ABSTRACT: Polymer coatings are used to control the rate of release of plant available nutrients from fertilizers as well as to reduce nutrient losses such as ammonia (NH3) volatilization. Although the literature presents several examples of materials used to coat urea, little is known about nitrogen (N) release properties such as the mechanism involved and phenomena (e.g., pore opening) in the polymer coating. Thus, this study investigated urea release from polyurethane (PU) derived from two renewable raw materials (castor oil and soybean oil), to explain how the oil structure and coating microstructure influence release and urea-N dynamics in soil. The results demonstrated that the profile of urea release and the urea-N mineralization in the soil could be controlled by altering the thickness of the coating on the urea granules. Coating by eco-friendly polymer was efficient in controlling urea release in soil to reduce volatilization of ammonia and increase the availability of N in the soil.

Um eletrodo de pasta de carbono modificado com dióxido de chumbo imobilizado em uma resina de poliéster foi desenvolvido para a determinação voltamétrica de pulso diferencial simultânea de L-dopa e carbidopa em formulações farmacêuticas. As curvas analíticas foram lineares em uma faixa de concentração de 2,6 <FONT FACE=Symbol>´</FONT> 10-4 a 1,2 <FONT FACE=Symbol>´</FONT> 10-3 mol L-1 e de 3,2 <FONT FACE=Symbol>´</FONT> 10-5 a 1,5 <FONT FACE=Symbol>´</FONT> 10-4 mol L-1 para L-dopa e carbidopa, respectivamente. Os limites de detecção foram 2,5 <FONT FACE=Symbol>´</FONT> 10-5 mol L-1 e 3,7 <FONT FACE=Symbol>´</FONT> 10-6 mol L-1 para L-dopa e carbidopa, respectivamente e as recuperações de L-dopa e carbidopa em duas amostras variaram de 98,1 a 103%. Os desvios padrão relativos foram menores que 2,5% para soluções 1,2 <FONT FACE=Symbol>´</FONT> 10-4 e 1,2 <FONT FACE=Symbol>´</FONT> 10-3 mol L-1 dessas catecolaminas e os resultados obtidos para L-dopa e carbidopa em formulações farmacêuticas usando o procedimento voltamétrico proposto estão em boa concordância com os valores rotulados ou com aqueles teores determinados empregando-se um procedimento enzimático a um nível de confiança de 95%.

A carbon paste electrode modified with lead dioxide immobilized in a polyester resin has been developed for simultaneous differential pulse voltammetric determination of L-dopa and carbidopa in pharmaceutical formulations. The analytical curves were linear in the concentration ranges from 2.6 <FONT FACE=Symbol>´</FONT> 10-4 to 1.2 <FONT FACE=Symbol>´</FONT> 10-3 mol L-1 and from 3.2 <FONT FACE=Symbol>´</FONT> 10-5 to 1.5 <FONT FACE=Symbol>´</FONT> 10-4 mol L-1 for L-dopa and carbidopa, respectively. The detection limits were 2.5 <FONT FACE=Symbol>´</FONT> 10-5 mol L-1 and 3.7 <FONT FACE=Symbol>´</FONT> 10-6 mol L-1 for L-dopa and carbidopa, respectively and recoveries of L-dopa and carbidopa from two samples ranged from 98.1 to 103% of the added amount. The relative standard deviations were lower than 2.5% for 1.2 <FONT FACE=Symbol>´</FONT> 10-4 and 1.2 <FONT FACE=Symbol>´</FONT> 10-3 mol L-1 of these catecholamines solutions and the results obtained for L-dopa and carbidopa in pharmaceutical formulations using the proposed voltammetric procedure are in close agreement with the labeled values and/or those obtained using an enzymatic method at the 95% confidence level.

The use of fluidized bed combustors to burn coal is largely studied to permit the addition of limestone to capture SO2. The particle size for coal and limestone is an important parameter in this process. Thermogravimetry (TG) is used to elucidate the combustion and sulfation processes, but the experimental parameters must be evaluated to be representative in fluidized bed combustors. In the present study the effect of particle size is analyzed in the calcination of limestones and the combustion of coal through the thermogravimetric curve for limestone and derivative thermogravimetric curve for coal. Small peaks representing mass losses between 400 and 500 ºC are observed due to the jumping of particles out of the crucible. This effect, recognized as decrepitation is observed for mid-sized particles provoked by the release of water vapor trapped within their lattice.

The SEC and VPO behaviour of hydroxyl-terminated polybutadiene resins was investigated using toluene as solvent and polybutadiene and polystyrene as standards. The results show that molar mass obtained depend on the nature of the standards used in the calibration, specialy in SEC analysis.