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Flexible multiferroic composite films are perspective materials for sensors, actuators and similar components of wearable and stretchable devices. Here we present the study of functional properties of flexible composites prepared by embedding nickel zinc ferrite and barium titanate powder into polyvinylidene fluoride (PVDF) polymer optimizing the ratio of polymer and fillers to get the best flexibility and functionality. ATR-FTIR analysis revealed that hot pressing of the flexible films caused a transformation of about 38% of the electro-inactive PVDF α phase into electrically active β and γ phases. Broadband dielectric spectroscopy revealed two relaxation processes responsible for PVDF and space charge relaxations. Activation energies of both processes and the freezing temperature of PVDF to the glass phase were estimated for all films. Ferroelectric measurements have shown unsaturated hysteresis loops for all samples, although the clear dependence of the amount of the electrically active phase on polarization values of composites is visible.

The scope of the present study was to prepare fully bio-based unsaturated polyester resins (UPRs) with comparable properties to the commercial formulations. The focus was set on the determination of the optimal prepolymer formulation using the same set of diacids (itaconic and succinic acid) and different diols (propylene glycol, isosorbide and neopentyl glycol) or its equimolar mixtures, keeping the fixed molar ratio of 1:1:2.1 in all feed compositions. Instead of commonly used styrene, bio-based dimethyl itaconate was used as a reactive diluent (RD). The rheology of the obtained resins was studied in detail. The effect of the used diol on structural (FTIR), thermal (DSC), thermomechanical (DMA), and mechanical (tensile) properties was explained. The properties of UPRs were found to be highly dependent on the diol used in the prepolymer formulation. The UPR with an equimolar ratio of propylene glycol and neopentyl glycol was shown to be the most promising candidate to compete with the commercial petroleum-based resins.

Multiferroic composites with general formula Ba(Ti0.95Zr0.05)O3 – Ni0.7Zn0.3Fe2O4, Ba(Ti0.95Zr0.05)O3 – CoFe2O4, Ba(Ti0.95Zr0.05)O3 – Ni0.7Cu0.01Sm0.05Zn0.29Fe1.95O4, (BTZr(95–5) – NZF, BTZr(95–5) – CF, BTZr(95–5) – NCuSmZF) were prepared by mixing chemically obtained different types of ferrites and BTZ(95–5) powders in the planetary mill for 24 h. The optimization of sintering process was performed and powders were pressed and sintered at 1300 °C for obtained composites samples. From the X-ray analysis for single phase and composites ceramics the formation of crystallized structure of ferrites and barium zirconium titanate can be noticed. SEM analyses indicated the formation of two types nanosized grains, polygonal ferromagnetic and rounded ferroelectric grains. The electrical properties of these materials were investigated using impedance spectroscopy and analysis of ferroelectric measurements. Impedance analysis of all investigated samples has shown different relaxation processes that originated from the grain and grain boundary contributions. The results of polarization vs. electric field measurements have shown the influence of magnetic phase type and its concentration on the ferroelectric properties of the composites. Due to high conductivity of ferrite phases and presence of interfacial polarization, the shapes of these curves differed from the conventional ferroelectric materials.

Composites based on barium titanate and nickel zinc ferrite doped with cooper and samarium were prepared by a mixing method. The formation of barium titanate tetragonal crystal structure and nickel zinc ferrite cubic spinel structure was identified. Polygonal grains were formed in all three types of ceramics. Due to the very high conductivity of ferrite phase in the materials the ferroelectric hysteresis loops were roundish and not typical for classical ferroelectric material. The break down field was found to be similar for all compositions. Leakage current measurements have shown the existence of different types of conductivity mechanisms in each material. The impedance analysis suggested a bit stronger impact of grain boundaries on total conductivity of the composites and the mechanism of polaronic conduction of two types. The magnetization of the composites is lower than for the pure ferrite phase and corresponds to the weight fraction of the ferrite phase. The soft magnetic nature of these composites might be very useful for development of multifunctional devices which will be able to switch the magnetization with small external magnetic field. Humidity sensing properties of the prepared ceramics were also investigated.

