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The present study is focused on a multidisciplinary research, regarding the durability of complete dentures realised from light curing UDMA resins. Absence of methyl, ethyl, propyl or butyl monomers from their composition is responsible for their good utilization, because they do not generate contact allergies. For testing there was used Eclipse Prosthetic Resin System (DENTSPLY International Inc. - DeguDent GmbH, Hanau Germany), which consists of: Base Plate, Set-Up and Contour Resins. Using the technology recommended by the producer, there were realized nine samples, which were mechanically tested with Zwick Roel equipment. A pair of finite prostheses, realized with the help of this system, was used by finite elements method (3D scanning, software Pixform Pro Program, program CAD – Ansys Workbench (ANSYS Multiphysics) or ABACUS / CAE version 6.6.1). Static analyses for stress and strain were based on „reverse engineering” method. In the end, experiment certification took place also through fatigue tests (Walter-Bai Dynamic Testing Machine). The following mechanical parameters were determined after testing: Young’s modulus of elasticity: 2908.45 MPa, ultimate tensile strength Rm= 59.49 MPa; total elongation At= 4.582 %, at a medium force value of 1203N. Stress and strain analysis of the denture subjected to different loadings, was revealed through chromatic spectres on denture virtual models. The warm colours indicate the areas with problems. By finite elements method one can realize noninvasive numerical procedures, which reveal the risk areas that can lead to dentures’ fracture; thus, one can correct and improve the complete dentures quality. Following the fatigue tests, we may consider that mechanical properties of Eclipse allow a five years warranty for complete denture. Key words: complete dentures, light curing resins UDMA, finite elements analysis, fatigue

PEHD plastic materials are more and more used in applications. Their possible physical and chemical changes, depending on the temperature changes and time, in a given atmosphere, can be made by simultaneous measurement of the sample mass and its temperature. It is achieved by the use of thermogravimetry (TG). The thermogravimeter Mettler Toledo presents thermograms or thermogravimetric curves as well as their differentials. Results obtained in this way can be starting points for next researches. Keywords: PEHD, thermogravimetry, thermogravimetric differentials, quantitative analysis

When great damages occur on gas-pipes, a quick intervention is often needed, as close to the place of damage as it can be. That is the reason why recently it has more and more been used a procedure of squeezing the pipe using a squeeze-off tool and thus stopping the flow. After the damage has been removed, the deformed pipe returns to the original shape by using re-rounding clam and the flow is established again. After the above-described process, the pipe is permanently deformed, as far as shape and thickness are concerned. The size of the deformation is important for the assessment of further use of the existing pipes or for determining the parameters for the newly-projected pipes. So far, the researches have been dealing with the hydrostatic and stress states after the squeezing of the pipe. The subject of this research is the decrease of the pipe thickness after the squeezing, and the goal is to help the designers of distributive plastic gas-pipes to determine the pipe wall thickness, as well as to help the managers of distributive networks so that they would know what happens to the existing gas-pipes after the intervention on the pipe. Keywords: sqeeze – off tool, polyethylene gas pipe

The paper presents results on wear after testing a class of composites (PA +1% black carbon and different 5 concentrations of micro glass spheres) and discussions about damaging processes within the superficial layer, grouped in two categories: one favouring the material remove and the other the reduction of wear intensity. The analysis points out that tribological behaviour should be interpreted only by putting together information about wear, friction, temperature in contact, pair of materials in contact in order to obtain sustainable results that could be useful in engineering design. Keywords:micro-nano particles, polyamide, wear, IR thermogravimetric, SEM

Conformational parameters, and free and Van der Waals volume values for a group of polymers containing methylene bridges, some of them having methyl substituents as well, have been calculated and correlated with physical properties such as solubility, glass transition and decomposition temperature, tensile stress and dielectric constant which were measured for these polymers. Thus, it was shown that conformational rigidity determines the packing of macromolecules in solid state, and therefore the free volume, and glass transition temperature and dielectric constant. The presence of methyl substituents and other flexible groups such as isopropylidene, carbonyl or hexafluoroisopropylidene has a more complex effect on the values of mechanical properties. Keywords: polyimides, thin films, conformational parameters, glass transition, dielectric constant

