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Search Results: 1 - 10 of 191574 matches for " D?unuzovi? Jasna "
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Development directions of packaging made from polymer materials
Jovanovi? Slobodan,DunuzoviJasna V.
Hemijska Industrija , 2011, DOI: 10.2298/hemind111018087j
Abstract: World packaging market achieves turnover of about $620 billion per year with one third of this amount being associated to packaging made from polymer materials. It is expected that this kind of packaging consumption will hold at least 3% of world packaging market share in the next five years and that it will surpass the consumption of all other materials used in the packaging production. This can be contributed to product quality, low production costs as well as significant investments made in the development of polymer materials, packaging technology and packaging. This paper presents some development directions for packaging made from polymer materials, such as: packaging in the protective atmosphere, the use of active and intelligent packaging, and the use of biopolymers and recycled polymers for packaging production that come into direct contact with the packed product.
Characterization of the commercial hyperbranched polyesters
DunuzoviJasna,Jovanovi? Slobodan,Lechner Manfred D.
Hemijska Industrija , 2010, DOI: 10.2298/hemind101014060d
Abstract: In this paper, properties of the commercially available Boltorn hydroxy-functional aliphatic hyperbranched polyesters of the second, third and fourth pseudo generation, were investigated. Beside that, samples of the third and fourth pseudo generation were fractionated using the precipitation fractionation method to obtain three fractions of each sample, which were also investigated in this paper. According to the results obtained by GPC analysis, molar mass and polydispersity of the investigated Boltorn hyperbranched polyesters increased with increase of the pseudo generation number. Value of the limiting viscosity number of the investigated samples, determined using the viscosity measurements of dilute solutions of these polymers in N-methyl-2-pyrrolidone, increased with increase of the pseudo generation number. On the other side, value of the limiting viscosity number of the fractions decreased from the first up to the third fraction. The same trend was also observed for the values of the hydrodynamic diameter of parent samples and their fractions, determined by dynamic light scattering using N-methyl-2-pyrrolidone as solvent. The thermal properties of the investigated Boltorn hyperbranched polyesters were determined by thermogravimetry in nitrogen atmosphere and it has been shown that thermal stability of these samples increased with increase of the pseudo generation number. End hydroxyl groups of the second and third pseudo generation samples were modified with β-alanine to obtain hyperbranched samples soluble in water. That was fully accomplished only for the Boltorn hyperbranched polyester of the second pseudo generation. On the other side, modified sample of the third pseudo generation was possible to dissolve in water only after adding small amount of the NaOH.
Influence of the way of synthesis of poly(methyl methacrylate) in the presence of surface modified TiO2 nanoparticles on the properties of obtained nanocomposites
Dunuzovi? Enis S.,Marinovi?-Cincovi? Milena T.,DunuzoviJasna V.,Jeremi? Katarina B.
Hemijska Industrija , 2010, DOI: 10.2298/hemind100923059d
Abstract: Incorporation of inorganic nanoparticles can significantly affect the properties of the polymer matrix. The properties of polymer nanocomposites depend on the type of incorporated nanoparticles, their size and shape, their concentration, and interactions with the polymer matrix. Homogeneity of polymer nanocomposites is influenced very much by the preparation method. In this study, TiO2 nanoparticles surface modified with 6-palmitate ascorbic acid (6-PAA) were incapsulated in poly(methyl methacrylate) (PMMA) by in situ radical polymerization of methyl methacrylate initiated by 2,2'-azobisisobutyronitrile (AIBN). The surface modification of the TiO2 nanoparticles was achieved by the formation of a charge transfer complex between TiO2 nanoparticles and 6-palmitate ascorbic acid. The radical polymerization of MMA in the presence of TiO2-PAA nanoparticles was conducted in solution (PMMA/TiO2-PAA-R), in bulk (PMMA/TiO2-PAA-M) or in suspension (PMMA/TiO2-PAA-S). The main purpose of this study was to investigate the influence of the preparation method on the molar masses and thermal properties of PMMA/TiO2-PAA nanocomposite. It was obtained that molar masses of PMMA extracted from the composites had smaller values compared to molar masses of pure PMMA synthesized in the same manner, which indicated that TiO2-PAA nanoparticles affected the reaction of termination. Thermal properties were investigated by DSC and TGA. The values of glass transition temperature, Tg, were influenced by the way the radical polymerization was conducted, even in the case of the pure PMMA. The Tg of composite samples was always smaller than the value of the corresponding PMMA sample and the smallest value was obtained for PMMA/TiO2-PAA-M since they contained the largest amount of low molar mass residue. The TGA results showed that thermal and thermooxidative stability of polymer composites obtained in solution and in suspension was better than for the pure PMMA obtained in the same way.