To investigate the effect of synthesis procedure and sintering temperature on the functional properties of perovskite/spinel ceramics, BaTiO3/CoFe2O4 composites were prepared by thermal decomposition, coprecipitation, and microemulsion method, and sintered at 1150?C and 1300?C. The phase composition and morphology of as-prepared powders as well as sintered ceramics were thoroughly examined by X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) coupled with electron dispersive spectroscopy (EDS). The dielectric and ferroelectric measurements were performed in detail. Generally, the samples sintered at 1300?C had better performances than those sintered at 1150?C. The composite synthesized by thermal decomposition and sintered at 1300?C stands out among other prepared BaTiO3/CoFe2O4 ceramics, owing to high stability in the wide frequency range and low leakage currents. The obtained results indicate that such composite might be successfully applied as a functional multiferroic.

BaTiO3 nanopowders doped with La and co-doped with La/Mn were prepared by auto-combustion and Pechini methods, respectively. The influence of the synthesis methods, dopants and sintering temperature on the BaTiO3 structure and its potential to be used as humidity and/or H2 gas sensor were studied. The optimization of all process parameters was performed to obtain adequate microstructure for the development of good sensor properties. The difference in the grain size between the La-doped and La/Mn co-doped samples and the formation of different types of defect structures in these ceramics were found to be significant for the desired electrical and ferroelectric properties. The La-doped ceramics with a pseudo-cubic structure showed the highest potential for gas sensors. The materials obtained by the Pechini method had a tetragonal structure and showed the best response, i.e., the change in electrical resistivity by four orders of magnitude in the humid atmosphere.

The ferroelectric and magnetic properties of four-layered Aurivillius Bi5Ti3FeO15 (BFT) compounds via partial substitution of Bi3+ with Y3+ and Fe3+ with Co2+ (according to formula: Bi5 − xYxTi3FeO15, x = 0.1, 0.2, 0.3; Bi5Ti3Fe1 − yCoyO15, y = 0.1, 0.3, 0.5) were investigated. Polycrystalline ceramics of Co and Y substituted BFT were prepared by conventional solid-state reaction. Crystal structure and phase purity were confirmed via X-ray diffraction. Raman spectral signatures indicate that Y replaces Bi ions in the pseudo-perovskite layers and Co replaces Fe ions in the octahedral sites. SEM micrographs show a decrease in grain size for both chemically modified samples when compared to plate-like morphology for pure BFT with dimensions ranging from 3–5 µm in length and a thickness of ~ 0.5 µm. The decrease in grain size is more pronounced in Co substituted samples with plate-like grain dimensions of 1 µm in length and 0.1 µm in thickness. Ferroelectric measurements show unsaturated leaky hysteresis loops in both chemically modified samples until the maximum applied electric field. Magnetic measurements confirm the paramagnetic nature of pure and Y substituted BFT ceramics while Co substituted BFT ceramics exhibit a typical ferromagnetic M-H loop. The largest remanent magnetization value of 0.084 emu/g at room temperature is recorded for the Co2+ substituted sample with x = 0.30.

Multiferroic composite materials based on antimony doped barium titanate/nickel ferrite were prepared by a mixing route. In order to obtain fine grained microstructure composite materials, pure constituent phases were prepared via chemical methods. The optimization of processing parameters has been made in order to reduce the chemical reactions at the interfaces between ferroelectric-ferrite phases. XRD data confirmed the presence of both barium titanate and nickel ferrite phases in the ceramic samples. The resistivity data obtained from impedance as well as calculated activation energies indicated the grain boundary contribution as a more influential effect in the total resistivity of ceramics. Dielectric permittivity enhancement in comparison with composites prepared from pure barium titanate was noticed. Well defined hysteresis loops have shown the changes of properties induced by the modification of the barium titanate phase with Sb doping and due to the co-existence of two different phases in the materials. The comparative study of magnetic properties of obtained composite materials was presented. The results on the magnetodielectric properties are understood in terms of the stress induced variations in the polarization and dielectric permittivity.

