Volume 47, Issue 1

Abstract: Poly(N-vinylcaprolactam)-poly(ethylene glycol) – poly(N-vinylcaprolactam) triblock copolymers were synthesized for the first time by the ATRP of N-vinylcaprolactam (NVCL) initiated from poly(ethylene glycol) (PEG) macroinitiators with 2-chloropropionate groups at both ends and catalyzed by the CuCl/5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (Me6Cyclam) system. Their polydispersity was larger than 1.8, indicative for a lower control degree of the process, which was ascribed to the slow deactivating behaviour of the catalytic system. The triblock copolymers synthesized displayed thermosensitive behaviour in aqueous solution, undergoing sol – gel transition on the interval 30 - 60°C. It was found that the aggregation (cloud point) and gelation temperatures, as well as the rheological properties of the polymer aqueous solutions depended on the chain length of both PEG and PNVCL blocks. Keywords: N-vinylcaprolactam, poly(ethylene glycol), triblock copolymers, ATRP, thermal gelation

Abstract: The replacement of glass fibers polymer composites with those containing polymers and cellulose fibers, friendly for environment and human health has gained a special importance in recent years. The paper presents some mechanical and thermal characteristics of composites of neat polypropylene and jute fibers from technological wastes, treated and untreated. The use of waste fibers in polypropylene led to a significant increase of the elastic modulus and tensile strength which highlights the reinforcing effect of the waste fibers, the effect being more important in case of jute fibers treated with aminosilane. Keywords: polypropylene, composites, jute, mechanical properties

Abstract: Nanoxide based composites are suitable materials for advanced medical application. Fe3O4, CoFe2O4 and MnO2 nanoparticles, synthesized by different soft chemistry routes (precipitation in the presence of soft template and solution combustion) were coated by a biocompatible polymer, sodium alginate. The oxides and corresponding composites were structural and morphological characterized. The saturation magnetization for Fe3O4-based composite is 10.1 emu·g-1, resulting magnetic domains of 5.2 nm that suggests a superparamagnetic property. Radical scavenging capability of the composites was investigated by two different methods, Trolox Equivalent Antioxidant Capacity (TEAC) and peroxide-chronoamperometry. Keywords: ferrites, MnO2 , oxide-based composites, biopolymer matrix, radical scavenger

Abstract: Thin films, in the range of tens of micrometers thickness, have been prepared by casting onto glass plates the N-methyl-2-pyrrolidone solutions of two poly(ether imide)s containing isopropylidene or hexafluoroisopropylidene groups. The polymers have been synthesized by solution polycondensation reaction of 4,4’-(1,3-phenylenedioxy)dianiline, with 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride or 1,1,1,3,3,3-hexafluoro-2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride. The dynamic mechanical analysis and dielectric spectroscopy were employed to study thermal and electrical behaviour of polymer films. Keywords: poly(ether-imide)s, thin films, dynamic mechanical analysis, dielectric spectroscopy

Abstract: The paper focuses on rheokinetic investigations on matrix of a new composite material. A simple, yet effective, experimental method has been employed to measure several parameters that can help, by resin’ viscosity measurements, in finding resin kinetic hardening parameters. As it is shown by one of our papers [1.3,4] CFRAl (Carbon Fibers Reinforced Aluminum) is a new hybrid composite under development . It has unique and promising properties, with foreseeable excellent results in applications requiring a reliable, yet light, reinforcement material that can also withstand powerful thermal shocks. Keywords: rheokinetic model, composite material, carbon fibers, bullet-proof material

Abstract: Polysulfone based membranes with controlled porosity pore density, size and orientation were synthesized. The predicted pore characteristics are obtained by adding magnetite (nano or micro) particles into the polysulfone gel and the pores obtained by applying different magnetic fields. The pore density, size and orientation can be designed based on the magnetite particle concentration, on the magnetite particles size and respectively based on the angle between membrane surface and magnetite field. The pore density, size and orientation of the membranes were analyzed by SEM. FTIR was used to investigate the membrane composition and to prove the possibility of removing the magnetite particles by acidic dissolution or by extended membrane exposure to the magnetic field. The complex thermal analysis was used to characterize the thermal behaviour of the synthesized membranes. Keywords: polysulfone membranes, pore characteristics, predicted porosity and separation ability, scanning electron microscopy

Abstract: This study refers to the obtaining of mortar plasters using perlite and polymer additives additions. The performed study has outlined the infuence of the polymeric additive nature and content as well as perlite addition on mortar plasters based on hydraulic binders characteristics. Keywords: mortar plasters, polymeric additive, perlite, redispersabile powders, cellulose ethers

Abstract: In this paper a modern multi-objective optimization of the pneumatic ejectors of the plastic injection mold is presented. For this Pareto multi-objective optimization, two objective functions (volume and efficiency of the ejector) and four genes were taken into consideration and a set of twelve constraints were formulated. In solving the optimization problem we used an original two-phase evolutionary algorithm (2PhEA) inspired from the concept of “punctuated equilibrium”. 2PhEA is implemented in Cambrian v.3.2 which is in operation at the Optimal Design Centre of the Technical University of Cluj-Napoca, Romania. The study on the individuals along the obtained Pareto front reveals some important conclusions useful in the design of the pneumatic ejectors. Keywords: optimal design, evolutionary algorithms, pneumatic ejector, injected part