Surface plasmon resonance of Ag organosols: Experimental and theoretical investigations
Vukoje Ivana,Bo?ani? Du?an,DunuzoviJasna,Bogdanovi? Una
Hemijska Industrija , 2012, DOI: 10.2298/hemind120112028v
Abstract: The aim of this paper is to investigate and compare the changes in surface plasmon resonance (SPR) of silver (Ag) hydrosol and organosols obtained by experimental and theoretical approaches. Silver nanoparticles (Ag NPs) of 5 ± 1.5 nm in diameter were prepared in water by reduction of silver nitrate with sodium borohydride. Nanoparticles were subsequently transferred into different organic solvents (chloroform, hexane, toluene, 1,2-dichlorobenzene) using oleylamine as a transfer agent. These solvents were chosen because of the differences in their refractive indices. Using UV-Vis absorption spectrophotometry and transmission electron microscopy (TEM), we confirmed that there were no shape and size changes of the nanoparticles upon the transfer to the organic phase. The absorption spectra of the obtained Ag organosols showed only changes in the position of SPR band depending on dielectric property of the used solvent. To analyze these changes, absorption spectra were modelled using Mie theory for small spherical particles. The experimental and theoretical resonance values were compared with those predicted by Drude model and its limitations in the analysis of absorption behavior of Ag NPs in organic solvents were briefly discussed.
Synthesis and swelling behavior of polyurethane networks based on hyperbranched polymer
DunuzoviJasna V.,Pergal Marija V.,Jovanovi? Slobodan,Vodnik Vesna V.
Hemijska Industrija , 2011, DOI: 10.2298/hemind110902071d
Abstract: A series of six polyurethane (PU) networks was synthesized from BoltornR hydroxy-functional hyperbranched polyester (HBP) of the second pseudo generation as a crosslinking agent, α,ω- dihydroxy-(ethylene oxide-poly(dimethylsiloxane)-ethylene oxide) (EO-PDMS-EO) and 4,4’- methylenediphenyl diisocyanate, by a two-step polymerization in solution. Each sample of the prepared PUs had different EO-PDMS-EO content. The chemical structure of the synthesized networks was analyzed by FTIR spectroscopy. The influence of the EO-PDMS-EO content and type of the solvent on the swelling behavior of the PUs in 2-propanol and toluene was investigated. During the swelling measurements certain amount of sol fractions was extracted from the PUs by solvents. According to the 1H NMR results, sol fractions are mainly composed of the soluble hyperbranched PU, formed during the polymerization by partial modification of the end hydroxyl groups of HBP with NCO-terminated prepolymer synthesized in the first step of the reaction. Chains of the so reacted prepolymer can then fold back and form cyclic products by reaction of the free -NCO group from the NCO-terminated prepolymer with free -OH group of HBP. As the EO-PDMS-EO content increases the amount of the sol fractions and swelling degree also increased, indicating that networks with lower EO-PDMS-EO content are more crosslinked and have higher solvent resistance.
Investigation of the morphology and surface properties of crosslinked poly(urethane-ester-siloxane)s
DunuzoviJasna V.,Pergal Marija V.,Vodnik Vesna V.,?pírková Milena
Hemijska Industrija , 2012, DOI: 10.2298/hemind121004101d
Abstract: Two series of crosslinked poly(urethane-ester-siloxane)s were synthesized from α,ω-dihydroxy-(ethylene oxide-poly(dimethylsiloxane)-ethylene oxide) (EO-PDMS-EO), 4,4’-methylenediphenyl diisocyanate and Boltorn hyperbranched polyesters of the second and third pseudo generation, by a two-step polymerization in solution. The effect of the EO-PDMS-EO content and functionality of the applied crosslinking agent on the morphology and surface properties of the prepared poly(urethane-ester-siloxane)s was investigated by FTIR spectroscopy, small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and water absorption measurement. Different techniques (FTIR peak deconvolution, SAXS and AFM) revealed that decrease of the crosslinking agent functionality and EO-PDMS-EO content promotes microphase separation in the synthesized poly(urethane-ester-siloxane)s. SEM analysis and water absorption experiments showed that due to the hydrophobic character of EO-PDMS-EO and its ability to migrate to the surface of poly(urethane-ester-siloxane)s, samples synthesized with higher EO-PDMS-EO content and crosslinking agent of lower functionality have more hydrophobic surface and better waterproof performances. The obtained results indicate that the synthesis of poly(urethane-ester-siloxane)s based on EO-PDMS-EO and Boltorn hyperbranched polyesters leads to the creation of networks with interesting morphological and surface properties, which can be easily tailored by changing the content of EO-PDMS-EO segment or functionality of hyperbranched polyester.