Comparative study of different PZT-based composite materials ((x)PbZr 0.52 Ti 0.48 O 3 + (1-x)CoFe 2 O 4 and (x)PbZr 0.52 Ti 0.48 O 3 +(1-x)Ni 0.7 Zn 0.3 Fe 2 O 4 (x = 0.8 and 0.9)) is presented in the frame of structural, dielectric, ferroelectric and magnetic properties. PZT and NZF/CF powders were synthesized by auto combustion technique. The composites were synthesized by mixing the appropriate amount of individual phases using conventional sintering. XRD data indicated the formation of well crystallized structure of PZT and NZF/CF, without the presence of undesirable phases. SEM micrographs revealed a uniform grain distribution of both, ferroelectric and ferromagnetic phases. Non-saturated hysteresis loops are evident in all samples due to the existence of non-ferroelectric ferrite phase. All the samples exhibit typical ferromagnetic hysteresis loop, indicating the presence of the order magnetic structure. Dielectric investigations revealed that ferrites are the main source of charge carriers, which must be of electronic origin. The activation energy of effective electrical resistivity is heavily influenced by the ferroelectric phase.

Di-phase ceramic composites, with general formula xNi 0.7 Zn 0.3 Fe 2 O 4 – (1-x)BaTiO 3 (x = 0.9, 0.7, 0.5, 0.3, 0.1), were prepared by a mixing method. X-ray analysis, for powder and ceramics, indicated the formation of ferrite and barium titanate phases without the presence of the impurities. SEM analysis indicated that the composite morphology contained two types of grains, polygonal and rounded. Homogeneous microstructure and the smallest grain size were obtained in ceramics with 70% of barium titanate. The electrical properties of these materials were investigated using impedance spectroscopy, dielectric and ferroelectric measurements. The NZF-BT(30-70) composite has shown better electrical properties in comparison to other investigated ceramics, confirmed by dielectric and ferroelectric data analysis. Saturation magnetization and coercive field decreased with the increase of the content of ferroelectric phase.

The idea of this work is finding the way to efficiently and safely use mechanical energy released in small quantities around us to power up small-scale electronic devices used in everyday life. To this purpose, flexible lead-free piezoelectric composite films were prepared by hot pressing. Different amounts (30, 35 and 40 vol%) of lead-free piezoelectric material bismuth sodium titanate-barium titanate were embedded in the matrix of polyvinylidene fluoride under carefully optimized conditions of temperature and pressure, obtaining flexible films with quite homogeneous distribution of piezo-active filler. ATR-FTIR analysis revealed that hot pressing the flexible films caused a transformation of electro-inactive PVDF α-phase into electro-active β and γ phases. Dielectric measurements showed an increase of the permittivity up to 80 with the active phase increasing. Anelastic measurements showed that the elastic modulus increases as well with the fraction of active ceramic phase. Lastly, obtained flexible polymer-composites demonstrated notable properties both for energy storage and energy harvesting application, showing up to 74% of energy storage efficiency and, from testing of the force impact, up to 9 V and ~ 80 μW of output voltage and power.

Surface modification of titanium dioxide nanoparticles (TiO2 NPs) with the biologically active molecule pyridoxine hydrochloride (vitamin B6) was found to alter the optical properties. Microstructural characterization involving transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis revealed that the anatase TiO2 NPs had a narrow size distribution with an average diameter of 45 Å. The absorption onset of the surface-modified TiO2 samples was red-shifted by about 0.4 eV compared to the unmodified particles. The mode of binding between vitamin B6 and the surface Ti atoms was investigated by Fourier transform infrared spectroscopy (FTIR). From the Benesi– Hildebrand plot, the stability constant of the surface complex was found to be of the order 102 M-1. The experimental findings were supported by detailed quantum chemical calculations based on the density functional theory (DFT). Agreement was found between the experimentally measured absorption spectra of the TiO2 NPs surface-modified with vitamin B6 and the theoretically calculated electronic excitation spectra of the corresponding model system. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 172062 and Grant no. 45020]

Conventional solid-state method was used to prepare powders of pure and barium titanate (BT) doped with different concentration of samarium. Influence of samarium addition on the structure modification, grain growth inhibition and microstructure development was studied. Dielectric properties of doped samples were significantly modified. With doping, a diffuse kind of ferro-para phase transition was induced, phase transitions positions were shifted and dielectric permittivity values were lowered in comparison with pure barium titanate. Detailed impedance and modulus data analysis were presented. The impedance complex plane showed two semicircular arcs for pure BT and one single depressed semicircular arc for all doped ceramics. Different electro-active regions in the modulus plane plots were also distinguish. The comparison between impedance and modulus scaling behavior presented the localized movement of charge carriers in the pure barium titanate and both, short and long range relaxations in the ceramics doped with 0.05 mol% of Sm. P-E hysteresis loops have shown the dilution of ferroelectric properties with Sm doping.

