Volume 47, Issue 4

Abstract: The present work provides new insights about the micro and nanostructure of native starch granules from potato and maize by scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM images revealed the shape and the size distribution of the granules as well as some features, such as holes and wrinkles, on the surface of granules. These data were confirmed by AFM observations which showed the presence of numerous protrusions (nodules) on the granules surface of both starches. The structure of granules surface consisted of small spherical particles of about 30 nm in diameter, identified particularly for potato starch. These nanoparticles might be related with highly branched amylopectin molecules in substantial agreement with amylopectin blocklets (of about 20 nm) model. Larger particles of about 60 nm up to 80 nm were also visualized especially on the surface of maize starch granules representing different associations of amylopectin and amylose. The largest elongated particles of about 100 nm to 200 nm found randomly on granules of both starches might be assigned to arise from the granule-surface components, such as starch carbohydrates attached to granule proteins and phospholipids, in general agreement with starch granule surface composition data. This investigation also supports the complex structural network for the starch granule surface (periphery) and its role in maintaining the integrity of starch granules and in the starch gelatinization process. Keywords: starch granules, potato starch, maize starch, granule surface, supramolecular structuring, scanning electron microscopy (SEM), atomic force microscopy (AFM)

Abstract: Experimental thermal properties on carbon nanotube with polymer matrix composites are analyzed. Increasing of thermal conductivity with carbon nanotube percentages enhancing is obtained and some phenomenological considerations on the heat transfer mechanisms are presented. Keywords: carbon nanotubes, thermal conductivity, effusivity

Abstract: Physical properties, such as thermal and dielectric characteristics, of some aromatic polyimides which contain methylene units have been investigated. The results indicated that the polymers were highly thermostable with decomposition temperature over 450°C and low dielectric constants. The thermogravimetrical values processed by differential method Freeman-Caroll showed that the activation energies and reaction orders are lower in air than in nitrogen. Keywords: methylene units, polyimides, thermal characterization, activation energy, dielectric constants

Abstract: Modulus I interlaminar fracture toughness of wood laminated composite materials has been evaluated using the critical strain energy release rate associated with the onset of crack growth in double cantilever beam specimens (DCB). The advantage of using the DCB test for determining the critical strain energy release rate in the case of wood laminated composites relies on the working method which is focused on failure analysis in adhesive layer through the presence of initial interlaminar crack, but also due to the energetic approach in deduction of calculus relations. Data analysis was conducted by two methods namely, the corrected compliance method which is based on the linear elastic fracture mechanics principles, and the area method which accounts the whole shape of load-displacement curve obtained through a complete loading-unloading cycle. In general there is a good agreement between the results obtained by the two methods and those reported in literature. Keywords: wood laminated composites, interlaminar fracture, critical strain energy release rate, Double Cantilever Beam (DCB) specimen

Abstract: This paper presents an experimental study aiming to obtain a new polymer composition by using styrene-butadiene radial block-copolymer with styrene-butadiene diblock-copolymer blend, in order to manufacture masking solution for metal protective coating in the chemical milling process. Keywords: styrene-butadiene block-copolymers, masking solution, protective coating

Abstract: This paper presents the influence of processing temperature on the physico-mechanical properties of polypropylene (PP) used at the injection molding of performance sport items. The test-pieces were molded at the following real injection temperatures: 220, 240, 260, 280 and 300°C. It was determined that the in-mould pressure decreases with the increase of processing temperature The thermal analysis performed were: TG, DSC and DMA. It was established that the processing temperature influences the thermal stability of the polymer molded at 300°C, but the vitrification temperature and the melting temperature are slightly influenced by the processing temperature. The storage modulus E’ is influenced by the processing temperature and stress frequency. Keywords: polypropylene (PP), injection molding, Thermogravimetry (TG), Differential Scanning Calorimetry (DSC), Dynamic-Mechanical Analysis (DMA)

