The influence of cashew nutshell liquid (CNSL) in the oxidative stability of biodiesels prepared from oils of soy, corn, canola and sunflower was studied using the Rancimat method. The induction periods at 110 ºC, without and with the addition of CNSL at concentrations of 0.1, 0.5 and 1.0% m/m, were determined and clearly show an important increase in the oxidative stability proportional to the concentration of the additive. For example, with the addition of 0.1% m/m CNSL, the induction period, in hours, increased from 5.7 to 8.5 (soy biodiesel), from 1.7 to 4.0 (sunflower), from 4.3 to 9.3 (corn) and from 6.9 to 12.8 (canola). The rate constants of the oxidation reactions in presence of CNSL were also determined and their respective values are (in h -1 ): 0.77 ± 0.08, 2.48 ± 0.46, 0.94 ± 0.08, 0.51 ± 0.11. The activation parameters (enthalpy, ∆H*, entropy, ∆S*, and free energy of activation, ∆G*) for the oxidation reactions were determined.

Os materiais fixados em polímeros são cada vez mais utilizados como ferramentas didáticas, devido a sua resistência, praticidade, facilidade de manuseio e aproximação com o objeto real de estudo, permitindo a compreensão dos aspectos morfológicos externos dos espécimes. Diante disso, verificamos a efetividade do método, através da técnica de incrustação de insetos, no processo de ensino-aprendizagem de discentes do terceiro ano do Ensino Médio. Inicialmente, aplicou-se um questionário, avaliando o conhecimento prévio dos alunos sobre a morfologia externa de exemplares de insetos. Em seguida, ministrou-se uma aula com os materiais incrustados, permitindo a manipulação e a visualização dos exemplares. Por fim, os discentes responderam ao questionário inicial novamente, verificando e validando o processo. Os dados obtidos indicam que as incrustações de insetos contribuíram para a compreensão das estruturas morfológicas externas. Portanto, se utilizada pelos docentes como ferramenta didática pode atuar efetivamente no processo de ensino-aprendizagem dos discentes.

No abstract

A simple and selective spectrophotometric method has been developed for the first time for the determination of sodium methoxide in methanol solution in the presence of sodium hydroxide. The developed method involves the formation of a pink species by the reaction between sodium methoxide and α-santonin. The pink compound formed shows absorbance maximum at 513 nm. N, N-Dimethylformamide and methanol were used as solvents, and the reaction was performed at different temperatures and 25 °C was selected for further experiments. The pink compound formed was dried and then was studied using FTIR and mass spectrometry. The calibration curve was constructed from 0.10 to 0.30% (m/v) sodium methoxide in methanol, and the standard deviation is 0.010%. Similarly, the relative standard deviations of 28%, 26%, and 24% solutions of sodium methoxide were obtained in the range of 0.4 to 1.9%. The correlation coefficient of the analytical curve r = 0.9997; the limit of detection, LOD, is ca. 1.1 × 10 % w/w; and the limit of quantification, LOQ, is ca. 3.2 × 10 % w/w. The results of analysis were validated statistically.

No abstract