Volume 48, Issue 1

Abstract: Acid polyurethane of hard type was prepared to be further treated in hydrothermal conditions at high pressures of 20, 40, 60 and 80 atm. The influence of pressure on chemical structure and morphology of macromolecular chains have been investigated using Fourier transform Infrared Spectroscopy (FT-IR) and Differential Scanning Calorimetry (DSC). Three endothermic peaks appear in hydrothermally treated polyurethanes, being related to conformational changes due to polymer shrinking, decomposition and melting. Their corresponding enthalpies increase with pressure, probably due to a more compact polymer structure at high pressure. Under the influence of pressure, macromolecular chains modify their conformation and approach each other, leading to an increased density of the hydrogen bonds. Stretching vibrations of the –C=O group are shifted from 1746 to 1724 cm-1. There is an optimum pressure (60-80 atm) range where the polyurethane presents an increased capacity of interaction through carbonyl groups (r1 =1.295 at 60 atm) which is favorable for further composite synthesis. Keywords: acid polyurethane, high pressure, hydrothermal process, IR spectroscopy, DSC

Abstract: This paper presents the radiation stability of epoxy resin modified with different amounts of titania (1, 5 and 10 %). The isothermal chemiluminescence investigation performed at 1500C has pointed out the high radiation stability of investigated systems. The sharp decrease in the early stage of oxidation emphasizes the benefit brought by the filler. Even though the initial chemiluminescence intensity enhances with filler content, the oxidation level after 20 min does not essentially differ. The application of high irradiation doses up to 1000 kGy does not affect the thermal stability of composites. Keywords: radiation stability, epoxy resin, chemiluminescence intensity, filler

Abstract: The present paper studies the effect of the diameter of single walled carbon nanotubes (SWCNTs) on mechanical properties of SWCNTs reinforced epoxy resin composites. Bulk atomistic models of epoxy resin-SWCNTs with different compositions were built and were subject of an extensive multistage equilibration procedure. Molecular dynamics simulations were used to estimate glass transition temperature (Tg) and Young’s modulus of epoxy resin and epoxy resin/SWCNTs composites. The Young’s moduli generally increased with increasing of SWCNTs content and values range from 1.83 GPa in the case of pure epoxy resins to 3.21 GPa for epoxy resin/SWCNTs (8,8) composite system. Overall, the agreement between predicted values of the material properties and experimental data in the literature is satisfactory. Keywords: atomistic molecular modeling; mechanical properties; SWCNTs- epoxy resin composites, glass transition temperature

Abstract: This work presents the main mechanical properties of the pressure sensitive adhesives solutions based on carbocatenary elastomers: peel, shear and tensile strength. Polychloroprene rubber was chosen as the main component of the adhesive system and its adhesive performances were evaluated. The mechanisms of fracture of the adhesive bond and breaking at the tensile test were also discussed. Keywords: pressure sensitive, adhesives, elastomers, polychloroprene rubber

Abstract: This paper presents a study that underlines the importance of the choice of polymer dispersions in the composition of an exterior emulsion paint in order to improve its quality with respect to the action of external factors. All these properties which facilitate the application and increase the durability are due to the homogeneous distribution of inorganic particles in an organic binder. In order to emphasize this influence, various types of polymer latexes were used: a dispersion of an acrylic copolymer and methacrylic ester, but also combinations thereof with a potassium silicate solution, with silicone latex, with a colloidal suspension containing an alkyd resin with 70% solids dissolved in White Spirit, by comparison with a dispersion of nano silica particles in an organic polymer. All these types of paints which were obtained were analyzed by measuring their hardness, contact angle, elasticity, dirt pickup and chalking resistance, color retention during accelerated (artificial) aging, water vapor diffusion and water permeability, thus proving the existence and efficiency of the inorganic particles of the paint composition. Keywords: acrylic dispersion, silicone paints, -acrylic-silicon, solvent based alkyd resins, accelerated aging resistance