Abstract: Poly(amide-imide)/polyaniline blends containing 2% and 10% polyaniline have been prepared by casting the dispersion resulting from the mixture of polyaniline (micrometer size) with poly(amide-imide) in tetrahydrofuran as solvent onto glass plates. Polyaniline has been synthesized by chemical polymerization of aniline in the presence of (NH4)2S2O8 followed by dedoping with ammonium hydroxide. The poly(amide-imide) has been obtained by solution polycondensation of a fluorinated bis(o-aminophenol), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, with a diacid chloride having imide rings and hexa-fluoroisopropylidene unit, namely 2,2-bis[N-(4-chloroformylphenyl)phthalimidyl]hexafluoropropane. The thermal properties and sensitivity of pure poly(imide-amide) and its blends with polyaniline to vapors of acetone, ethanol and liquefied petroleum gas were investigated. All samples showed high thermal stability, decomposition temperature being above 270°C. They exhibited sensitivity to the tested gases, those containing 10% polyaniline presented the greatest sensitivity to acetone vapors. Keywords: polymer blends, polyaniline, poly(amide-imide), thermal stability, sensors

Abstract: In this paper, it is showed that a mechanical model with one degree of freedom can be used to study the vibrations of a bar in a certain point. The considered structures were made of epoxy resin reinforced with carbon and carbon-kevlar texture. The vibrations in the free end of the bar, clamped at the other end, were determined experimentally for four different lengths. Eigenfrequencies and damping factor for the first modes of vibration were obtained for each bar. Relationships for the eigenfrequency and damping factor are proposed, as a function of the length of the bar, for each of the studied materials. Keywords: Eigenfrequency, damping factor, composite bar

Abstract: The paper presents the effects of the miscibility and of the micro-structure on the surface defects of some bio – hybrides based on starch, polyvinyl alcohol (PVOH) and multilayered silicates. At macroscopic level (100m) the studied starch bio-hybrids seem to be compact materials. If these materials are analysed at a microscopic level (10 m) depending on their type surface defects like voids, cracks and fractures can be observed. These defects are not a consequence of a poor miscibility, even in case of bio-hybrids that contain untreated silicate. These defects appear because of the bio-hybrids micro-structure. As the new bio – hybrids are probably disorderly ones, it can be estimated that the surface defects appear as a consequence of a poor distribution of the swollen silicate tectoids into the polymeric matrix, possibly as a consequence of the improper melt processing conditions. Keywords: polyvinyl alcohol, starch, multilayered silicate, surface defects, miscibility, bio-hybrides, micro-structure

Abstract: We have used light-cured experimental (Restacril, Nanopacryl, C-foto T, CP-AD1, CP-AD3) composites colouring tests ”in vitro”. The tests were performed on samples of 30 mm diameter and 2 mm thickness, which were immersed in coffee, red wine, and two food colouring agents (red, containing Sunset yellow (E110) and carmoisine (E122), and yellow, containing Sunset Yellow, tartrazine (E102) and Ponceau 4R (E124)). The samples were subsequently removed from the solutions, rinsed with water and dried, and then measured after three days and later after 2 months. On the 2 months-old samples, a bleaching gel was applied (G4, 35%), and the samples were again measured after three hours and after 24 h. The measurements were performed with a UNICAM UV-Vis spectrophotometer. For analyzing the color DE*= f((L*a*b*)) with a spectrophotometer, three discs per composite were prepared. From the reflection spectrum the color coordinates (Da*, Db* DL*) were determined and the color difference. Keywords: dental composites, colour, dental bleaching

Abstract: The paper reports the performances of the polysulfone-polyaniline (PSf-PANI) porous composite membranes for various ratios PSf / PANI in membranes. Polysulfone-polyaniline porous composite membranes are obtained by phase inversion with chemical reaction. PANI is obtained in-situ by oxidative aniline polymerization. Composite membranes are morphologically studied by electron microscopy and characterized by thermal analysis and water solutions permeation at different pH and pressures. Polysulfone-polyaniline porous composite membranes UF processes performances to BSA separation are also reported. Keywords: PSf-PANI membranes, phase inversion, hydrodynamic characteristics, rejection, BSA

