Gelatin-based films containing soy lecithin or Yucca schidigera extract and glycerol as plasticizer were produced by casting and characterized for their mechanical properties, water vapor permeability (WVP), water solubility, opacity and morphology. The addition of glycerol reduced the tensile strength, with a difference of ~ 68% between the values for the minimum and maximum concentrations evaluated, both for the plasticizer and the surfactant. Elongation values reached 52% and 40%, for films containing yucca extract and lecithin, respectively, when higher amounts of plasticizer and surfactant were added. Lower values of WVP were obtained when the intermediate concentration of glycerol (20 g plasticizer/100 g protein) was used, reaching 0.14 and 0.15 g mm/m² h kPa, respectively, for films containing yucca extract and lecithin. The solubility was not affected by adding plasticizer and / or surfactants. The morphologies of the inner sections of the films, regardless of type of surfactant used, were compact, without pores or phase separation, indicating efficient incorporation of the compounds added to the protein matrix.

The objective ofthis work was to study the thermal and visco-elastic properties of films based in blends of gelatin and PVA, using dynamic-mechanical analysis. The results of the DMA had shown thatthe films with 10% of PVA presented only one peak in tanδ. With the increase of the PVA concentration, however, appear two relaxations in the curve of tanδ, that is, two Tg. On the other hand, in the tests of scanning frequency in DMA, the values of the storage module had diminished with the increment of the temperature. The WLF model was applied, determining the values of its constants, that had increased with the increase of the concentration of PVA in the blend: C1=49-66 and C2=463-480 K.

El objetivo del presente trabajo fue estudiar las propiedades térmicas y viscoelásticas de films elaborados a base de mezclas de gelatina y PVA, utilizando análisis dinámico-mecánico. Los resultados de DMA mostraron que los films con 10% de PVA presentaban solamente un pico en el espectro de tanδ. Con el aumento de la concentración de PVA los espectros mostraron dos relajaciones en la curva de tanδ, esto es, dos Tg. Por otro lado, en las pruebas de barrido de frecuencia en DMA, los valores del módulo de almacenamiento disminuyeron con el incremento de temperatura en los espectros obtenidos. El modelo de WLF fue aplicado, determinándose los valores de sus constantes, que aumentaron con el incremento de PVA en la mezcla: C1=49-66 e C2=463-480 K. Partiendo de estos valores fueron calculados el volumen libre fraccionario del sistema en la Tg y el coeficiente de expansión térmica.

Edible films are thin materials based on biopolymers and food additives. The aim of this work is a review on the application of dynamic mechanical analysis in edible film technology. After a brief review of the linear visco-elasticity theory, a description of some practical aspects related to dynamic mechanical analysis, such as sample fixation and sample dehydration during analysis and types and modes of tests are presented. Thus, the use of temperature scanning analysis for glass transition and for plasticizer-biopolymer compatibility studies and frequency scanning tests, less common in edible film technology, are critically reviewed.

Resumo: As poucas mudanças no modelo de transmissão/recepção, usado por muitos professores em suas salas de aula, levaram-nos a questionar a influência dos professores que tivemos na nossa formação profissional. Mesmo que os cursos de licenciatura enfatizem teorias mais modernas de ensino e aprendizagem, os professores acabam assumindo a posição de seus antigos professores. Observamos que a formação do professor não se da exclusivamente na licenciatura, mas durante toda a sua vida escolar e após a sua formação, na própria prática docente. As concepções sobre ensino e aprendizagem, sobre o papel da escola, do professor e do aluno, entre outras, podem ser questionadas através da retomada da história de vida de cada um dos professores.

Abstract: The goal of this study is to question the influence of our former teachers in our professional career as teachers. Although the teaching courses at University emphasize the modern theories of theaching and learning, frequently the attitudes of the new teachers in classroom are mirrored in the behavior of their former teachers. The analyses showed that not only the theacher's training occurs at University but during all the school life and after the graduation. The discussion about the histories of lives should be used to question our conceptions of learning and teaching, the role of the school, the teachers and the students, towards changes in education.