Navegando por Palavras-chave "nanocomposites"
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- ItemAcesso aberto (Open Access)Biopolymer-clay nanocomposites: cassava starch and synthetic clay cast films(Sociedade Brasileira de Química, 2014-02-01) Perotti, Gustavo Frigi; Tronto, Jairo; Bizeto, Marcos Augusto [UNIFESP]; Izumi, Celly Mieko Shinohara; Temperini, Marcia Laudelina Arruda; Lugão, Ademar Benévolo; Parra, Duclerc Fernandes; Constantino, Vera Regina Leopoldo; Universidade de São Paulo (USP); Universidade Federal de Viçosa Instituto de Ciências Exatas e Tecnológicas; Universidade Federal de São Paulo (UNIFESP); Universidade Federal de Juiz de Fora Departamento de Química Núcleo de Espectroscopia e Estrutura Molecular; Instituto de Pesquisas Energéticas e Nucleares Centro de Química e Meio AmbientePolymer-clay nanocomposites (PCN) based on cassava starch, synthetic hectorite clay and inverted sugar cane syrup (plasticizer) were prepared by solvent-assisted (casting) process producing transparent and homogeneous films. Small amounts of clay (5-15 wt.%) resulted mainly in exfoliated nanocomposites while large amounts (30 wt.%) promote the intercalated nanocomposites formation. FT-Raman bands sensitive to hydrogen bonding in starch granules are progressively shifted to lower wavenumbers as the clay content is raised. Nanocomposites show a similar thermal behavior up to 320 ºC while the biomolecule decomposition at about 500 ºC is dependent on the clay content. CO2 release at about 300 ºC (non-oxidative decomposition of polymeric chains) decreases if compared to the gas delivery at ca. 500 ºC, as the clay content is increased. Films with clay content higher than 10 wt.% show no substantial benefit for either elongation or resistance properties.
- ItemAcesso aberto (Open Access)Desenvolvimento de nanocompósitos de poli(3-hidroxibutirato-co-3-hidroxivalerato) com nanopartículas de prata(Universidade Federal de São Paulo (UNIFESP), 2016-02-25) Costa, Flavio de Souza [UNIFESP]; Passador, Fabio Roberto [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)The utilization of biodegradable polymers from natural sources has been attracting attention from the academy and industry due to environmental issues. Among biodegradable polymers, PHBV (poly(3-hydroxybutyrate-co-3-hydroxyvalerate)), a polyhydroxyalkanoate (PHA), is an example of a polymer of renewable origin that presents good biodegradability and processability. In this work PHBV films were developed with the addition of silver nanoparticles (AgNP), synthesized by the Turkevich method of reduction of Ag+ ions of silver nitrate by the oxidation of citrate ions and particle size were controlled by the addition of ammonium hydroxide. During the study the AgNP synthesis temperature were varied (90 °C and 97 °C) and so did the time of addition of ammonium hydroxide (6 minutes and 9 minutes for the synthesis at 90 °C and 3 minutes for the synthesis at 97 °C), in order to obtain the AgNP. Ammonium hydroxide was added to the colloidal suspension to guarantee stability and the nanometric size of the AgNP. The characterization of colloidal nanometric silver suspensions was evaluated by particle size analysis by dynamic light scattering (DLS), measures of zeta potential of the nanoparticles surface, UV-VIS spectroscopy of the colloidal suspensions and also wide angle X-ray diffraction (WAXD) and scanning electronic microscopy (SEM) of the dried powders. The films of neat PHBV and PHBV / AgNP nanocomposites containing 0.1, 0.5, 1.0, 1.5 and 2.0 wt % of AgNP were produced by solution mixing followed by solvent evaporation. The characterization of the films was evaluated by SEM, thermogravimetry (TGA) and differential scanning calorimetry (DSC). Biodegradable essays were carried out in liquid medium to verify the effect of addition of AgNP in the biodegradation process of neat PHBV films and PHBV / AgNP nanocomposites. It wasn´t observed difference in size between the AgNP synthesized at 90 °C with the addition of ammonium hydroxide having happened at 6 minutes or at 9 minutes. The synthesis at 97 °C led to the production of instable AgNP and was discarded as a possible route to synthesize the AgNP. The addition of AgNP to the PHBV matrix increases the crystallinity degree and decreases the thermic degradation temperature of the polymer. The biodegradable essay revealed that the addition of 0.5 wt% of AgNP inhibited the bacteria growth, which avoided the biodegradation of the PHBV matrix.