Poly(urethane-siloxane)s based on hyperbranched polyester as crosslinking agent: Synthesis and characterization
Pergal Marija V.,DunuzoviJasna V.,Ostoji? Sanja,Pergal Miodrag M.
Journal of the Serbian Chemical Society , 2012, DOI: 10.2298/jsc111013006p
Abstract: A series of novel polyurethane crosslinked structures (PUs) was prepared from α,ω-dihydroxy-(ethylene oxide-poly(dimethylsiloxane)-ethylene oxide) (EO-PDMS-EO), 4,4’-methylenediphenyl diisocyanate and Boltorn hyperbranched polyester of the third pseudo generation. The hydroxyfunctional hyperbranched aliphatic polyester with 26 end groups was used as crosslinking agent. In order to improve the compatibility of all reactants during the synthesis, PU samples were prepared by a step-growth polymerization in two stages in solution. The soft EO-PDMS-EO segment content was varied in the range from 15 to 40 wt.%. The influence of the EO-PDMS-EO content on the swelling behavior, crosslinking density, hardness, thermal and surface properties of the synthesized PUs was investigated. The structure of the synthesized polyurethanes was confirmed by the presence of specific bands in Fourier transform infrared spectra. Swelling studies were carried out to determine the crosslinking density and polyurethane networks with lower EOPDMS- EO content revealed higher crosslinking density. The glass transition temperature of the synthesized PUs, determined by differential scanning calorimetry, slightly increased from 50 to 58°C by decreasing EO-PDMS-EO content as a consequence of higher crosslinking density of samples. The increase of EO-PDMS-EO content leads to the better thermal stability, as it was confirmed by the value of the starting temperature of thermal degradation. The surface of the polyurethane networks became more hydrophobic with increasing EO-PDMS-EO content. The surface morphology of synthesized polyurethanes was analyzed by scanning electron microscopy.
New Hybrid Properties of TiO2 Nanoparticles Surface Modified With Catecholate Type Ligands
Jankovi? Ivana,?aponji? Zoran,Dunuzovi? Enis,Nedeljkovi? Jovan
Nanoscale Research Letters , 2009,
Abstract: Surface modification of nanocrystalline TiO2 particles (45 ) with bidentate benzene derivatives (catechol, pyrogallol, and gallic acid) was found to alter optical properties of nanoparticles. The formation of the inner-sphere charge–transfer complexes results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites. The binding structures were investigated by using FTIR spectroscopy. The investigated ligands have the optimal geometry for chelating surface Ti atoms, resulting in ring coordination complexes (catecholate type of binuclear bidentate binding–bridging) thus restoring in six-coordinated octahedral geometry of surface Ti atoms. From the Benesi–Hildebrand plot, the stability constants at pH 2 of the order 103 M 1 have been determined.
Initiation of MMA polymerization by iniferters based on dithiocarbamates
Jovanovi? Slobodan M.,Nastasovi? Aleksandra B.,Dunuzovi? Enis S.,Jeremi? Katarina B.
Hemijska Industrija , 2005, DOI: 10.2298/hemind0512311j
Abstract: Twelve modified dithiocarbamates and a thiuramdisulfide used for the initiation of methyl methacrylate (MMA) polymerization were synthesized in this study. The polymerization of MMA was followed by determine the yield and molar mass of the obtained PMMA as a function of polymerization time. Four of the synthesized dithiocarbamates S-benzyl-N,N-dibenzyldithiocarbamate, S-allyl-N,N-dibenzyldithiocarbamate S-benzyl-N,N-diisobutyldithiocarbamate and S-benzoyl-N,N-diisobutyldithiocarbamate, as well as N,N,N',N'-tetrabenzylthiuramdisulfide acted as iniferters. They were active as the initiators of the photo and/or thermally initiated radical polymerization of MMA in bulk and inert solvents (benzene and toluene). S Benzyl - N,N - dibenzyldithiocarbamate can be successfully used for the initiation of MMA polymerization in a polar solvent such as dimethylacetamide.
ENFERMERíA BASADA EN LA EVIDENCIA Y FORMACIóN PROFESIONAL
Eterovic Díaz,Claudia; Stiepovich Bertoni,Jasna;
Ciencia y enfermería , 2010, DOI: 10.4067/S0717-95532010000300002
Abstract: consensus exists in the value evidence-based nursing (ebn) offers to professional nursing practice, in the systematic search for answers using a reflective and interpretative approach, and in building on studies that convert research findings into nursing practice. this article proposes didactic strategies that allow the development of competency in reflective critical thinking and information searching in professional nursing education curricula which would result in evidence-based nursing practice, as an ongoing process, in at attempt to improve the quality of the health care offered.
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