The effect of tungsten (W 6+ ) doping on modification of the structure, dielectric, ferroelectric and electrical properties of BaBi 4 Ti 4-x W x O 15 (BBTWx, x = 0, 0.03, 0.05 and 0.07) was investigated. The ceramic samples were synthesized by the conventional solid state reaction method. XRD data indicated the formation of single-phase layered crystalline structure that confirmed orthorhombic structure type of all compositions with space group A2 1 am . SEM micrographs suggest that the grain size slightly decreases with W doping. The temperature dependent dielectric study revealed that the dielectric constant decreases with W doping while transition temperature slightly increases. Influence of tungsten on relaxor behavior and diffuseness of phase transition is also discussed. Effect of W doping on the dielectric and electrical properties were investigated in terms of ion doping and defect mechanism. The ferroelectric properties were studied by P-E hysteresis loop and it was observed that the remanent polarization increases with a small level of W doping.

Made available in DSpace on 2018-12-11T17:31:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-12-01 Ministarstvo Prosvete, Nauke i Tehnološkog Razvoja Nickel zinc ferrite (NZF) and barium titanate (BT) were prepared by auto-combustion synthesis as an effective, simple and rapid method. Multiferroic composites with the general formula yNi1−xZnxFe2O4−(1−y)BT (x=0.3, 0.5, 0.7, y=0.5) were prepared by mixing NZF and BT powders in a liquid medium in the ball mill. The FEG micrographs indicated the primary particle size less than 100 nm for both, barium titanate and nickel zinc ferrite phases. X-ray analysis and Raman spectroscopy indicated the formation of well crystallized structure of NZF and BT phase in the composite powders and ceramics, with a small contribution of the secondary phase. The homogenous phase distribution in obtained composites was also confirmed. Impedance spectroscopy measurements were carried out in order to investigate the electrical resistivity of materials, showing that grain boundaries have greater impact on the total resistivity than grains. Saturation magnetization and remnant magnetization continuously decrease with barium titanate phase increase. Institute for Multidisciplinary Research University of Belgrade Institute of Physics University of Belgrade UNESP Faculty for Engineering UNESP Institute for Chemistry UNESP Faculty for Engineering UNESP Institute for Chemistry Ministarstvo Prosvete, Nauke i Tehnološkog Razvoja: III 45021

The composite materials mixed with soft polymers present a new class of materials with specific electric, magnetic, and mechanical properties. Organic materials used as a polymer matrix in these composites possess low electrical conductivity, high chemical stability, and low processing temperature. Among the most common polymer matrices, PVDF and P(VDF-TrFE) are marked as an ideal candidates due to their piezoelectric and ferroelectric features. Review of selected examples of complex composites based on ferroics or multiferroics embedded in polymeric matrix is presented.

Metal oxides are a subject of interest because of their optical, electronic, and magnetic properties suitable for a variety of applications. Among the various metal oxides, magnetic metal oxides occupy an important place due to the numerous possibilities of their usage. Until 1740, the only useful permanent magnets known to man were lodestones largely composed of impure magnetite, the black spinel-structure oxide Fe3O4 with a ferrimagnetic arrangement of magnetic moments. The other common rock-forming iron oxide is hematite, the reddish corundum-structure sesquioxide α-Fe2O3, which is antiferromagnetic with magnetization about 200 times weaker than magnetite. The first more serious study of magnetism was made by Gilbert, who published his famous classic book, On the Magnet. But for a long time after that there were no discoveries of any fundamental importance, although many practical improvements in the manufacture of magnets appeared. In 1820 Oersted made the great discovery that an electric current produces a magnetic property, opening the field of electromagnets.

