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De Britto D.,EMBRAPA - Empresa Brasileira de Pesquisa Agropecuaria | Assis O.B.G.,Embrapa Instrumentacao Agropecuaria
Packaging Technology and Science | Year: 2010

Aiming to improve the homogeneity of films based on chitosan to be applied as edible coating, we carried out some chemical modifications in the polymeric structure by reductive alkylation and quaternization reactions. The resulting derivatives had different hydrophilic behaviours and cast films were characterized by wetting, swelling and topographic measurements. Concerning wetting, all samples presented similar time dependence with receding water contact angles. The quaternized chitosans were the most hydrophilic derivatives, with lower values of contact angles when compared with the parent sample. These derivatives also exhibited a higher swelling tendency. The analysis shows that the relative amount of absorbed water increases according to the length of moiety added. In general, the cast films of chitosan showed good homogeneity, displaying low roughness and regular distribution over a polar surface. On the other hand, alkyl quaternary salts showed an irregular topography with undulation and mountain-like formation due probably to agglomeration of polymeric chains. The final film morphology was dependent on the polymer solubility, as observed by microscopic techniques. Copyright © 2010 John Wiley & Sons, Ltd. Source

De Andrade F.D.,University of Sao Paulo | Netto A.M.,University of Sao Paulo | Colnago L.A.,Embrapa Instrumentacao Agropecuaria
Talanta | Year: 2011

The Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence has been used in many applications of magnetic resonance imaging (MRI) and low-resolution NMR (LRNMR) spectroscopy. Recently, CPMG was used in online LRNMR measurements that use long RF pulse trains, causing an increase in probe temperature and, therefore, tuning and matching maladjustments. To minimize this problem, the use of a low-power CPMG sequence based on low refocusing pulse flip angles (LRFA) was studied experimentally and theoretically. This approach has been used in several MRI protocols to reduce incident RF power and meet the specific absorption rate. The results for CPMG with LRFA of 3π/4 (CPMG135), π/2 (CPMG90) and π/4 (CPMG45) were compared with conventional CPMG with refocusing π pulses. For a homogeneous field, with linewidth equal to Δυ = 15 Hz, the refocusing flip angles can be as low as π/4 to obtain the transverse relaxation time (T2) value with errors below 5%. For a less homogeneous magnetic field, Δυ = 100 Hz, the choice of the LRFA has to take into account the reduction in the intensity of the CPMG signal and the increase in the time constant of the CPMG decay that also becomes dependent on longitudinal relaxation time (T 1). We have compared the T2 values measured by conventional CPMG and CPMG90 for 30 oilseed species, and a good correlation coefficient, r = 0.98, was obtained. Therefore, for oilseeds, the T2 measurements performed with π/2 refocusing pulses (CPMG 90), with the same pulse width of conventional CPMG, use only 25% of the RF power. This reduces the heating problem in the probe and reduces the power deposition in the samples. © 2011 Elsevier B.V. All rights reserved. Source

Regitano J.B.,University of Sao Paulo | Rocha W.S.D.,Embrapa Gado de Leite | Bonfleur E.J.,Federal University of Parana | Milori D.,Embrapa Instrumentacao Agropecuaria | Alleoni L.R.F.,University of Sao Paulo
Journal of Agricultural and Food Chemistry | Year: 2016

We evaluated the effects of soil water content on the retention of diuron and its residual distribution into organomineral aggregates in four Brazilian oxisols. 14C-Diuron was incubated for days at 25, 50, and 75% of maximum water-holding capacity for each soil. After 42 days, the physical fractionation method was used to obtain >150, 53-150, 20-53, 2-20, and <2 μm aggregate sizes. Diuron retention increased with increasing soil water content for all soils. At lower soil water content, diuron's retention was higher in the sandier soil. It was mostly retained in the fine (<20 μm) aggregates of sandier soil, and for clayed soils, retention was higher in the coarse aggregates (>53 μm). The sorption coefficients (Kd and Koc) generated by batch studies should be carefully used because they do not provide information about aggregation and diffusion effects on pesticides soil sorption. © 2015 American Chemical Society. Source

Alteration in hydrophilicity feature of chitosan films by hexamethyldisilazane (HMDS) cold-plasma treatment is evaluated. All treated films were colorless and transparent with no apparent textural changes. The effect on surfaces was characterized through contact angle measurements, degree of swelling and water vapor permeation. A significant reduction in all of the hydrophilicity parameters was observed. It is assumed that the HMDS treatment forms nonpolar silicone type structures. The goal is to investigate the formation of a stable hydrophobic barrier in order to increase the chitosan films usefulness in packaging applications. Source

Giraldi T.R.,Institute Ciencia e Tecnologia UNIFAL | Santos G.V.F.,DQF CCEN UFPE | Mendonca V.R.,Federal University of Santa Catarina | Ribeiro C.,Embrapa Instrumentacao Agropecuaria | Weber I.T.,DQF CCEN UFPE
Journal of Nanoscience and Nanotechnology | Year: 2011

This paper describes the development of ZnO nanoparticles by a chemical method, to test them in the photocatalysis of the degradation of textile dyes, using Rhodamine B (RhB) as a probe reaction. The samples were submitted to different heat treatments in order to observe the annealing effects on the photocatalytical properties, surface decontamination and the consequent particle change, in terms of crystallinity. The as-prepared samples (ZOA) correspond to a metastable phase (oxy or hydroxy zinc acetate) and post annealing leads to ZnO crystallization. In spite of the XRD patterns showing only the ZnO phase for heat treatment at 100 °C, FTIR data show that carboxylate groups remains attached to the ZnO surface up to 300 °C. Up to 300 °C the presence of these carboxylate groups, provided by the synthesis method, showed to be more relevant to photoactivity than the specific surface area. At higher temperatures, crystallinity becomes the dominant factor and an increasing of crystallinity favors the photoactivity. Copyright © 2011 American Scientific Publishers. Source

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