Volume 46, Issue 2

Abstract: Gypsum/ poly(butyl acrylate) composites have been prepared based on natural gypsum and the monomer butyl acrylate by means of gamma irradiation. The conversion of polymerization was followed up with respect to the irradiation dose using thermogravimetric analyzer (TGA). The data show that yield of polymerization increases with increasing the irradiation dose. A yield of about 98% was achieved by exposure of the samples to a dose of 5 kGy. A thermomechanical analyzer (TMA) was used to locate the range of the glass transition temperatures (Tg) using the mode with alternative variable force; the mode with constant force was used to determine the Tg of the pure polymer and the composite prepared at the same irradiation dose. Also differential scanning calorimeter (DSC) was used to ensure the location of the glass transition temperatures. Keywords: Gypsum; polymer composites; butyl acrylate; polymerization; radiation

Abstract: Three types of polyhedral oligomeric silsesquioxane (POSS) compounds were used to synthesize nanocomposites based on urethane dimethacrylate (UDMA). An advanced characterization of POSS compounds was done by X-Ray Photoelectron Spectroscopy (XPS) for chemical structure, X-Ray Diffraction (XRD) for crystalline phase and Differential Scanning Calorimetry (DSC) for thermal transitions. The POSS compounds generally influence the thermostability of UDMA-based nanocomposites acting both as a comonomer and reinforcing agent. Keywords: polyhedral oligomeric silsesquioxanes, XPS, XRD, DSC, nanocomposites, TGA

Abstract: The study presents experimental data regarding the curing reactions of some epoxy systems consisting of diglycidyl ethers of bisphenol A and different amine hardeners at room temperature and at microwaves. The curing reaction of the system composed of an epoxy resin (ROPOXID P 401) and 4,4’-diamino-diphenylmethane (HT 972) was studied by differential scanning calorimetry (DSC) and FT-IR spectroscopy. The degree of conversion obtained using FT-IR method is very close to that obtained using calorimetric method. Keywords: epoxy, amine, microwaves, kinetic

Abstract: Two types of aromatic-aliphatic polyimides have been synthesized: polyaddition polyimides, from the Michael reaction between 4,4’-diaminodibenzylbismaleimide and ethylenediol (diethyleneglycol respectively) and solution polycondensation polyimides, from the reaction of 5-(2,5-dioxotetrahydrofurfuryl)-3-methyl-3-cyclohexenyl-1,2-dicarboxylic acid anhydride (epiclon) with 4,4’-diaminodibenzyl [1,4-bis(p-amino phenoxy)benzene respectively]. All monomers and polymers were characterized by conventional methods, and the physical properties of the polymers, including solubility, thermal, optical, electrical or mechanical properties were discussed. Keywords: bismaleimides, Michael reaction, epiclon, aliphatic polyimides

Abstract: The dynamics of the plasma discharge through spontaneous symmetry breaking as double layer Langmuir, anodic patterns etc., is treated by means of the fractal description. Considering that the charge carrier movements take place on fractal curves, the electric charge transport is studied in an extended model of scale relativity. Using the motion equation for the complex speed field for the irrotational movement the generalized Schrödinger equation is obtained, and in the absence of dissipation a generalized Korteweg de Vries type equation is obtained. The process is also analyzed at the microscopic scale, when the electrical conductance increase is controlled by means of the soliton coherence. When the external field exceeds a critical value, the solitons which stocks the energy break down and simultaneously release the energy to the environment. The same mechanism can explain the charge transport in composite materials (e. d. nanostructures). Moreover, some correspondences between the theoretical model and the behaviour of the patterns generated by laser ablation are analyzed. Keywords: fractal space-time, charge transport mechanism, nanostructures, composite materials

Abstract: The aim of this study is to obtain and characterize a range of hybrid polymeric films with different collagen content and synthetic poly-alcohol as polyethylene glycol (PEG). Films were obtained using a “casting solution method” by a cross-linking process at room temperature. The new collagen hybrid biofilms are devoted to cell growth and proliferation. Keywords: collagen gel, hydroxyapatite, ternary hybrid biofilms

Abstract: The paper describes aspects concerning the effects of the immersion time in water, on some mechanical characteristics of some composite materials reinforced with E-glass woven fabrics. The specimens were manufactured by reinforcing a polyester resin Copoly 7233 with both woven fabric EWR300 made of E-glass fibres and chopped E-glass fibres. The hand lay-up technology was used to manufacture the specimens with different pressures in the moulding step: low pressure and high pressure, respectively. The first of all, some specimens were immersed in water and the data regarding the moisture content were periodically recorded. Then, the wet composite specimens were subjected to the flexural test (three point method) after 3500 h of immersion and 7417 h of immersion, respectively. Finally, the experimental results obtained in case of the immersed specimens were comparatively analysed with the results recorded in case of the dried specimens subjected to the bending test too. Moreover, the mechanical characteristics of the specimens were analysed taking into account the different manufacture methods used. It is also shown a comparison concerning the results obtained in cases of the two kinds of reinforcements used. Keywords: composite; moisture; absorption; flexural test

