Volume 47, Issue 2

Abstract: Complete dentures technology uses especial heat curing acryllic resins, which are included in DIN EN ISO classification at number 1567, group 1. Polimetacrilates are fragile materials, which fracture easily and often need prosthetic pieces repairs. Evaluation of acryllic resins structural qualities allows choosing of the material with maximum mechanical resistance. Present paper intends to determine some comparative structural studies of three heat curing acryllic resins, concerning behaviour after mechanical testing . There were realized 8 samples from each heat curing resins (Meliodent, Superacryl, and Vertex), using the complete denture technology recommended by the producer. Their mechanical characteristics were determined with help of Zwick Roel equipment. Transversal and longitudinal sections of the fractured zones were evaluated by stereomicroscopy and scanning electron microscopy. Following the mechanical tests, there were obtained the following results: ultimate tensile strength 64 MPa / Meliodent, 66 MPa/ Superacryl, Vertex/ 70MPa; total elongation was 11% for Meliodent, 9% for Superacryl and 5% for Vertex; Young’s elasticity modulus was 4570MPa for Meliodent, 5125 MPa for Supercryl and 6243 MPa for Vertex. By stereomicroscopy there was noticed fragmentation, number of fibres from the transversal cross section, or the aspect, shape, colour of fibre from the matrix. At the scanning electron microscopy, microscopic features may be put in evidence: the aspect of the broken matrix (which is brittle for all the samples), the manner of fracture, the nature of the interface, which is incoherent. Finally the correlation between mechanical behaviour and fracture mechanism was made for dental heat curing resins. Keywords: heat curing acryllic resins, stereomicroscopy, scanning electron microscope

Abstract: This paper presents the influence of the processing temperatures on the physical–mechanical properties of polyoxymethylenes (POM) used in injection molding of high performance sport products. The test-pieces were obtained by processing POM at the following temperatures: 180°C, 190°C, 200°C, 210°C, 220°C, 230°C and 240°C. It was established that the pressure in the mold decreases as the processing temperature increases. Further, thermal analyses (TG, DSC and DMA) were performed and it was noticed that the processing temperature had an influence on the thermal stability of the polymer, but the vitrification temperatures (Tv) and the melt temperatures (Tt) were poorly influenced by the processing temperature. Keywords: polyoxymethylene (POM), injection molding, Thermogravimetry (TG), Differential Scanning Calorimetry (DSC), Dynamic-Mechanical Analysis (DMA)

Abstract: Atomic force microscopy (AFM) has become established as a significant and versatile tool for investigating local mechanical properties of various materials. In addition, through the AFM tip-sample interaction, it has become possible to study the effects of perturbations and modifications to the surface of samples such as composite materials based on polymers that can ensure a transfer selective in the process of friction, trough formed an antifriction selective layer. The selective layer can get by friction between a surface of steel with a sample of composite material (polytetrafluorethylene (PTFE) with added cooper oxide (Cu2O) in various greased media) and formed of very thin layer, tribological performed on surface of steel in which predominated Cu. The accurate knowledge of their response to the continuous AFM scanning could help to design new materials with desirable mechanical properties. In this paper, we present results obtained applying a new method to investigate friction and wear properties on the composite material PTFE/Cu2O. This material is used with high tribological performance at tightening the cylinders of motor vehicles and compressors of petroleum installations. Keywords: atomic force microscopy, selective transfer, substrate, friction and wear, ripple, topography

Abstract: The copolymerization reaction between bisphenol A glycerolate dimethacrylate (BisGMA) and urethane dimethacrylate (UDMA) monomers was studied and the monomer reactivity ratios were determined on the base of the FTIR data obtained at different times of reaction. Both Fineman-Ross and copolymer composition equations were used. Also ProCop computation program was used in order to establish the values for the reactivity ratios. Keywords: Dimethacrylates; Copolymerization; Monomer Reactivity Ratios; FTIR; ProCop