- ItemSomente MetadadadosInfluence of photodegradation with UV radiation in biotreatment with Paecilomyces variotti on PHBV/GNS nanocomposites(Inst Engineering Technology-Iet, 2018) Montagna, Larissa Stieven [UNIFESP]; Montanheiro, Thais Larissa do Amaral [UNIFESP]; Borges, Aline Chiodi; Koga-Ito, Cristiane Yumi; Lemes, Ana Paula [UNIFESP]; Rezende, Mirabel Cerqueira [UNIFESP]Graphite nanosheets (GNSs) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) nanocomposites were prepared by solution casting method. This study aimed to evaluate the effects of previously phototreatment with ultraviolet (UV) radiation on the biotreatment with Paecilomyces variotti of neat PHBV and PHBV/GNS nanocomposites. Some samples of PHBV film were submitted only to biotreatment with P. variotti during 120 days
- ItemAcesso aberto (Open Access)Nanocompósitos formados por nanotubos de carbono verticalmente alinhados e polidimetilsiloxano (desenvolvimento e caracterização elétrica)(Universidade Federal de São Paulo (UNIFESP), 2015-09-03) Gonzatto Neto, Alfredo [UNIFESP]; Corat, Evaldo Jose [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)Nanocomposites formed by polydimethylsiloxane and carbon nanotubes were produced. Some relationships have been established between mechanical deformation and piezoresistive and capacitive effects through experiments involving deformation analysis and electrical characterizations. This study also allowed us to understand the probable piezoresistividade mechanisms responsible for the electrical characteristics of polymer nanocomposites of carbon nanotubes. Films of vertically aligned multi-walled carbon nanotubes were produced by microwave plasma on Ti substrate / TiN and subsequently integrated and transferred into a polymer matrix made in films form. Electrical DC analysis and AC impedance spectroscopy revealed two distinct contributions: from the physical contact of the carbon nanotubes, and from the no contact between the carbon nanotubes separated by small silicone fills. The second one, gives capacitive effects and especially the tunneling effect. Tunneling effect dependencies were found in relation to the density of the carbon nanotube film, to the applied voltage and range of deflection to which the membrane was subjected, thus influencing the response sensitivity. The nanocomposite behaved regularly under large deformations (910 μԐ to μԐ 90900), presenting Gauge factor between 8.6 and 0.8 in the respective order. In small deformations (10.4 μԐ to 41.6 μԐ) demonstrated good sensitivity, presenting Gauge Factor of 689, attributed to the use of the film in the relaxed state, benefiting from tunneling effect. The results were relevant and of considerable contribution to the study and development of new elastic and flexible sensors.
- ItemAcesso aberto (Open Access)Physical-chemical properties of nanocomposites based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and titanium dioxide nanoparticles(Iop Publishing Ltd, 2018) Braga, Natalia F. [UNIFESP]; da Silva, Ana Paula [UNIFESP]; Arantes, Tatiane Moraes; Lemes, Ana Paula [UNIFESP]; Cristovan, Fernando Henrique [UNIFESP]Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was reinforced with titanium dioxide (TiO2) in concentrations of 1.0%, 2.5% and 5.0% (m/m) to produce nanocomposites by the solvent casting technique. TiO2 was synthesized by a hydrothermal treatment to produce nanoparticles. The nanostructure of the nanoparticles was studied by x-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The XRD confirmed TiO2 crystalline nanoparticles, with a mixture of anatase and rutile phases. Through TEM analysis, the formation of TiO2 nanorod agglomerates with an average diameter and length of 40 and 12 nm, respectively, was observed. The thermal and mechanical properties of the pure PHBV and nanocomposite films were characterized by differential scanning calorimetry (DSC) and dynamic mechanical analysis. The DSC analysis showed that the glass transition temperature decreased with the inclusion of TiO2 in the PHBV matrix in relation to pure PHBV. The results of biodegradation assays for the PHBV and nanocomposites in an aqueous medium and in soil showed morphological and structural changes for all samples, indicating a high biodegradation rate for this material. The most important conclusion is that the biodegradation of the PHBV was not affected by the addition of nanoparticles, thus enabling the use of nanocomposites in applications requiring biodegradable materials.