Abstract: An assay on the thermal stability of isotactic polypropylene stabilized with Sanduvor PR 31, a hindered amine (O1-(1,2,2,4,6,6-hexamethyl-4-piperidyl) O3 - (1,2,2,6,6-pentamethyl-4-piperidyl) (2Z) – 2 - [(4-methoxyphenyl) methylene] propanedioate, was performed. The oxidability of modified polymer previously subjected to weathering treatment or UV irradiation was investigated in air by isothermal (1550C) and isobaric (normal pressure) oxygen uptake. The exposure time was sufficient enough to attend a slow degradation rate (281 days for weathering test and 550 h for accelerated UV ageing). The main kinetic parameters, oxidation induction time and oxidation rate, were determined from the dependencies of chemically consumed oxygen on testing time. Comparative results on reference samples (control or stabilized polypropylene) and degraded materials are analyzed for depicting the influence of ageing factors on the polypropylene durability. Keywords: polypropylene, UV degradation, weathering, oxygen uptake, Sanduvor PR 31

Abstract: Graphite-based Teflon composites find various applications in many engineering fields. For certain applications, the use of composites rather than metals has in fact resulted in savings of both cost and weight. The usage in many fields demands several machining operations to be performed on engineering polymers. The paper deals with two different materials: polytetrafluoroethylene with regenerated graphite (PTFE GR) and polytetrafluoroethylene with 32% carbon and 3% graphite (PTFE CG 32-3). At the beginning of the study it was performed an advanced characterization for both materials that have been used: PTFE GR and PTFE CG 32-3. The chemical composition was determined using X-ray photoelectron spectroscopy (XPS). Complementary information about the chemical structure is obtained with Fourier transform infrared spectroscopy (FTIR). This combination of spectroscopic methods was used to establish individual differences between the chemical structures for the used materials. Second part of the present paper investigates the effect cutting parameters on the cutting force in the turning of PTFE GR and PTFE CG 32-3 materials. The effects of different parameters on cutting force are analyzed and presented in this study. This paper presents that the success of the machining operation is affected by the chemical structure of the work material. Keywords: engineering polymers, spectroscopy analysis, cutting force, turning

Abstract: The UHMWPE has a plastic behaviour but it is specified only the surface wear, unless the evaluation of the great importance of this behaviour of plasticity for the calculation of the depth of penetration. This work tries to demonstrate the fact that there are components of the wear by plastic deformation. Also, by this type of wear an explanation of smooth surface of the UHMWPE in the contact zone, after millions of gaits cycles may be explained Keywords: hip endoprosthesis, wear, penetration depth, roughness, plastic behavior

Abstract: This paper presents the synthesis of complex nanostructures of the Fe3O4-n[SiO1.5g-(CH2)3(NH2)](NH2)nd-(GL)ne type [Fe3O4 = magnetic core; n[SiO1.5g-(CH2)3(NH2)] = coated layer; (NH2)nd,-NH2= surface and deep amino groups which play an important role in biochemical interfacing; (GL)ne= exterior superficial glutaraldehyde layer]. These nanostructures have several interesting physical and chemical characteristics, such as: biochemical fixing without destructing the microorganisms on the Fe3O4-n[SiO1.5g-(CH2)3(NH2)](NH2)nd-(GL)ne surface and the ability to differentiate the microorganisms in magnetic field, according to the mass and volume. In order to obtain superior biochemical fixing performances we have analysed and determined the chemical and physical distributional mechanisms of (NH2)nd, -NH2 groups on the surface and in the depth of the above-mentioned nanostructure. For this purpose we have deduced the control equations according to the synthesis parameters, which triggers the growth of the silicone polymer layer and the distribution of the amino groups in its structure. Keywords: Magnetite, coated nanoparticle, biochemical fixing, crosslinking molecules

Abstract: This paper presents the influence of processing temperature on the mechanical-physical properties of thermoplastic polyurethanes (TPU) used at injection moulding of performance sport products. The test-pieces were moulded at the following real injection temperatures : 200°C, 210°C, 220°C, 230°C and 240°C. It was determined that the in-mould pressure decreased with increasing of the processing temperature. Also the following thermal analysis were performed : Thermogravimetry (TG), Differential Scanning Calorimetry (DSC) and Dynamic-Mechanical Analysis (DMA). It was established that the processing temperature has a significant influence on the thermal stability and on the glass transition temperature of polymer while the flow temperature is slightly influenced by the processing temperature. Keywords: thermoplastic polyurethane (TPU), injection moulding, Thermogravimetry (TG), Differential Scanning Calorimetry (DSC) , Dynamic-Mechanical Analysis (DMA)