This work aims to present the optimization of the design of a plastic part manufactured at Accurate Machine and Tool Ltd. Canada, by using Moldflow [1] combined with the optimization method developed by Dr. Genichi Taguchi. The method uses statistical principles and involves reducing the variation in a process through robust design of experiments. The experimental design proposed by Taguchi uses orthogonal arrays to organize the parameters affecting the process and the levels at which they should be varied; it allows for the collection of the necessary data to determine which factors most affect product quality with a minimum amount of experimentation, thus saving time and resources. Moldflow allows part designers and mold makers to predict the manufacturability and quality of their design during preliminary product development stages. It helps to select the best injection gates configuration, as well as the values of mold temperature (Tw), melt temperature (Tm) and an optimized body shape for a part in order to minimize variability in a key performance measure. This presentation discusses the application of these tools on a real life production of the parts. Using this method, with a modest number of simulations runs, the resultant savings are significant. The part has the weight reduced from 0.03lb for the initial part to 0.022lb. On this one design alone it is saved 27% of the material for each part. Keywords: polymers, injection molding, design, optimization, Taguchi Method

Thermal analysis, mass spectrometry-coupled, of partially hydrolyzed polyvinyl alcohols, for suspension polyvinyl chloride technology, showed that the reduced blockiness of low hydrolyzed product induced a low thermal stability with three degradation stages. When high blockiness is obtained, thermal stabilities in excess of 273°C are attained, regardless the hydrolysis degree. Glass transition of polyvinyl acetate segments is always present for hydrolysis degree ranging from 47.8 to 88.7 mol %. The melting transition is exhibited only by samples with hydrolysis degree higher than 74 mol %. Keywords: polyvinyl alcohol, TGA-MS, thermal stability, polyvinyl chloride

Water sorption/desorption behaviour of the materials is very relevant for their application in pharmaceutical, food, sensor, electronics, fuel cell and biomedical fields. The sorption/desorption equilibrium, which is related with the plasticity and mechanical properties of the materials, as well as the kinetics of water sorption/desorption, which is related to the transport properties, are interesting research areas. The fully automated gravimetric analyzer is an equipment for rapid evaluation of the moisture sorption capacity in dynamic regime. The ultrasensitive microbalance measures the weight modification as the humidity is changed in the sample chamber at constant regulated temperature. Water vapour sorption behaviour of some materials belonging to different polymeric classes with various structures and morphologies were investigated. Keywords: water sorption, dynamic vapor sorption, isotherm

A series of six experimental dental copolymers of different compositions has been prepared from new synthesized Bis-GMA-type oligomers and triethyleneglicol dimethacrylate by photochemical initiation of polymerization. The paper studies the influence of the chemical composition upon the extent of polymerization, mechanical properties and water sorption of the experimental copolymers. The corresponding commercial Bis-GMA-based copolymers were used as control. The extent of the polymerization, determined by FTIR method, ranged between 61.67% for the new copolymers containing 75% bis-GMA-type oligomers and 79.6% for the new copolymers containing 50% bis-GMA-type oligomers in the matrix. From the comparison of the mechanical properties, we came to the conclusion that the values for compressive strengths and diametral tensile strengths were in the same range to those obtained for the corresponding commercial Bis-GMA-based copolymers, while the flexural strength values were higher than the values for to corresponding control copolymers. The water sorption values were in the limit of clinical requirements. Keywords: dental resins, extent of polymerization, mechanical properties, water sorption

The use of ultrasonication can be an useful tool to improve the properties of the collagen/hydroxyapatite (COLL/HA) composite materials. The aim of this paper is to study the influence of the ultrasonication on the synthesis and characteristics of the COLL/HA composite materials. Especially based on the microscopic analyses it can be observed a more uniform distribution of the HA, practically the HA covering the collagenous materials. The integrity of collagen was studied by FTIR, comparing the COLL/HA composite spectrum of the sample obtained by ultrasonication with that of the control sample (no ultrasonication was applied). Due to no changes observed at the C-O region and due to the unaltered ratio between the peaks intensity (between the intensities of the peaks from 1450 and respectively 1240cm-1) of the two composite materials it can be asserted that ultrasonication does not alter the structure of collagen. The resulted composite materials were characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Keywords: collagen/hydroxyapatite nanocomposite; transmission electron microscopy (TEM), ultrasonication