Abstract: Nowadays more and more people have or get sick of venous diseases such as venous insufficiency, low foot blood pressure or even the phenomenon of swelling for diabetic people or for the post-birth period. Medical stockings provide a method to fight against these problems since ancient times but the results after every use was in compliance with the level of technology used to produce the stocking. This situation creates a challenge for the stocking manufacturers with developing new technologies and technical materials that give the best results and maximize the effects of compression stockings on the people that wear them. This paper is integrating the total design of a product, regarding the cycle of the product, profitability and satisfaction of the client problems, proposing new ideas of client approach using new technologies like mass customization through computer integrated manufacturing systems including 3 - dimensional body scanning and individual approaches to the client; and using this knowledge develops a kind of compression stockings that are fit-to-wear and satisfy the requirements of the clients concerning the efficiency of the product, comfort properties and durability. Keywords: compression stocking, yarns, total product design, mass customization, apparel for technical applications, 3-D body scanning, computer integrated manufacturing

Abstract: Two-component injection process has multiple uses from the manufacture of household products to manufacture of high precision parts for industry specific computer and automotive industry. Given the importance the paper presents two-component injection process simulation using plastic material and PPG40 Moldflow software. To realize the simulation it was used a research plan by Taguchi with six input parameters, each parameter with two levels, such as nozzle shape, melt temperature, mold temperature, injection time, injection pressure and accuracy imposed. The main results obtained from simulation show the variation of the mold filling time depending on the injection pressure, temperature distribution on the entire volume variation part and solidification time in matrix material. Keywords:injection, nozzle, temperature, accuracy, simulation

Abstract: The paper presents results concerning the synthesis and characterization as polymer processing aids (lubricants) and/or as tribological lubricants of some monoesters of different monocarboxylic acids with variable length, along with some special aliphatic-aromatic alcohols with a complex structure and/or with superior (larger) alcohols (exclusively aliphatic). The monocarboxylic acids considered were n-butyric, n-octanoic and oleic, respectively, while the alcohols taken into consideration were isodecyl (iso-C10), isotridecyl (iso-C13), as for the aliphatic group, 2-phenoxy-ethanol, 2-[(o-sec-butyl)phenoxy]ethanol, and 2-[(p-nonyl)phenoxy]ethanol, respectively, as for the complex aliphatic-aromatic group. Under these circumstances it became possible to investigate the influence of the structure on the main physico-chemical properties of these synthetic oils as well as on their lubricating characteristics. The results recorded fully certified the validity of the research program. Keywords: complex monoesters, synthetic oils, lubricants, phenoxy-ethanols

Abstract: Nanocomposites were obtained by dynamical melt blending. Some layered silicates and fillers based on nanocarbon were studied as nanofillers. The morpho-structural (XRD, HRTEM), thermal (TGA), dynamic-mechanical (EL) and mechanical (DShD, Ak. si) characteristics were examined. Nanocomposites with intercalated, partially exfoliated/partially intercalated and exfoliated lamellar structure with uniform dispersion of the nanofiller in the polyamide matrix were obtained. The nanocomposites exhibit thermal stability and improved properties as compared to the starting material. Keywords: PA6, nanocomposites, montmorillonite, nanocarbons

Abstract: The susceptibility of starch-based biomaterials to enzymatic degradation by a-amylase and peroxidase enzymes was investigated. A polymeric blend of corn starch with polyethylene, designated by SLDPE, was studied. The degradation was evidenced by gravimetry, scanning electron microscopy (SEM), FTIR spectroscopy, and X-ray diffraction. Analysis performed showed that starch blend is susceptible to enzymatic degradation, significantly in the presence of ionic liquid, as evidenced by increased weight loss and reducing sugars in solution. SEM analysis evidenced the presence of fractures and pores at the materials surface as a result of starch degradation by a-amylase. FTIR spectra confirmed a decrease on the band corresponding to glycosidic linkage (-C-O-C-) of starch. Keywords: corn starch, LDPE/starch blends, degradability, enzymes, ionic liquid

Abstract: Research and Development National Institute for Chemistry and Petrochemistry–ICECHIM, 202 Splaiul Independenþei, 060021, Bucharest, Romania The curing reactions at microwaves for two different systems consisting of diglycidyl ether of bisphenol A (DGEBA) and 4-aminoazobenzene (AAB) and diglycidyl ether of ethylene glycol (DGEEG) and AAB were studied through differential scanning calorimetry (DSC) and FTIR spectroscopy. Keywords : epoxy, azo, microwaves, FTIR, calorimetry