Abstract: The extraction of surface geothermal energy using heat pumps represents a recent topic in specialty literature. This paper presents a numerical model for modelling the thermal field around the heat exchangers mounted in the soil. The purpose of modelling is to reveal the dynamics of heat exchange between the soil and the polyethylene pipes and highlighting the variation in temperature field around the heat exchanger. Keywords: Geoexchange, heat pump, polyethylene, thermal field

Abstract: In the recent years the utilization of polymeric materials increased due to their good mechanical properties and easy manufacturing. Starting from automotive industry up to food industry polymeric materials are used for obtaining components by molding or by machining. Taking into account the wide range of applications, it is important to know the mechanical behaviour of these materials in different loading conditions. Accordingly, this paper presents an experimental study to determine mechanical properties on 11 commercial polymeric materials. Tensile and shear static tests and impact tests on notched and un-notched specimens were performed. The results are presented comparatively, and two new parameters were introduced for material selection purpose. Keywords: mechanical testing, polymer materials, tensile strength, shear strength, impact strength

Abstract: In the presented paper experimental results on welding polystyrene and optical elements are shown. On the basis of the obtained results on shearing-stretching and macroscopic analysis of the work pieces, conclusions are drawn regarding the weld when using ultrasonic welding process. Key words: ultrasounds, welding, plastic materials

Abstract: Most of the problems of modern engineering are solved using numerical methods. In order to use a numerical method the first step that must be performed is to generate a numerical model that contains all the input data in terms of geometry, material data, boundary conditions (loads and support). Ideally a structure must be defined only using hexahedral elements that are capable to provide the best results. This paper presents a method for generation a fully hexahedral finite elements model using a grid based procedure. The method is a good support for the engineering involved in product design. An application to a plastic manufactured part is presented. The results obtained using the all hexahedral finite elements models are compared with the results obtained using a numerical model generated using conventional techniques. Keywords: numerical model, hexahedral finite elements, mesh generation method

Abstract: This work paper proposes an elastic displacement field for a composite bar made of two constituents (phases). The deformation hypothesis described by this field is built in full respect of all the conditions of compatibility concerning deformation and strain-stress status of any kind. More else, the conditions of continuity concerning the surface separating the two constituents are also fully satisfied. Using this new displacement field we show that the tangent to each and every point of the characteristic curve built for this composite material depends only on the size of external charge (loading) and the longitudinal deformation of the composite bar. Based on these facts we also show that the constitutive equation of this composite material is a non-linear one: in fact it is a concave curve the way that the slope of the tangent to each and every point of the characteristic curve is decreasing as the deformation increases. We have released three sample groups with different arrangements of reinforcing fibers from one group to any other one and we have established the characteristic curve for each and every sample group. Using these curves we have obtained the longitudinal elasticity modulus, the tension at break, the elongation at break as well as the slope and the ordinate at the origin for the tangent to the breaking point of the characteristic curve. The characteristic curves have the shape (allure) suggested by the theoretically obtained results. We have shown that a certain parameter characterizing the non-linear behavior of the composite material is given by the ratio between the longitudinal elasticity modulus and the value of the slope of the tangent to the breaking point of the composite material characteristic curve. Keywords: composite materials, characteristic curve, elasticity modulus

Abstract: The paper describes some aspects concerning the effects of the type of wood species on some mechanical characteristics of some hybrid composite materials reinforced with both E-glass woven fabric and wood flour. It also shows the effects of the moisture absorption on the mechanical behaviour in bending after immersion in two different environments: water and seawater. The specimens were manufactured by reinforcing a polyester resin Copoly 7233 with both E-glass woven fabric EWR145 and wood flour. Two kinds of wood flour, oak wood flour and fir wood flour were used to manufacture the two composite materials tested. The immersion time was approximately eight months. The quantity of the moisture absorbed was greater in case of the immersion in water than in case of the immersion in seawater. Then, the both dried specimens and the wet ones were subjected to flexural tests by using the method of the three points. Finally, the experimental results obtained were analysed in terms of the nature of the immersion environment. Moreover, it was analysed the effect of the immersion time on the changing of the mechanical characteristics in case of woven fabric / oak wood flour / polyester. Finally, the paper recommends the using of the oak wood flour in case of the parts made of composite material analysed, that works in humid environment excepting the case when its salt content is greater. Keywords: hybrid composite; wood flour; absorption; flexural test

Abstract: Numerous studies have shown that the geometry of the femur and pelvis affects the distribution of the occurring tensions and movements. The study was performed on the 3D model (three dimensional), of the coxofemoral joint which was achieved through CT images (tomography computer). The results confirmed that the values of tensions and displacements slightly differ from those in the literature due to the geometry and the properties of the used material. Keywords: finite element analysis, hip joint, mechanical properties, modelling

