Maria Alice Gomes de Andrade Lima

Sucrose hydrolysis catalyzed by auto-immobilized invertase into intact cells of Cladosporium cladosporioides

The enzyme known as invertase ( E.C. 3.2.1.26 - β-D-fructofuranosidase ) catalyzes the sucrose hydrolysis producing an equimolar mixture of glucose and fructose named inverted sugar. The fungus Cladosporium cladosporioides has invertase as its constituent. Hence, its use as a natural immobilized support for the invertase produces interesting results for the enzyme. The present work has the objective of determining the optimum operational conditions of auto-immobilized invertase, as well as its kinetic parameters (K M and V max ). A complete 2 3 factorial planning was done for the evaluation of such parameters. Temperature, pH and agitation level were the studied variables. The hydrolysis percentage was the monitored result. Batch tests in optimum conditions were done to determine the kinetic parameters. Temperature of 70oC, pH 6 and agitation of 170 rpm were the established conditions for the hydrolysis process. The auto-immobilized invertase presented a K M of 447 mM and V max of 2,805 mmol/min.

Evaluation of the types of starch for preparation of LDPE/starch blends

Nesse trabalho foi realizado um estudo sobre diferentes tipos de amido quanto ao crescimento, e a atividade amilolitica de culturas mistas e isoladas dos fungos Phanerochaete chrysosporium e Talaromyces wortmannii. Avaliaram-se tambem as propriedades termicas e mecânicas das blendas de polietileno/amido anfotero (na proporcao 80/20 (m/m)) antes e apos a inoculacao das culturas mistas desses fungos.O amido regular Amidex 3 e o amido modificado Fox5901 foram os que se destacaram quanto ao crescimento celular e producao da enzima amilase. Apesar do pouco tempo de exposicao dos filmes com os fungos, pode-se concluir que os microrganismos promovem mudancas fisicas e quimicas na estrutura da blenda, modificando suas propriedades termicas e mecânicas. A alteracao do grau de cristalinidade e das propriedades mecânicas das blendas podem ser indicios da modificacao provocada pelo processo de biodegradacao.

Corrosion of Galvanized Steel Under Different Soil Moisture Contents

Galvanized steel has been widely applied in different applications and the industry significantly increased its production in recent years. Some galvanized structures can be completely or partially buried, such as transmission tower footings. The corrosion of these metallic structures is related to the soil chemical and physicochemical properties, which define the aggressiveness of the environment. To assess the effect of the soil moisture on galvanized steel corrosion, a comparative study was carried out. Carbon steel coupons, with or without galvanization, were buried in clay soil collected from an industrial region in the northeast of Brazil. The chemical, physicochemical and microbiological characteristics of the soil were determined. The thickness of the galvanized coating was measured by scanning electron microscopy (SEM). Corrosion tests were conducted in different soil moisture conditions using the following techniques: potentiodynamic polarization curves and gravimetric tests. The results showed the influence of soil moisture on corrosion rates. The electroplating decreased corrosion rates, especially when the coupons were exposed to low moisture soil.

Effect of the radiolitic sterilization in polyethylene/starch blends

Samples of LDPE/modified starch blends 80/20 m/m before and after exposure to gamma rays were examined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. The effect of gamma radiation is clearly seen in the samples irradiated at a dose of 25 kGy. The main alteration in the polymeric material after exposure at the radiation range was a decrease in the mechanical properties, alterations in the chemical structure of the blend with an increase in the carbonyl and vinyl indices and the appearance of new crystalline symmetry generating a crystalline domain not existing before in the blend.

Evaluation of photodegradation in LDPE/modified starch blends

Photodegradation of LDPE/modified starch blends 80/20 m/m has been examined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X ray diffraction (DRX) before and after exposure to ultraviolet radiation (UV). Samples were exposed to UV in the laboratory for periods of 6, 24, 48 and 60 hours. The main alteration in the polymeric material after exposure to the radiation was a decrease in the mechanical properties, tensile strength and elongation. There were also changes in the chemical structure of the blend with an increase in the carbonyl and vinyl indices, 65.58 and 53.29%, respectively. The analysis of the blend crystallinity pointed to the formation of a new crystalline symmetry that did not exist before the irradiation.

Control of microbiological corrosion on carbon steel with sodium hypochlorite and biopolymer.

In the present work, the interaction of a mixture of a biocide, sodium hypochlorite (NaClO), and a biopolymer, xanthan, with carbon steel coupons exposed to seawater in a turbulent flow regime was studied. The cell concentrations, corrosion rates, biomasses, and exopolysaccharides (EPSs) produced on the coupon surfaces with the various treatments were quantified. The corrosion products were evaluated using X-ray diffraction (XRD), and the surfaces of steels were analysed by scanning electron microscopy (SEM). The results indicated that xanthan and the hypochlorite-xanthan mixture reduced the corrosion rate of steel.

Influence of Composite Nano-Coating of Ni-Co-SiC Obtained by Electrodeposition on the Corrosion Resistance of API 5L X80 Steel

Corrosion problems are frequent and occur in various sectors of industries, resulting consequences of economic order and serious accidents involving human lives and contaminating the environment. The electrodeposition is one of the most popular methods for preventing corrosion, where the Ni-Co metal matrix has been widely applied. The incorporation of SiC nano-particles in electrochemical baths produces nanocomposite coatings to synergistic properties with potential application in anti-corrosion protection. The objective of this work was to develop the Ni-Co-SiC nano-coating electrodeposited on API 5L X80 steel and evaluate the corrosion resistance. Open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PP) measurements were performed in 3.5% NaCl solution. To correlate with corrosion behavior, scanning electron microscopy (SEM), energy-dispersive X-ray spectrum (EDXS) and Vickers micro-hardness tests on the nano-coating were performed.

Corrosion by Sulfate Reducing Bacteria in Welded Joints of Stell API 5L X80

Articles report that the sulphate reducing bacteria (SRB) are the main micro-organisms related to cases of corrosion. They reduce the sulfate ion resulting in the production of sulfide, disulfide and hydrogen sulfide, potential agents of corrosion of ferrous materials. This study investigated the action of sulfate-reducing bacteria on corrosion test specimens with welded joint of API 5L X80 steel in the presence of seawater. The samples were exposed to sea and sterilized water was then added to BRS. Microorganisms were quantified periodically calculated the corrosion rate and weight loss, and the surfaces of the samples analyzed by light microscopy.

The influence of centrifugation on Zymomonas mobilis aggregation

Flocculent Zymomonas mobilis breaks down in smaller flocs and individual cells when centrifuged. The main consequence of it is an increase in the dispersion of the sample, suggesting that the influence of the centrifugal force on the aggregation of cells is worth to study. The experiments showed that the degree of dispersion varied between 30% and 100% when the centrifugal acceleration changed from 25 g to 2500 g. Observation under the electronic microscope showed that a slimy material covered the cells recovered by gentle gravitational settling and, that the centrifuged cells presented a bare cell wall.