Abstract: Various telechelic bifunctionalized siloxane derivatives were reacted with titanocene dichloride. The reactant functionality is favorable for the formation of the poly(ester), poly(amine), poly(ether), and poly(silyl-ether) depending on the functional groups of the used siloxane precursors. The interfacial condensation technique was applied and, excepting polyesters, in the other cases, the inverse interfacial system was used. CHCl3 was used as a solvent for siloxane phase and triethyl amine was added as a hydrochloric acid acceptor. The very fast reactions occurred at room temperature with colour change from red-orange to yellow. The poly(ester) was also synthesized in solution by using DMF as a solvent. The formation of new structures was verified by FTIR and their thermal behaviour was investigated by TGA and DSC. SEM and Energy Dispersive X-Ray system (EDX) were used to show the morphology of the poly(ether). The repartition of Ti was investigated by EPR. Keywords: siloxane-titanocene copolymers; polycondensation; metallocene; siloxane

Abstract: Mechanism and kinetics of dispersion polymerization of styrene in the presence of a new macromer based on 2-ethyl-2-oxazoline have been investigated. Partial conversion-time curves have been obtained by continuous NMR measurements. Final conversion of styrene was 88% in contrast to 35% for oxazoline macromonomer. The kinetic data proved that particles become sterical stable at 15% conversion. The weight average molecular weight and polydispersity index are in the range of typical dispersion polymerization. The thermal stability and glass transition temperature are increased when a higher amount of stabilizer is used. The presence of the macromer on the surface of the final beads and the fraction of grafted stabilizer were evaluated by XPS. Keywords: dispersion polymerization, macromonomers, 2-ethyl-2-oxazoline, X-ray photoelectron

Abstract: New formaldehyde resins were synthesized by the polymerization of a mixture of 4,4’-methylenedianiline (MDA) and p-tert-butylphenol (p-TBPH) with formaldehyde (FA) (at a molar ratio monomers/formaldehyde, 1/1), in the presence of an acid catalyst (HCl).The mixture of DMF/toluene was used as reaction medium and as carrier for the aqueous condensation. These polymers were characterized by elemental, spectral and thermal analysis and used as hardener for epoxy resins (diglycidyl ether of bisphenol A (DGEBA) and diglycidyl ether of hydroquinone (DGEHQ)). The obtained resins have low molecular weight and are soluble in medium and high polar solvents. The curing and the temperature behaviour of epoxy resin/formaldehyde resin systems were investigated using differential scanning calorimetry (DSC) and thermogravimetry (TG) techniques. The activation energies of the curing reactions are situated in the range of 52 to 66 kJ×mol-1 for DGEBA systems and at 54 to 72 kJ×mol-1 for DGEHQ systems. The cured products have good thermal properties, and the activation energies of the degradation reactions have values between 36-65 kJ×mol-1 for epoxy systems. Keywords: formaldehyde resins, epoxy resin, crosslinking reactions, thermal properties

Abstract: The present study is aimed to investigate the effect of damage due to hygrothermal fatigue on the mechanical behaviour of CFRP (Carbon Fiber Reinforced Polymer) laminates as well as on the skin-core interfacial stress field in sandwich structures having CFRP laminates as core material and aluminum as skin. The above behaviour was both experimentally and analytically studied using a model recently developed by the CMG group at University of Patras. Keywords: hygrothermal fatique, polymeric composite laminates, sandwich structures, interfacial phenomena

Abstract: Damping capacity is comparatively analyzed for a composite with polymer matrix (vinyl ester) and a shape memory alloy (copper-zinc-aluminium). A good damping capacity of shape memory alloy results in structural transformation domain in detriment of composite material. The theoretical model developed on the analyzed material behaviour describes qualitatively the temperature dependence of the dissipation capacity. Keywords: polymer, shape memory alloy, dissipation capacity, fractal

Abstract: Thin foils of poly (vinyl alcohol) (PVA) with different thickness were prepared and dried without modifying their separation surfaces. The induced by stretching under heating birefringence of PVA films was measured under with a Babinet Compensator. An increase of birefringence versus the stretching degree of the PVA foils was evidenced for all studied samples. The dependence of the birefringence on the films thickness was evidenced in this paper. Keywords: birefringence, Babinet Compensator, stretching degree

Abstract: Coefficient of thermal expansion of multiphase composite materials plays an important role in the process of engineered materials design especially while approaching thermal management issues. Tailoring and designing material combinations in order to develop a composite structure to prove stability over a wide range of temperatures, from cryogenic to high values, to withstand extreme environmental conditions is the dream and purpose of any engineering team involved in such study/research area. The paper aims to approach and present the variations of the CTE with extreme environmental conditions (e.g. cryogenic conditioning) for particular combinations of particle-fibers multiphase polymeric composite materials. Influencing factors will be underlined to accompany the experimental research. Keywords: multiphase, polymer, composite, cryogenic, coefficient of linear thermal expansion

