Synthesis and characterization of microcrystalline cellulose produced from bacterial cellulose

In this study, microcrystalline cellulose (MCC) was prepared from the acid hydrolysis of bacterial cellulose (BC) produced in culture medium of static Acetobacter xylinum. The MCC-BC produced an average particle size between 70 and 90 mu m and a degree of polymerization (DP) of 250. The characterization of samples was performed by thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy (SEM). The MCC shows a lower thermal stability than the pristine cellulose, which was expected due to the decrease in the DP during the hydrolysis process. In addition, from X-ray diffractograms, we observed a change in the crystalline structure. The images of SEM for the BC and MCC show clear differences with modifications of BC fiber structure and production of particles with characteristics similar to commercial MCC.

Binuclear cyclopalladated compounds with antitubercular activity: synthesis and characterization of [{Pd(C-2,N-dmba)(X)}(2)(mu-bpp)] (X = Cl, Br, NCO, N-3; bpp=1,3-bis(4-pyridyl)propane)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Spectroscopic studies on glassy Ni(II) and Co(II) polyphosphate coacervates

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Synthesis and characterization of silver nanoparticles impregnated into bacterial cellulose

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Thermal decomposition of solid state compounds of lanthanide and yttrium benzoates in CO2 atmosphere

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The Effect of the Aminic Substituent on the Thermal Decomposition of Cyclic Dithiocarbamates

Estudos termogravimétricos e calorimétricos diferenciais para ditiocarbamatos de NH4+, Na+, Zn2+, Cd2+ e Pb2+, derivados de aminas cíclicas contendo nitrogênio como heteroátomos, foram realizados em atmosferas de ar e nitrogênio, para avaliar a influência da tensão angular dos anéis na decomposição térmica destes compostos, em relação à formação de tiocianatos metálicos como via de decomposição. Os intemediários formados foram caracterizados por difração de raios-X, tendo sido encontrados oxissulfatos de Zn2+, Cd2+ e Pb2+, sob atmosfera de ar, o que sugere a decomposição térmica nestas condições como via sintética para estes compostos. Os produtos de decomposição final obtidos foram sulfetos metálicos sob nitrogênio e óxidos dos metais de transição e sulfato de sódio sob ar. Entalpias de fusão são também descritas, com base nos resultados de DSC.

Caracterização mecânica e térmica de compósitos de poli (cloreto de vinila) reforçados com fibras de sisal

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Thermal and mechanical properties of PVDF/PANI blends

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

SYNTHESIS OF ULTRA-FINE CRYSTALLINE ZRXTI1-XO4 POWDER BY POLYMERIC PRECURSOR METHOD

Reactive ZrxTi1-xO4 (x=0.65, 0.50 and 0.35) powder was prepared by the polymeric precursor method. Studies by X-ray diffraction (XRD), nitrogen adsorption/desorption, and thermogravimetric analysis (TG) showed that powders with high crystallinity (>90%) and high surface areas (>40 m(2)/g) are obtained after calcination at 700 degrees C for 3 h. Infrared spectroscopy and XRD results showed that these titanates nucleate from the amorphous phase with no intermediate phases, at low temperature (450 degrees C).

Non-isothermal kinetic applied to thermal decomposition of commercial alkyd varnish

Samples of commercial alkyd resin varnish were spread in a film form on slides, dried at room temperature and exposed to solar radiation from one day up to seven months.Thermogravimetric measurements have been done. Based on the TG data, the Flynn-Wall isoconversional method was applied. The activation energy varied between 176-154 kJ mol(-1) and logA was between 15.5-12.9 min(-1) for A, B and C samples at 95% confidence level.