Abstract: This paper presents a study of the reactivity new carbosiloxane cyclic structures in anionic ring opening polymerization reactions in the presence of catalyst potassium siloxanolate. For this purpose, 2,2,5,5-tetramethyl-3,4-diphenyl-1-oxa-2,5-disilacyclo-pentane, 2,2,5,5-tetramethyl-3,3-diphenyl-1,4-dioxa-2,5-disilacyclopentane, 2,2,7,7-tetra-methyl-3,3,6,6-tetraphenyl-1-oxa-2,7-disilacycloheptane and bis-[1,4-bis-(dimethylsiloxanyl)-dihydronaphthalene] were used. The evolution of the polymerization reaction was observed through measurements of the reaction mixture inherent viscosity at various temperatures. The obtained results were processed in order to obtain the influence of the chemical structures on the processes conditions of development and kinetic parameters related to the transformation of the cycles to linear compounds. Keywords: cyclocarbosiloxanes, siloxanes, anionic polymerization, ring opening polymerization, organo-silicon compounds

Abstract: The more reliable values of the crystallization temperature were obtained from the non – isothermal DSC thermograms recorded at low cooling rate. The crystallization time was evaluated from the isothermal DSC thermogrames recorded at those temperatures at which the crystallization occurs. PP nucleated with Irgastab NA 21, has crystalline phase that contains the smallest spherulites, as compared to those nucleated with Irgastab NA 04 and Irgaclear DM. The incorporation of the nucleating / clarifying agents into the polymer matrix is homogeneous only if the melt processing conditions were well defined for each of them. A dependence on the molecular weight of the nucleated PP morphology was observed. The spherulite size decreases with the increase of the molecular weight. Keywords: crystalization, nucleation, polypropylene, nucleating agent, spherulite

Abstract: This article presents the experimental results regarding the glucose influence on poly (vinyl alcohol) (PVA) films. The results of infrared spectroscopy (FTIR), atomic force microscopy (AFM) and X-ray diffraction (XRD) measurements revealed the surface and structural changes induced by increasing the glucose concentration. Keywords: PVA, AFM, XRD, FTIR

Abstract: In this paper the 3D simulation model of typical porous polymer is presented. Porosity growth was caused by numerical handling of a spatial pores network. Although the algorithm has a good accuracy it is noticed that the final average pore sizes for simulated polymer networks are larger than the desired pore size. Keywords: polymer network, porosity, tissue engineering

Abstract: This paper is focused on the main static and dynamic characteristics in case of rubber elements designated to damp the vibrations transmitted to the surrounding buildings by means of the railway. Thus, the experimental methods performed on a stand having harmonic excitation in case of actual loading under dynamic regime both stationary and transient attaining the resonance point are presented. Based on this, the system dynamic parameters such as: dynamic rigidity, critical damping fraction, dissipation coefficient (hysteresis) can be determined. Aiming this the free damped vibration method and the controlled excitation method with monotone increasing variation for the excitation frequency have been used. In this way can comparatively be determined both the rigidity and the damping dynamic characteristics of the rubber for various manufacturing receipts taking into account the chemical composition as well as the manufacturing process. Finally, the paper presents experimental results obtained by our research institute ICECON Bucharest in cooperation with University “Dunãrea de Jos” of Galaþi during the works carried out for the tram rails in Bucharest, Romania. Keywords: elastomer, rigidity, damping, vibration, structural noise, antivibrating insulation

Abstract: Using the linearity of the term we will deduce a new formula for the calculus of the fracture strength for composites with randomly dispersed fibres. This formula will depend on the reinforcement volume fraction. Using the mean values for longitudinal and/or transversal modulus, with respect to the rotated reference system, we will obtain an original relation for the calculation of the elasticity modulus for composite plates with a randomly dispersed reinforcement. We preferred to write this relation in a similar manner to the one used for the failure strength, using the linearity related to . Experimental determinations were made for three sets of samples obtained from composite plates with various mass fractions of reinforcement, confirming thus the theoretical results obtained by the authors. Keywords: composite materials, fracture strength, longitudinal/transverse modulus

Abstract: One major disadvantage of polymeric composites is their low electrical conductivity. This is a trail-and-error study regarding PMC’s conductivity modification by filling the polymer matrix with various powders. Clay, CNT and Ferrites were used as fillers, Epoxy Epiphen RE 4020 with Epiphen DE 4020 as hardener was used as matrix and simple type fabric of alternate kevlar and carbon untwisted tows was used as reinforcement. The mechanical properties of a PMC are improved by using reinforcements so it is naturally to ask what is happening when a reinforced composite is formed with filled polymer matrix. Plate samples were formed and their electrical conductivity was evaluated. The filler’s concentration was considered and information was used in order to form the reinforced composite with the highest conductivity. Keywords: CNT, Ferrite, Clay, Epoxy, Fiber Fabric Reinforcement

Abstract: For the modeling and usual analysis of mechanical structures it is considered that the whole structure and its components accomplish one of the fundamental conditions of strength of materials – the condition of continuity and homogeneity. This paper presents some modeling techniques useful for the optimization of the numerical models in order to improve the structural response for impact applications. As some parts have to be damaged a material model capable of material failure must be used. The differences between the results obtained using a model without failure and a model with failure compared to the experiments were discussed. The second procedure is regarding the random distribution of the thickness properties of the elements for a selected area within the user specified tolerance. Procedures implemented in custom written code and the algorithms presented for the random distribution were presented. Keyword: material homogeneity, material model, random thickness, numerical simulation