Abstract: The implants surfaces investigated in the present study were modified with the films of poly (vinyl) alcohol (PVA) which were formed in physiological serum (0.9% NaCl). Surfaces evaluation included electrochemical measurements such as linear potentiometry (LP) and electrochemical impedance spectroscopy (EIS). These suggest that PVA acts by adsorption at site on the metal surface and formed a compact, adherent and uniform layer. The composition of layer was estimated using Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM/ EDX) and X-ray Photoelectron Spectroscopy (XPS) techniques, which confirm the adsorption of PVA on the surfaces, through –OH groups, with a specific affinity to the titanium sub­strate. Keywords: titanium electrode; electrochemical measurements; poly (vinyl) alcohol; SEM/ EDX; XPS

Abstract: Polymeric matrix composite materials are used when high characteristics are needed, good resistance under severe working conditions and low specific weight. Implementing polymeric matrix composite materials, specially, glass reinforced ones, resulted in the substituting of classical materials, whose quantities are more, and more, limited. Composite material products can be obtained to their final shape when manufacturing or, when necessary, can be submitted to further machining processes. Polymeric matrix composite materials can be conventionally machined (cutting, turning, drilling, milling or broaching) or / and non-conventionally machined (laser, ultrasound, etc.). Researches on milling machinability of glass fibers reinforced polymeric composites are at their very beginning, in our country, this paper pointing out some important aspects of research on cutting forces in cylindrical-face milling. There is also presented a data measuring, acquisition and processing system for the experimental model, as well as a real time control scheme designed to determine the measuring errors. Keywords: polymeric matrix, glass fibers, milling, cutting forces, automation system

Abstract: Atomistic molecular modeling based on forcefield simulations, dissipative particle dynamics (DPD) mesoscale computational method and electrochemical techniques are here used to investigate the mechanical properties, structural morphology and electrochemical response of poly(pyrrole) (PPY )- poly(aniline) (PANI) conductive polymer composite. Computational bulk models of PPY-PANI were implemented at atomistic- and meso-scale and composite films were made available by electropolymerisation on platinum support. Further data concerning mechanical properties, structural morphology and electrochemical response of PPY-PANI composite films were collected by means of in silico investigations, scanning electron microscopy (SEM) and cyclic voltammetry (CV). Both approaches showed that the new formed composite material behave as new material with enhanced characteristics when compared with single component. Concerning material morphology and mechanical properties, simulated bulk systems were homogeneous and their Young’s moduli ranged from 0.04 to 0.475 GPa depending on the material composition. Based on CV measurements, it is stated that the electrochemical activity, reversibility, electrical conductivity and cycle-life stability of the PANI-PPY composite is significantly higher than the pure conducting polymer. Keywords: PPY-PANI films, atomistic- and meso-scale modeling, mechanical testing, electrochemical properties

Abstract: A series of bismaleimides were used to prepare polymers in an attempt to achieve materials with improved properties. Structurally different bismaleimide compounds were synthesized by the reaction between 3(4)-maleimidobenzoylchloride with various diphenols having or not substituents to the aromatic rings. Polymers based on these compounds were prepared by the Michael addition of diamine to bismaleimides. Fourier transform infrared (FTIR), proton nuclear resonance (1H-NMR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and atomic force microscopy (AFM) were used to characterize these materials. Keywords: bismaleimide monomers and polymers, thermal characterization

Abstract: The multilayer structure consisting of alternative sheets of paper and ethylene-propylene elastomers was investigated for electrical applications. The changes in the main electrical characteristics, namely volume resistivity, dielectric loss, permittivity were determined for the evaluation of material stability under accelerated degradation promoted by g irradiation. The satisfactory response of this sandwich structure is illustrated by sample resistivity placed around 1015 W.m, permittivity less 2.025 and dielectric loss not higher than 0.04. The correlation between degradation effects and electrical properties is presented. Keywords: electrical insulation, synthetic rubber, cellulose, multilayer structure