Abstract: Fracture toughness occurring in a material that has micro-cracks may be improved by particle addition, these particles having different properties than the basic material. This paper includes the outcome of a research on the influence of softer or harder particles added to the basic material, on the stresses occurring in the immediate vicinity of micro-cracks. Our research is designed to determine to what extent this process may result into preventing a crack from advancing into the material subject to unfavorable loads, depending on the direction of that crack. The outcome we achieved using finite element analysis supports the assumption that, by adding a certain amount of particles, which have specific characteristics, to the basic material, fracture toughness may increase significantly. Keywords: inclusion, crack, stress, finite element analysis, hard and soft particles

Abstract: This work reports on a study concerning the behaviour of the reinforced beech beams with CFRP (carbon fiber reinforced plastic) under a bending load. An experimental program was proposed to characterize the strength response of CFRP-wood beams. Mechanical tests on the reinforced wood showed that CFRP materials may produce flexural displacement and lifting increases of the beams. Observations of the experimental load–displacement relationships showed that bending strength increased for wood beams reinforced with CFRP composite plates (Megaplate), compared to those without CFRP reinforcement. Keywords: carbon fiber, bending strength, wood, pretension device

Abstract: Safety requirements are becoming more and more important in terms of polymers interaction with fire, while various flame retardant additives are being expelled for their adverse effects on the environment. This is the reason for the research challenge for new effective and environmentally friendly flame retardant systems. In this view, the objectives of the present study were the synthesis of the 2,4,6-triiodophenyl acrylate (TIPA) monomer and of p(MMA-co-TIPA) copolymer; and the determination of the reactivity ratios of the comonomers. As foreseen, MMA reactivity is obviously superior to TIPA (r1 = 5.49 and r2 = 0.053), and a decrease of initial copolymerisation rate is noticed as the feed enriches in MMA. Keywords: reactivity ratio, 2,4,6-triiodophenyl acrylate, homopropagation

Abstract: This paper outlines the results of a series of experiments designed and conducted by the authors in order to determine the mechanical properties of a new composite material used for manufacturing the sleeves for the consolidation or reinforcement of the zones with local surface defects (flaws) in transport pipelines. The analysis and interpretation of the results allowed the authors to: assess the effectiveness of the new composite in repairing pipelines with local metal loss defects; establish the most effective way of preparing the pipeline surface for the application of the new composite sleeve; and to emphasize the correlation between the elastic properties of composites and the consolidation or reinforcement effect on the corroded or damaged pipelines following the application of composite sleeves. Keywords: pipeline maintenance, composite sleeve or wrap, mechanical properties of composites

Abstract: The paper proposes a way of using of the recycled rubber for the manufacturing of a hybrid composite material based on epoxy resin, reinforced both with glass woven fabrics and with recycled rubber. One presents the mechanical characteristics of this composite material, measured in: flexural test by using the method of the three points and impact testing with Charpy pendulum. The work also describes some aspects concerning to the effects of the water absorption on the mechanical behaviour in flexural testing after 2980 h (124 days) of immersion in water, at room temperature. Finally, the experimental results obtained were comparatively analysed for both the dried and wet specimens. One could remark a degradation of the mechanical characteristics (elastic modulus E, flexural strength s, mechanical work W until the maximum force). Concerning the impact behaviour, it was measured the failure energy U and then computed the resilience K (impact strength). It was observed that additionally reinforcing with rubber particles leads to the increasing of the resilience K. Keywords: hybrid composite; recycled rubber; absorption; bending; impact

Abstract: This study followed the value of thermographic investigation in interrelation of polymeric materials with oral mucosa in patients with complete dentures, respectively thermal surface changes at completely edentulous patients, with and without stomatitis, using ThermaCAM PM 350. Thermograms revealed an elevated temperature under the denture, thermal values corresponding to mucosal aspects (edentulous without dentures, dentures wearer, normal or congested mucosa, flabby ridge) and prosthetics (suction degree), with asymmetrical color distribution of the thermal field in oral mucosa, respectively denture surface. Polymeric material shows a similar temperature rise to the mucosa (thermal impression) and residual heat. Thus, thermography may be a method of polymer-oral status interrelation assessment in denture wearers, providing important information in prevention, diagnosis and treatment of oral diseases, acquired in relation to polymer dentures. Keywords: polymeric material, oral mucosa, complete denture, thermography