Modified Pechini process was used to prepare nanopowders of barium titanate (BT) co-doped with different concentrations of niobium and manganese. Influence of dopants on the grain growth inhibition and microstructure development was analyzed. The addition of dopants significantly influenced the dielectric properties modification. The obtained ɛ–T curves of all ceramics have the shape of typical ferroelectric material but the increase of dielectric permittivity value and movement of phase transitions with different dopant concentrations were clearly noticed. Grain and grain boundary resistivities for all co-doped ceramics were extracted from detailed impedance analysis and the grain boundary effect was indicated as a dominant effect in the total conduction of the materials. The well-defined and saturated P–E hysteresis loops of the ceramics confirmed the existence of ferroelectric properties.

Spherical TiO2 particles of different size were dispersed in alkyd resin based on soybean oil. Four samples of TiO2 particles were used, three commercial and one obtained by acid catalyzed hydrolysis of titanium tetraisopropoxide. The size of the synthesized nanoparticles was determined by transmission electron microscopy. Surface modification of TiO2 nanoparticles was performed with propyl gallate and lauryl gallate. The influence of the size of TiO2 nanoparticles, their concentration and type of the surface modification on the rheological properties of alkyd resin was investigated. The obtained results have shown that the viscosity of the prepared dispersions was higher than the viscosity of the pure resin, increases with decreasing particle diameter and decreases with frequency increase. Surface modified particles showed higher influence on the viscosity of alkyd resin than unmodified, because their hydrodynamic volume is higher due to the presence of the adsorbed gallates, leading to the increase of effective volume fraction of particles in dispersion. For the lowest TiO2 concentration, the viscosity was higher for the sample modified with lauryl gallate, due to the higher thickness of the adsorbed layer. The increase of concentration, because of less dispersion stability of the particles modified with propyl gallate, leads to particle agglomeration. The presence of agglomerates, which was confirmed by a change in the slope of the functional dependence of storage modulus on loss modulus, leads to a rapid increase in viscosity. Sferne čestice TiO2 različitih veličina dispergovane su u alkidnoj smoli. Površinska modifikacija nanočestica TiO2 izvedena je propil galatom i lauril galatom. Ispitivan je uticaj veličine nanočestica TiO2, koncentracije, kao i vrste površinske modifikacije na reološka svojstva alkidne smole. Dobijeno je da je viskoznost pripremljenih disperzija veća od viskoznosti čiste smole, da raste sa smanjenjem prečnika čestica i opada sa povećanjem frekvencije. Površinski modifikovane čestice imaju veći uticaj na viskoznost alkidne smole nego nemodifikovane zbog povećanja efektivnog zapreminskog udela čestica u disperziji. Za najmanju koncentraciju TiO2 viskoznost je veća kada je modifikacija izvršena lauril galatom, dok sa povećanjem koncentracije, zbog manje disperzione stabilnosti čestica modifikovanih propil galatom, dolazi do njihove aglomerizacije i naglog povećanja viskoznosti.

The poor stability and tendency to agglomerate of unfunctionalized nano-SiO2 in the presence of ionic species presents a challenge for preparing poly(methacrylic acid)/nano-SiO2 nanocomposite (NC) hydrogels with desired strength and swelling capability. We proposed a facile and eco-friendly method for the preparation of PMAA/SiO2 NC hydrogels using unfunctionalized silica nanoparticles (NPs) in the form of a suspension. SEM and TEM analyses showed that the NP distribution in the polymer matrix highly depended on the particle concentration. At lower concentrations (up to 13.9 wt %), the NPs were uniformly dispersed as single nanoparticles. With an increase in NP concentration, homogeneously dispersed nanoscale aggregates were formed, while a further increase in the silica concentration led to the formation of homogeneous structures consisting of mutually interacting nanosilica particles coated with PMAA. Swelling experiments confirmed that the silica NPs behaved as adhesive fillers that interacted with PMAA chains, causing the formation of a thin polymer layer strongly adsorbed at the particle interface. The thicknesses of the adsorbed polymer layer, as well as the swelling kinetic parameters, were strongly influenced by nanoparticle size and concentration. Combining nanosilica and PMAA in the form of a soft hydrogel network provided stabilization of the NPs and ensured better mechanical properties of the obtained NC hydrogels compared to pure polymer matrix. The optimal loadings, necessary to ensure the most improved dynamical-mechanical properties, were found in the case of the formation of homogeneously dispersed, nanosized silica aggregates in a PMAA matrix.