Abstract: The aim of this work is to obtain and characterize some collagen/hydroxyapatite composite materials obtained by collagen matrix immersion in SBF, for different immersion times. The obtained composite materials were characterize by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy detector (EDS) and complex thermal analysis. The main differences between the composites obtained by different immersion times can be visualized by SEM images. The increasing immersion time lead to a more compact composite material, with lower porosity as exhibited in the recorded SEM images. On the other hand, not only the morphology is changed but also the composition of the composites. At high immersion time, onto the composite materials, sodium chloride (NaCl) crystals can be observed. The presence of NaCl can be easily identified by XRD and, based on the relative characteristic peaks intensity can be quantified. Keywords: SBF immersion, collagen matrix mineralization, morphological changes versus immersion time

Abstract: This paper presents a failure model applicable for unidirectional fibers reinforced composites that point out the fiber-matrix interface role in the mechanics of the failure process. The model is applicable in any plane stress state case. The ABAQUS/Standard finite elements program is used to point out the applicability of failure model. The deformation of a square plate with the dimensions of 100x100 mm, having a hole with the diameter of 50 mm in the middle, was analyzed. The plate is realized from composite materials with unidirectional fibers oriented at an angle of 45o. The visualization and the interpretation of the simulation results have been made with the help of ABAQUS/Viewer module. The obtained diagrams reflect a very good concordance between the predictions of the failure model and the results provided by other models. This confirms the hypothesis on whose basis the unidirectional composite failure model was formulated. Keywords: composite materials, failure, unidirectional fiber glass, polyester resin

Abstract: In this paper, we obtained experimentally the elasticity modulus and tensile strength, for four types of composite materials made of epoxy resin reinforced with wheat straw, with different spatial orientation for reinforced. Using experimental results, we have obtained the original formulas, for the calculus of tensile strength and elasticity modulus, for the types of specified materials. These relationships are dependent on the percentage of fibers oriented in the direction of request, and which have the length equal with the test sample. In the case in which the percentage is equal to unit, the relations coincide with the ones from unidirectional composite materials. We determined experimentally the coefficient of internal damping and eigen frequencies, for bars embedded at one end and free at the other, made from epoxy resin reinforced with wheat straw, targeted unidirectional, bidirectional and random. Keywords: composite materials, elasticity modulus, tensile strength, damping coefficient, wheat straw

Abstract: Mesoporous silica was obtained by the acid attack of a serpentinite rock. This material was soaked with acrylonitrile (containing azobisisobutyronitrile as initiator) and the radical polymerization led to the obtaining of polymer inorganic-organic nanocomposites. The polymer nanocomposites were transformed in carbon-silica nanocomposites by the cyclization and graphitization of the carbon chain polymer. Heating the carbon-silica nanocomposite in nitrogen atmosphere allowed the synthesis of silicon nitride, a raw material for special ceramics. Keywords: radical polymerization, nanocomposite, silica, silicon nitride

Abstract: The internal friction phenomenon in metallic and polymeric shape memory materials is analyzed. The experimental results permit validation of a theoretical model which describes qualitatively the temperature dependence of the internal friction for the investigated materials. Moreover, theoretical model accepts not only evaluations of different states of material (solid state structural transformations as martensite – austenite) but also materials very different as nature (metallic or plastic). Keywords: shape memory polymers, damping capacity, internal friction, martensitic transformation

Abstract: Polyacrylonitryle (PAN) fibers are used on a large scale in textile industry but, some sorts of PAN fibers are valuable precursors for specific carbon fiber (CF) due to their best fitness to the purpose e.g. for high strength CF or for active CF. The application of PAN as precursors of CF is based on its specific structure and texture. Thus, the properties of PAN base CF strongly depend on PAN structure, texture and fiber morphology. In this respect, the paper addresses the modeling of PAN fiber structure and texture and, subsequently, estimation of structure and texture parameters based mainly on Wide Angle X-ray Diffraction (WAXD) technique but, on SEM and other data. The PAN fiber structure and texture parameters were calculated on the basis of classical X-ray diffraction theory applied to paracrystals. The preferred orientation parameters were calculated on a wide accepted model. The main structural parameter of PAN paracrystal d200, d201, and L200 and preferred orientation/texture parameters Z, [cos2 u], P (cos2 u) of the PAN fibers were determinated. Based on WAXD data it was calculated the PAN fiber crystallinity. As it results from the paper the WAXD technique seems to be the best from the efficiency-cost point of view for PAN structure and preferred orientation characterization. Keywords: WAXD, SEM, structure, preffered orientation, polyacrylonitryle fibers