Abstract: The paper presents the main aspects of dynamic modelling of steel/plastic geared systems with high gear ratios in relation to the nonlinear parameters, such as time-varying mesh stiffness and load sharing alternation. Firstly, the specific aspects of geometrical design criteria for helical gear with small number of pinion teeth are presented in order to prevent the negative phenomena of the involute tooth generation and gear engagement. Then, the dynamic analysis is conducted to investigate the shared dynamic loads and dynamic transmission error of steel/plastic gear pairs along the line of action. The effects of the time-varying mesh stiffness are incorporated in the nonlinear dynamic model for numerical analysis. An improved model of the mesh stiffness is developed by including specific meshing characteristics of helical gear pairs. The variation of the dynamic transmission error is simulated and examined in relation to the teeth number, addendum modification coefficients and input torques. A computational algorithm is developed for instantaneous dynamic contact analysis. Keywords: plastic gears, high gear ratio, mesh stiffness, dynamic transmission error

Abstract: In this paper, the behaviour of polyamide 66 with 30% short glass fibers (PA66 GF30) is investigated using instrumented indentation technique combined with the dynamic mechanical analysis (DMA). The visco-elastic-plastic behaviour of PA66 GF30 is described by a rheological model which incorporates a spring, a plastic element and Kelvin-Voigt elements. The time-temperature superposition (TTS) principle was used to investigate the effect of time and temperature on the behaviour of PA66 GF30. Keywords: indentation, polyamide 66, creep, dynamic mechanical analysis

Abstract: A phosphorus-containing copoly(ester-amide-imide) 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 4,4´-oxydianiline and isophthaloyl chloride. The polymer was easily soluble in polar organic solvents, such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, tetrahydrofuran and chloroform. The polymer shows high thermal stability, the decomposition temperature being above 410 oC. The value of the glass transition temperature was 231oC. Due to the presence of phosphorus, the polymer gave high char yield in thermogravimetric analysis. Keywords: copoly(ester-amide-imide), phosphorus-containing polymer, thermal stability

Abstract: This research studies the influence of scratches on the polyethylene gas pipes after squeezing with the squeeze-off tool in order to stop gas flow due to an intervention of the gas pipeline. Problem occurs when there is a need to make a decision whether it is safe to squeeze the pipe with scratches. The goal of the research is to determine the change in the depth of scratches on the polyethylene gas pipe after squeezing with the squeeze-off tool. After the experimental research it was determined that there would be a change in the depth of scratch. The change of the depth of scratch positioned on the squeeze-off ear would be considerably bigger when compared to the depth change of a scratch positioned under the upper cylinder of the squeeze-off tool. Based on the resulting data, it is a recommendation of the author not to squeeze the pipe if it has scratches. If the squeezing if inevitable on the place where there is a scratch, the squeeze-off tool needs to be positioned under the upper cylinder of the squeeze-off tool. Keywords: scratches, polyethylene gas pipes, gas flow,the squeezing

Abstract: 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

Abstract: 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

Abstract: 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

Abstract: 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

Abstract: The main goal of this study was to investigate the capacity of dendritic polymers to encapsulate the antitumoral drug (5-fluorouracil) using non-covalent methods. As nanoscale containers four polyamidoamine dendrimers (PAMAM) types of different generations were used. The antitumoral drug encapsulation efficiency of these dendrimers was pointed out using different methods like FTIR Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS) and Thermogravimetric analysis (TGA). The obtained results showed that the dendrimers generation exhibits a strong influence on the 5-fluorouracil encapsulation. Keywords: dendrimer, antitumoral drug, FTIR analysis, X-Ray Photoelectron Spectroscopy