- ItemAcesso aberto (Open Access)Polymer Nanocomposites for Hydrogen Storage(Amer Inst Physics, 2017) Beatrice, Cesar A. G.; Oliveira, Amanda D.; Passador, Fabio R. [UNIFESP]; Pessan, Luiz A.Hydrogen is considered to be a clean, economical and safe renewable energy source that would be ideal to replace fossil fuels, because it is light, highly abundant and its oxidation product (water) is environmentally benign. However, hydrogen is easy to burn (the chemical energy per mass of hydrogen is at least three times larger than that of other chemical fuels), which has the risk of fire and explosion. The problems of transportation and storage restrict the application of hydrogen energy, which has become a key factor in the development and utilization of hydrogen energy. This gas adsorbs at solid surfaces depending on the applied pressure and temperature. For storage purposes in mobile applications, the adsorption of hydrogen has been studied mainly on carbon species, but light and reasonably cheap materials of high surface area should prove to be attractive as well. Porous material is a very promising hydrogen storage material, which stores the gas in the form of molecules at low temperatures and compresses hydrogen into the holes effectively. The purpose of this work was to develop a hybrid porous materials consisting of sulfonated polyetherimide matrix with aluminum nanoparticles and faujasite type zeolite. Dilute solutions were first prepared under stirring at room temperature and the solutions were dried under vacuum. The hybrids were analyzed by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and hydrogen sorption measurements. The addition of aluminum decreased the glass transition temperature of the hybrids when compared to the sulfonated polymer and the TEM images showed that simply physically mixture occurred between polymer and metallic nanoparticles. Hydrogen sorption tests showed an increase in the amount of hydrogen in the presence of zeolite.
- ItemAcesso aberto (Open Access)Preparação e caracterização de nanocompósitos estruturais baseados em poli(3-hidroxibutirato-co-hidroxivalerato) e nanopartículas de dióxido de titânio para o emprego em engenharia tecidual(Universidade Federal de São Paulo (UNIFESP), 2015-10-30) Braga, Natalia Ferreira [UNIFESP]; Cristovan, Fernando Henrique [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)Preparation and characterization of structural nanocomposites based on poly (3-hydroxybutyrate-co-hydroxyvalerate) and titanium dioxide nanoparticles for use in tissue engineering In this work it was developed nanocomposites based on poly (3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) and titanium dioxide (TiO2), by means of three different techniques: casting, electrospinning, and spin-coating. Therefore, the TiO2 nanoparticles were synthesized by hydrothermal treatment of PCT gel (titanium peroxo complex). The nanoparticles had a rod format with average diameter of 12 nm and an average length of 40 nm with predominantly of rutile crystallographic phase. Subsequently, PHBV nanocomposites were prepared with different proportions of TiO2 nanoparticles (1%, 2.5% and 5% w/w) and compared with the neat polymer as its physical-chemical and thermal properties. In general, the nanoparticles catalyzed the process of biodegradation and photo-degradation of the PHBV polymer matrix. DSC analysis showed that the Tg of the material decreases with the inclusion of TiO2 and by TGA revealed that the degradation temperature is smaller in nanocomposites compared to pure polymer. While, DMA analysis indicated that there was an increase in the damping properties of the nanocomposites compared to PHBV. Finally, mats were prepared by electrospinning to verify cell viability of the nanocomposites. SEM analyzes showed the formation of interconnected continuous fibers, so candidates for use in tissue engineering. Thus, the study of cell viability was conducted in the nanocomposites, which showed that the cells growth on PHBV mats showed good cell adhesion and proliferation rate and, in general, treatment with TiO2 increased cell growth. Membranes prepared by spin-coating technique showed very thin thickness that ranged from 3.8 ?m to 9.1 ?m.