denture adhesives on obturator prosthesis performance. The hypothesis for this study was that the use of the denture adhesive would improve both wearing and efficiency on obturator prosthesis. We evaluated the clinical behaviour of six acrylic obturator prosthesis made on various maxillary defects, with and without a denture adhesive. The adhesive was applied on the prosthesis as recommended by the manufacturers. Patients used the adhesive for 24 hours and, through a questionnaire, they evaluated (comparative with and without adhesive) There are many studies in the literature regarding the effect of denture the following aspects: prosthesis retention, duration of retention, masticatory efficacy, cleansing of dentures, cleansing of gums. The clinical retention of the dentures was correlated to Modified Kapur Index Scale (MKIS) for denture supporting tissues.
The aim of this study was to asses the flexural strength of provisional acrylic resin fixed partial dentures reinforced with glass fiber with the provisional restorations without reinforcement. Three group of specimens were prepared for the flexural strength: Poly Methyl Metacrylate (PMMA) acrylic resin provisional restoration without glass fiber (control), acrylic resin provisional restoration reinforced with glass fiber between the abutments and acrylic resin provisional restoration reinforced with glass fiber including the abutment and the pontic of the fixed partial denture. The flexural strength was tested with a servo-hydraulic testing machine (Zwick Proline Z005 device), with a maximum 5KN force The highest resistance to deformation and fracture was registered in acrylic resin provisional restoration reinforced with glass fiber including the abutments.
In present paper there are given the results concerning wear behaviour in Ringer’s solution of four titanium alloys with 5%Mo, 7%Mo, 11%Mo and 12%Mo. Structural investigations (made by both optic, electronic microscopy and X-Rays diffraction) revealed a dual phase structure consisting from alpha martensite and beta”solid solution, with the constituents proportion depending on molybdenum content. Wear rates were determined using a Talysurf profilometer in Ringer’s solution for the experimental titanium-molybdenum alloys. Finally, the beneficial influence of molybdenum on wear behavior was put in evidence: the higher molybdenum content is, the lower friction coefficient is.
A novel assay for the electrochemical detection of 4-nonylphenol (4-NP) based on carbon nanotubes modified screen-printed carbon electrodes (CNTs-SPCEs) has been investigated. The electrochemical behavior of the modified SPCEs and the mechanism of the oxidation of NP were investigated using cyclic voltammetry. The differential pulse voltammetry parameters were optimized for quantitative determination of 4-nonylphenol. A detection limit of 9.95·10-6 mol·L-1 was obtained for 4-nonylphenol using its oxidation signal at +0.25 V. The disposable sensor showed good performance and was applied for the determination of 4-nonylphenol in tap water with satisfactory results.
The obtaining of polymers with special properties is dependent on both conditions and materials used in the formation process. This work presents the obtaining, by using the sol-gel method (and citric acid used as in mixture fuel), of some powdery materials destined to be used as additives in polymers’ formation. Different types of salts were used in the powders’ obtaining process, the long term purpose being to add special properties to polymeric materials, such as good electrical conductivity or photovoltaic capabilities. The materials and methods are thoroughly presented, proving the obtaining repeatability of these powders. Different characterization techniques were used and presented in this paper, from Scanning Electron Microscopy (SEM) for morphology, to EDX for elemental composition, Raman scattering for vibrational properties, thermal analysis by differential scanning calorimetry (DSC), and electrical resistivity for electrical conductivity calculation.
Surgical sutures properly conducted will ensure maintaining the edges of the flaps until the wound healing process allows withstanding the functional stress. Among the possible complications of surgical sutures, we can find the wound suppuration, as a result of contamination with germs. In our in vitro study about the degree of bacterial adherence to different types of suture materials we chose four types of suture materials (three absorbable and one nonabsorbable) exposed to 4 bacterial species (Staphylococcus aureus, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa). The monofilament absorbable polydioxanone wire had the lowest bacterial adherence, followed by the multifilament nonabsorbable wire of silk and the two types of multifilament absorbable polyglycolic acid wires. Regarding the bacterial species tested, Enterococcus faecalis had the highest adhesion level, no matter what type of material or time of exposure has been used.
Because the petroleum based products have a negative impact on the environment,is necessary to create and use eco-friendly lubricants. Vegetable oils are part of this category because they are a renewable natural resource, environmental safety, and show lubricating characteristics. By mixing the castor oil with two synthetic diesters (isodecyl and 2-[(p-nonyl)phenoxy]ethyl adipate respectively, isotridecyl and 2-[(p-nonyl)phenoxy]ethyl adipate) were obtained two series of new lubricants to which the physico-chemical and rheological characteristics were studied. The lubricants were also characterized using the differential scanning calorimetry (DSC) and thermal gravimetric (TG) analyses. The obtained mixtures present superior properties to mineral oils and can be used as lubricants.