Abstract: Polymers become more important in everyday life. Although extremely useful in their life cycle, polymers become long-term pollutants. Worldwide, along the increased research in the environmental field, one can obviously observe a keen interest into new biodegradable and biocompatible plastic materials. This paper presents the synthesis and characterization of a new class of biodegradable copolymers based on carbohydrates. An oligomer was synthesized by the polycondensation of 3-benzyl-5,6-(bis(maleyloxy))-1,2-isopropylideneglucofuranose with propane-1,3-diol in the presence of p-toluenesulfonic acid and then it was copolymerized with hydroxypropyl (meth)acrylate, using benzoyl peroxide as initiator. The oligomer was characterized by FTIR, NMR spectroscopy and HPLC-MS, and the copolymers were analyzed using FTIR and thermogravimetry. Keywords: glucose, glycopolymer, maleic anhydride

Abstract: The paper presents the multidisciplinary studies dedicated to the minimization of the residual stresses in an Acrylonitrile-Butadiene-Styrene part. The first stage of the study consists of an experimental research employed to measure the physical characteristics of the polymeric material. The next stage is a simulation of the moulding process for a plate-wise specimen made of the material previously tested, being interested by the values of the residual stresses. The next stage is the experimental research of the residual stresses by the use of the hole-drilling method applied on the previously simulated plate-wise specimen. The results of the two studies are close one to the other and the conclusion regarding the material and the parameters employed for the simulation are used for the next study dedicated to the simulation of the moulding process for a complex part. Several studies were performed in order to find the best parameters of the moulding process which lead to a minimum level of the residual stresses. Other parts made of the same material may be also simulated in order to minimize the residual stresses. We conclude considering that a high degree of confidence regarding the results of the numerical model may be achieved only if the results of experimental studies are employed. Keywords: polymeric part, residual stress, experiment, numerical model, applications

Abstract: Platinum nanoparticles with sizes between 10 and 42 nm have been obtained by a sonoelectrochemical method in the presence of a water-soluble polymer, poly(amidehydroxyurethane) (PAmHU), which acted as a coating agent. The PAmHU stabilized Pt nanoparticles were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), UV-Vis and FTIR spectroscopy and dimension distribution and Zeta potential analysis. The analyses showed the fact that these nanoparticles are capped by the polymer, which confers them water-solubility and stability. Keywords: platinum nanoparticles, poly(amidehydroxyurethane), sonoelectrochemical synthesis

Abstract: This paper presents the preparation by phase inversion of polysulfone and cellulose acetate ultrafiltration membranes (UF1-UF36) with various amounts of PEG additives (1000, 2000, 4000 Da), designed for the whey protein separation. To establish optimal operating conditions for membrane separation and the membrane with the best characteristics for the ultrafiltration of whey, we determined the flow variation of the two types of whey (pH=6.21, pH=4.35) with different parameters: whey temperature, operating pressure, protein retention and clogging phenomenon. All the results indicated that at the same protein separation efficiency (MWCO), the polysulfone membranes present higher flows than cellulose acetate membranes and their use in the acid whey ultrafiltration process lead to a whey protein concentrate with a protein content about 5 times higher than the initial whey content (6.4 kg/m3). The best protein retention 98.73% was obtained for UF18 membrane (20% PS, 2 % PEG 4000), with optimal flow rate (23.9·10-6 m3/m2s) for acid whey, operating at 50oC and 106 Pa. Keywords: membranes, ultrafiltration, proteins, recovery

Abstract: A series of poly(ester urethane)s were synthesized, containing, poly(e-caprolactone) diol of Mn= 2000 as soft segments. Each series used the same diisocyanate in the hard segment, i.e., 1,6 hexamethylene diisocyanate, with the same content. The polyurethane polymers were prepared by a two-step polymerization in the absence of catalyst, at the molar ratio of OHsoft segment /NCO/ OH chain extenders = 1/2/1. The chain extenders were 1,12-dodecan diol, glycerin and castor oil. For all polymers the structures were determined by FTIR, the physico-chemical and thermal properties were determined by thermogravimetric analysis and additionally tensile properties as well as Shore A hardness were analyzed. Poly(ester urethane)s with castor oil exhibited higher tensile strength (up to 27 MPa vs 30 MPa) and elongation at break (up to ~780% vs. 1000%) in comparison with the corresponding glycerin poly(ester urethane)s. Keywords: polyurethane elastomers, chain extenders, crosslinkers, mechanical properties, thermal behaviour

Abstract: The paper presents the preparation of two new 3-D nanocomposite porous materials, based on collagen type I (COL) and b-tricalcium phosphate nanopowder (n-b-TCP) and the selection of the best method for their chemical cross-linking using 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide hydrochloride (EDC). To our knowledge, no EDC cross-linked COL/n-b-TCP composite materials for orthopedic use were reported. The physico-chemical and biological properties of the cross-linked composite materials were investigated by porosity, dissolution, enzymatic degradation and cytotoxicity analyses. Key words: carbodiimide, nano-beta-tricalcium phosphate, collagen, cross-linking, biocompatibility