Multiferroic composites with the general formula x BaTiO 3 –(1− x ) NiFe 2 O 4 ( x =0.5, 0.7, 0.8) were prepared by mixing chemically obtained nickel ferrite and barium titanate powders. Optimum processing parameters for a reduction of chemical reactions at the interfaces between ferroelectric-ferrite phases were found. The presence of the nickel ferrite and barium titanate single phases was detected by X-ray measurements. Good quality of the homogenized ceramics containing both phases was confirmed by use of scanning electron microscopy. Dielectric measurements showed the superposition of the multiple conductivity mechanisms responsible for the dielectric dispersion at frequencies up to 1 MHz. Calculated activation energies for DC conductivity showed the contribution of oxygen vacancies and Maxwell-Wagner related phenomena. Magnetic measurements of the composite materials were performed showing the coercivity increase and saturation of the magnetization moment decrease with the increase of barium titanate content.

Novel soy alkyd-based nanocomposites (NCs) were prepared using TiO2 nanoparticles (NPs) surface modified with different gallates, and for the first time with imine obtained from 3,4-dihydroxybenzaldehyde and oleylamine (DHBAOA). Unmodified and surface modified anatase TiO2 NPs were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible (UV-Vis) spectroscopy, while the amount of adsorbed ligands was calculated from thermogravimetric analysis (TGA) results. Surface modification of TiO2 NPs was confirmed by FTIR and UV-Vis spectra. The influence of the TiO2 surface modification on the dispersion of TiO2 NPs in alkyd resin, thermal, barrier and mechanical properties and chemical resistance of alkyd resin/ TiO2 NC coatings was investigated. The obtained results revealed that glass transition temperature of all investigated NCs is lower than for pure resin, that the presence of TiO2 NPs surface modified with gallates had no significant influence on the thermooxidative stability of alkyd resin, while TiO2-DHBAOA NPs slightly improved alkyd resin thermooxidative stability. Also, the presence of surface modified TiO2 NPs improved barrier properties, increased stress and strain at break and hardness and chemical resistance and decreased modulus of elasticity and abrasion resistance of alkyd resin.

Influences of the vinyl modified nanosilica Aerosil (R) 380, i.e., vinyl and methacryloyl silane coupling agent and linseed oil fatty acids (BD) reactive residues, on the mechanical properties of the unsaturated polyester resins (UPes) based nanocomposites, was studied. The polycondensation of maleic anhydride and products of poly(ethylene terephthalate) (PET) depolymerization with propylene glycol, with and without separation of ethylene glycol, yields UPe1 and UPe2 resin, respectively. The hydroxyl terminated PET depolymerization products (glycolyzates) and UPes were characterized by acid and hydroxyl values, Fourier Transform Infrared (FTIR) and nuclear magneti resonance (NMR) spectroscopies. Transmission electron microscopy (TEM) confirmed that silica nanoparticles formed domains of aggregates in the polymer matrix. An increase from 195 to 247% of stress at break (sigma(b)), and from 109 to 131% of impact strength (sigma(i)) of UPes based nanocomposites was obtained for 1 wt% addition of vinyl modified silica. Flexural strength (sigma(f)) increase from 106 to 156% for both UPes based nanocomposites with 1 wt% addition of BD modified silica. Cross-linking density (nu), storage modulus (G'), tan delta and T-g of the nanocomposite were determined from the dynamic mechanical testing and discussed in relation to the structure of silica modification.