Abstract: (Nano)composites based on maleated ethylene propylene diene terpolymer (EPDM-g-AM) and organically modified montmorillonite (OMMT) has been prepared by melt intercalation procedure. The materials were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), dynamic scanning calorimetry (DSC) and mechanical tests. XRD data show the increase of the distance between the silicate layers indicating the intercalation of polymer chains in the montmorillonite galleries. The incorporation of OMMT in composites determines the increase of melting peak temperature (Tm) and heat of fusion (DHf) suggesting a supplementary nucleation increase due to the OMMT presence. The mechanical properties were analyzed as a function of the OMMT level in the composite and the results reveal remarkable improvement relative to the conventional composite. Keywords: EPDM-g-MA/OMMT nanocomposites, XRD, TGA, DSC, mechanical properties

Abstract: Mechanical properties of the new bromobutyl rubber-based composite (BrBR) were evaluated in comparison with similar NBC protection materials, used either in Romanian Army or in other NATO country armies. The following parameters were determined: mechanical strength, tensile strength and elongation, and the tear force – trouser-shaped test specimen. From the data obtained, a real improvement of the break parameters of BrBR, both in warp and in weft, versus the performances of Romanian materials in use was noticed. Also, versus the foreign materials, the material obtained presents properties basically between the French material and the German one. Keywords: NBC protection, composites, mustard gas, mechanical properties

Abstract: Porous polysulfone (PSF) beads and composite beads (PSF-Cu-MT-Sil) obtained by incorporating copper-metallothionein functionalized silica in a polysulfone solution were prepared using the phase inversion method. Their characteristics were investigated with experiments of swelling, Fourier transform infrared (FTIR) spectroscopy and SEM microscopic analysis. Polysulfone and composite beads were used in catalase (CAT) immobilization. The kinetics of the biocatalytic process, stability under different temperature conditions and the inhibitors effect were studied as major factors on the immobilized catalase activity. The present work is meant to demonstrate the potential of crosslinked polysulfone and especially polysulfone with copper- metallothionein beads for the enzyme immobilization process. Keywords: polysulfone, composite beads, catalase, enzyme immobilization

Abstract: Composite materials of different composition were obtained by utilizing either a polyethylene or polypropylene matrix and a wood flour filling. In order to characterize these materials, a series of experiments were conducted to determine density, electric strength, complex dielectric constant components and and dielectric loss factor tgd for various electric field frequencies and at different temperatures. The results show that the dielectric properties are heavily influenced by the filler content with very high registered values in the case of low frequency electric fields and high temperatures. It can be ascertained that samples having a polypropylene matrix have superior electric properties than those having a polyethylene matrix. Finally, the opportunity for utilization within low voltage and industrial frequency electrical engineering applications of the tested composite materials is shown. Keywords: wood-polymer composites, dielectric properties, dielectric spectroscopy

Abstract: A polyurethane (PU) based on 4,4’diphenylmethane diisocyanate (MDI), copolyester poly(ethyleneadipate) diol (PEA) and extended with butylene glycol (BG) was synthesized via a two steps polymerization technique. The thermal stability of the PU was investigated by thermogravimetric analysis (TG) at temperatures between 30 and 600oC. The synthesized PU was irradiated in an UV exposure unit as such the spectral distribution of the light was a good match for terrestrial solar radiation (200 h, l > 300 nm, Ia = 30 mW cm-2). The modifications in the chemical structures of the PU before and after irradiation were characterized using Fourier transform infrared spectroscopy - attenuated total reflectance (FTIR-ATR) technique. The yellowing index variation (YI) exhibited a systematic trend increase with irradiation time. Our results are in agreement with the formation of quinoide structures, which are colored products resulting from photo-degradation of PU. Keywords: polyurethane, thermal analysis, photostability, thermal stability

Abstract: In this study, blends of biodegradable matrix as poly(3-hydroxybutyrate) (PHB) and fibers provided by renewable resources were prepared by a melt blending method. Improvement of the compatibility between fibers and polymer was studied using coupling agents: maleic anhydride (MA) respectively, succinic anhydride (SA). Mixtures with two types of fibers were investigated in terms of microscopy, torque, density, tensile strength, melting temperature and contact angle. It is found that the mechanical properties of PHB with cellulose fibers blends were better than PHB and wood fibers. Keywords: polyhydroxybuthyrate, wood fiber, cellulose fiber, coupling agent, blend