Sintering of ultrafine undoped SnO2 powder

The sintering process of nanometric undoped SnO2 powder was studied. No macroscopic shrinkage was observed during the sintening process. Grain growth kinetics investigation showed that surface diffusion is the dominant mechanism in the temperature range 500-1300 degreesC. For temperatures higher than 1300 degreesC, high weight loss was measured, suggesting evaporation-condensation as the dominant mass-transport mechanism. Thermogravimetric analysis (TG) and mass spectroscopy studies showed that the surface contamination of the SnO2 particles by chemical species like H2O, OH- and CO2, has a strong influence on the role of mass transport controlled by surface diffusion. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Synthesis and characterization of Li2ZnTi3O8 spinel using the modified polymeric precursor method

In this work we report the synthesis procedure, crystallographic, structural and magnetic properties of the Li2ZnTi3O8 spinel obtained using a modified polymeric precursor method. This synthesis method generates very reactive and property-controlled nanoparticles. The samples were characterized using X-ray powder diffraction (XRD) associated to the Rietveld refinement method, thermogravimetric analysis (TG), specific surface area, scanning electron microscopy (SEM) and magnetic susceptibility measurements.The phase formation temperature of the lithium zinc titanate spinel was observed to decrease due to the homogeneity and highly controlled nanometric particle size. (C) 2003 Elsevier B.V. All rights reserved.

Effect of the temperature on the TMOS sono-hydrolysis and a study of the structure of the resulting aged sonogels

The effect of temperature on the oxalic acid catalyzed sono-hydrolysis of tetramethoxysilane (TMOS) was studied by means of a heat flux calorimetric method. The activation energy of the process was measured as (24.5 +/- 0.8) kJ/mol in the temperature range between 10 and 50 degreesC. The structural characteristics of the resulting sonogels, after long period of aging in saturated conditions, were studied by means of small angle X-ray scattering. The structure can be described as formed by similar to2.7 nm mean size mass fractal-like aggregates (clusters) of primary silica particles of similar to0.3 nm mean size, all imbibed in a liquid phase. The average mass fractal dimension of the clusters was found to be 2.58. The primary particle density was estimated as 2.23 g/cm(3), in good agreement with the value frequently quoted for fused silica. The volume fraction of the clusters, in the saturated sonogels was estimated as about 28%. The moment in which the meniscus of the liquid phase penetrates into the clusters under rapid evaporation process has been detected by an inflection in the first derivative of the curve of weight loss in a simple thermogravimetric test. (C) 2003 Elsevier B.V. All rights reserved.

An investigation of the thermal behavior of heterobimetallic species containing copper(II) and tetracyanopalladate(II)

Synthesis, characterization and thermal behavior of four compounds that have the general formula [Cu{Pd(CN)(4)}(L)(x)](n), in which en = 1,2-diaminoethane and pn = 1,3-diaminopropane (L = en, x = 1 (I); L = pn, x = 1 (II); L = en, x = 2 (III); L = pn, x = 2 (IV)) were described in this work. The complexes were studied by elemental analysis, infrared spectroscopy (IR), differential thermal analysis (DTA) and thermogravimetry (TG) and the residues of the thermal decomposition were characterized by X-ray powder diffraction and found as a mixture of CuO and PdO. The stoichiometry of the compounds was established via thermogravimetric and elemental analyses and their structures were proposed as coordination polymers based on their infrared spectra. The following thermal stability sequence was found: IV < I=II < III.

Functionalized silica synthesized by sol-gel process

This work considers some aspects of the chemistry involved in the preparation and description of silicon oxide functionalized by sol-gel process. In this work we studied the synthesis and measured the properties of silicon oxide functionalized with 3-chloropropyl, through a sol-gel process. Thermogravimetic analysis, infrared spectra, and elemental analyses were measured. The samples were prepared in the following proportions of tetraethylorthosilicate (TEOS): 3-chloropropyl trimethoxisilane molar ratio: 1:0, 1:1, 2:1, 3:1 and 4:1. The thermogravimetric data for the resulting materials established the 'minimum formulae' 2:0, 3:1, 4.1, 7:1 and 11:1, respectively. As expected, the relative amount of water is inversely proportional to the presence of propyl groups. Infrared data show Si-C and -CH2-vibration modes at 1250 to 1280 and 2920 to 2940 cm(-1), respectively. Thermogravimetric data and infrared spectra showed that inorganic polymers contained organic polymers. (C) 1999 Elsevier B.V. B.V. All rights reserved.