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 a crosslinking agent. In order to improve the compatibility of all the reactants during the synthesis, the PU samples were prepared by two-stage, step-growth polymerization in solution. The content of the soft EO-PDMS-EO segments was varied in the range from 15 to 40 wt. %. The influence of the EO-PDMS-EO content on the swelling behavior, crosslink density, hardness, and the 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 the Fourier transform infrared spectra. Swelling studies were performed to determine the crosslink density and polyurethane networks with lower EO-PDMS-EO contents had higher crosslink densities. The glass transition temperature of the synthesized PUs, determined by differential scanning calorimetry, slightly increased from 50 to 58°C on decreasing the EO-PDMS-EO content because of the higher crosslink density of the samples. Increasing the EO-PDMS-EO content led to better thermal stability, as was evidenced by the onset temperature of weight loss. 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. U ovom radu prikazana je sinteza, struktura i neka svojstva novih umreženih poliuretana pripremljenih polazeći od α,ω-dihidroksi-(etilenoksid-poli(dimetilsiloksan)-etilenoksid) pretpolimera (EO-PDMS-EO), 4,4'-metilendifenildiizocijanata i Boltorn® hiperrazgranatog poliestra treće pseudo-generacije. Hiperrazgranati hidroksi funkcionalni alifatski poliestar sa 26 krajnjih grupa služio je kao umrežavajući agens pri sintezi poliuretana. U cilju poboljšanja kompatibilnosti reaktanata tokom sinteze, poliuretani su sintetisani dvostepenom polimerizacijom u rastvoru. Sadržaj mekog EO-PDMS-EO segmenta variran je u opsegu od 15 do 40 mas. %. Ispitan je uticaj EO-PDMS-EO sadržaja na ponašanje pri bubrenju, gustinu umrežavanja, tvrdoću, termička i površinska svojstva sintetisanih poliuretana. Struktura sintetisanih poliuretana potvrđena je FTIR spektroskopijom. Ponašanje pri bubrenju je ispitivano kako bi se odredila gustina umrežavanja i pokazano je da poliuretanske mreže sa nižim EO-PDMS-EO sadržajem imaju veću gustinu umrežavanja. Rezultati diferencijalne skenirajuće kalorimetrije pokazali su povećanje temperature ostakljivanja poliuretana od 50 do 58°C sa smanjenjem EO-PDMS-EO sadržaja kao posledicu veće gustine umreženosti uzoraka. Sintetisani poliuretani sa većim sadržajem EO-PDMS-EO segmenata pokazuju bolju termičku stabilnost, što je potvrđeno porastom početne temperature degradacije, određene TG analizom. Hidrofobnost površine poliuretana je rasla sa povećanjem sadržaja EO-PDMS-EO u odgovarajućem uzorku. Površinska morfologija sintetisanih poliuretana je analizirana skenirajućom elektronskom mikroskopijom.

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.

The surface of anatase TiO2 nanoparticles, obtained by the controlled hydrolysis of titanium tetrachloride, was modified by 6-palmitate ascorbic acid. The surface modified TiO2 nanoparticles were dispersed in methyl methacrylate and mixed with a appropriate amount of poly(methyl methacrylate) to obtain a syrup. The nano-composite sheets were made by bulk polymerization of the syrup in a glass sandwich cell using 2,2-azobisisobutyronitrile as initiator. The molar masses and molar mass distributions of synthesized poly(methyl methacrylate) samples were determined by gel permeation chromatography. The content of unreacted double bonds in synthesized samples was determined by H-1 NMR spectroscopy. The influence of TiO2 nanoparticles on the thermal stability of the poly(methyl methacrylate) matrix was investigated using thermogravimetric analysis and differential scanning calorimetry. The synthesized samples of poly(methyl methacrylate) have different molar mass and polydispersity depending on the content of the surface modified TiO2 nanoparticles. The values of glass transition temperature of so prepared nanocomposite samples were lower than for pure poly(methyl methacrylate), while the glass transition temperature of samples preheated in inert atmosphere was very similar to the glass transition temperature of pure poly(methyl methacrylate). The thermal stability of nanocomposite samples in nitrogen and air was different from thermal stability of pure poly(methyl methacrylate). POLYM. COMPOS., 30:737-742, 2009. (C) 2008 Society of Plastics Engineers

Urethane acrylate resins based on partially modified aliphatic hyperbranched polyesters (HBP) have been synthesized. HBP of the second and the third generation were synthesized from 2,2-bis(hydroxymethyl)propionic acid and di-trimethylol propane. The modification of certain amount of OH end-groups was carried out with soybean fatty acids. The urethane acrylates with different degrees of acrylation have been obtained by reaction of partially modified HBP and different amounts of NCO adduct which had been previously obtained by reaction of equimolar amounts of isophorone diisocyanate and 2-hydroxyethyl acrylate. The synthesized samples were characterized by FT-IR, 1 H and 13 C NMR and GPC. The rheological properties of uncured samples and mechanical and thermal properties of UV cured urethane acrylates diluted with 20 wt.% hexanediol diacrylate were examined. The modification of OH end-groups with soybean fatty acids causes a rapid decrease in viscosity of HBP. The examined properties of urethane acrylates depend on the degree of acrylation. After irradiating, the additional cross-linking, which is caused by reaction of double bonds from unsaturated fatty acids, has also important effect on the properties of cured samples.