Abstract: A series of phosphorus-containing polyesterimides has been synthesized by solution polycondensation reaction of an aromatic dianhydride, namely 1,4-[2-(6-oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl)]-naphthalene-bis(trimellitate)dianhydride, with various aromatic diamines. The polymers were easily soluble in polar organic solvents, such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, tetrahydrofuran and chloroform. They showed high thermal stability, the decomposition temperature being above 400oC and the glass transition in the temperature range of 174-194oC. Due to the presence of phosphorus the polymers gave high char yield in thermogravimetric analysis. Solutions of the polymers in N,N-dimethylacetamide showed photoluminescence in the blue region. Keywords: polyesterimides, phosphorus-containing polymers, good solubility, thermal properties, photoluminescence

Abstract: In the idea of improving the performances of both full and removable partial dentures, new materials and technologies are coming on the market, promising a better quality. Thermoplastic materials are used more and more widely in the technology of complete or removable partial dentures due to their superior qualities. Thermoplastic resins are suitable for manufacturing a wide range of removable partial dentures without metallic structure, in optimal conditions of biocompatibility. By injection, we have manufactured several removable partial dentures without metallic structure. Full denture casting currently represents a technological alternative. The casting system we tested, usually uses reversible hydrocolloids for investing wax patterns. Besides the system’s own advantages, the authors also noticed certain errors consecutive to casting, materialized in lack of substance and the development of porosities on the mucosal facets of the complete denture bases. Keywords: removable partial dentures, thermoplastic materials, molding-injection devices, casting, full dentures, errors

Abstract: The paper is focused on the behavioural simulation of the intraocular organic lenses, defined by geometric characteristics (the accumulation radius, thickness and diameter) [1] and material characteristics, for a certain incident wavelength [2]. The simulation provides a picture of the ray-tracing for the second and third reflection/refraction. At the same time, the user can display the print of a ray on a normal plane related to optical axis direction. The authors designed the simulation program, aimed to evaluate the wounded through the multiple reflections in the spectre available for chosen material. Thus the disparity of a certain parameter will influence the transference through lenses for some radiation or spectre. The paper is designed to be used in optics, to shape the refractive components, and can predict the useful diameter of lenses, diaphragms or aperture stop. Keywords: organic optical glass, optical layout, multiple reflections, imaging

Abstract: In order to point out the intrinsic peculiarities of thermorheodynamical behaviour of solid-like polymer materials, the framework of a Zener - Arrhenius model is considered, the frequency or/and temperature dependences being approached in the case of strain-controlled conditions. The complete set of the explicit general relations providing the characteristic thermorheodynamical quantities (the storage, loss and absolute moduli, as well as the loss factor, and the corresponding storage, loss and absolute compliances) is presented in terms of meaningful rheological parameters including the low - and high frequency limit values of the storage modulus, and the appropriate relaxation time. The underlying analytical relations are given in forms suitable for direct numerical simulation of both isothermal frequency - dependence, and well as of isochronal temperature - dependence circumstances. Keywords: analytical relations, characteristic thermorheodynamical quantities, strain-controlled conditions, Zener - Arrhenius model, isothermal and isochronal circumstances

Abstract: 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

Abstract: 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

Abstract: 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

Abstract: 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

Abstract: 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

Abstract: Fiber-reinforced polymeric composite materials present an orthotropic distribution of their mechanical and elastic characteristics. This behaviour is mainly due to the fact that the fabric used behaves differently under the same type of stress, on different directions. The procedure described by our paper enables researchers to determine the elastic modulus of such materials, on three different directions, using a specially designed specimen. The finite element analysis revealed that there were no significant influences on the strains and deformations existing in the measurement area, concerning the shape of the test specimen or its fastening. The results obtained for three composite materials used to validate the procedure showed that two of the materials having orthotropic properties, exhibit different elastic modulus. Keywords: polymeric composite, deformations, octagonal specimen, orthotropy, elastic characteristics