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 encapsulated 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. Predmet ovog rada je dobijanje i karakterizacija nanokompozita kod kojih polimernu matricu čini poli(metil metakrilat) (PMMA), a kao neorgansko punilo nanočestice titan-dioksida. Svi uzorci nanokompozita dobijeni su in situ polimerizacijom preko slobodnih radikala metil metakrilata (MMA) u prisustvu čestica punila. Površinska modifikacija korišćenih nanočestica titan-dioksida izvršena je palmitatom askorbinske kiseline. Uzorci nanokompozita su pripremljeni polimerizacijom metil metakrilata u rastvoru, u masi i suspenzionom polimerizacijom. Određene su vrednosti molarne mase PMMA ekstrahovanog iz kompozitnih uzoraka i dobijeno je da su one manje od vrednosti molarne mase čistog PMMA dobijenog na isti način, na osnovu čega se može zaključiti da nanočestice TiO2-PAA prisutne u toku polimerizacije u sva tri slučaja utiču na reakcije terminacije i dovode do smanjenja molarne mase PMMA matrice. Diferencijalnom skenirajućom kalorimetrijom i termogravimetrijskom analizom utvrđeno je i da način sinteze polimerne matrice i koncentracija čestica punila utiču na termička svojstva dobijenih polimernih nanokompozita.

Two series of polyurethane (PU) networks based on Boltorn ® hyperbranched polyester (HBP) and hydrox- yethoxy propyl terminated poly(dimethylsiloxane) (EO-PDMS) or hydroxy propyl terminated poly(dimethylsiloxane) (HP- PDMS), were synthesized. The effect of the type of soft PDMS segment on the properties of PUs was investigated by Fourier transform infrared spectroscopy (FTIR), contact angle measurements, surface free energy determination, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC). The surface characterization of PUs showed existence of slightly amphiphilic character and it revealed that PUs based on HP-PDMS have lower surface free energy, more hydrophobic surface and better waterproof performances than PUs based on EO-PDMS. PUs based on HP- PDMS had higher crosslinking density than PUs based on EO-PDMS. DSC and DMTA results revealed that these newly- synthesized PUs exhibit the glass transition temperatures of the soft and hard segments. DMTA, SEM and AFM results confirmed existence of microphase separated morphology. The results obtained in this work indicate that PU networks based on HBP and PDMS have improved surface and thermomechanical properties.

The characterization of textured yarn is of great significance for both producers and final users. The influence of the texturing parameters (draw ratio and heater temperature) on the characteristics of the textured polyamide yarn has been investigated in this study. Textured yarn was charc- acterized by the degree of orientation, degree of crystallinity, breaking characteristics, shrinkage, elasticity characteristics, the contents of the end groups and degree of whiteness. It was observed that the mentioned characteristics changed as a function of time. The influence of yarn ageing on its characteristics was assessed. The parameters of polyamide textured yarn structure were determined by DSC.

A series of acrylate functionalized samples based on hyperbranched hydroxy-terminated polyesters with different molecular weights and different degrees of acrylation were synthesized. The obtained urethane acrylates were slightly yellow viscose liquids. Their composition was characterized by FTIR and 1H-NMR spectroscopy and their molecular weights were measured by GPC. All the synthesized samples were diluted with 25 wt.% 1,4-butanediol dimethacrylate (BDDM). The rheological properties of the uncured samples and the dynamic mechanical properties of the UV cured samples were examined. All the samples exhibit Newtonian behavior, which indicates the absence of physical entanglements in these polymers. The viscosity increases with increasing number of acrylic groups permolecule. The glass transition temperature of the UV cured samples increases with increasing the number of acrylic groups permolecule. The value of the storage modulus in the rubber-elastic plateau and the cross-link density increase with increasing number of acrylic groups permolecule. The formed networks are inhomogeneous and the residual unsaturation is the highest in the samples with the largest number of acrylic groups per molecule.