RESUMEN El cuidado del medioambiente y el uso responsable de los recursos, ha promovido investigaciones con diferentes biopolímeros que permitan el desarrollo de nuevos materiales que puedan ser empleados en empaques para alimentos. Entre estos biopolímeros se encuentra la fibroína de seda (FS), que representa cerca del 70% de la fibra de seda y puede ser obtenida a partir de capullos de primera calidad o de los desperdicios generados en la producción serícola. En el desarrollo de empaques de alimentos con FS, se pueden dar dos alternativas de producción, una en la que la FS puede ser funcionalizada por otros componentes, y otra en la que se incluye la FS como componente funcional modificando otros biopolímeros. La FS puede conferirle al material de empaque ciertas propiedades, como: aumento de la permeabilidad de oxígeno, resistencia a la rotura y una mayor velocidad de degradación del biopolímero. Este artículo se centra en cuatro temas principales: empaques, biopolímeros en empaques, FS y finalmente, la FS en empaques para alimentos.

ABSTRACT Environmental protection and responsible use of resources, have promoted research of different biopolymers allowing to develop biodegradable materials which can be used in food packaging. Among these biopolymers is silk fibroin (SF), this protein represents nearly 70% of the silk fiber and it can be obtained from high quality cocoons or from waste generated in the silk industry. In the development of food packaging with SF, there are two possible alternative of production, one in what the SF can be functionalized by other components and another in which, the FS is included as functional component modifying other biopolymers. In the case of food packaging, the SF can concede desirable properties to the package such as an increase in oxygen permeability, more tensile strength and a higher biopolymer degradation rate. This paper is focused on four main topics: packaging, biopolymers in packaging, SF and finally, the SF in food packaging.

Depth sensing indentation study was conducted in a Fischerscope H100V machine, equipped with a Vickers indenter with a tip roundness of approximately 1330 nm. Tests were carried out on soda-lime glass, fused silica, sapphire, aluminum (1100 alloy), high alloyed steel, titanium and copper. The widely used iterative method of Oliver and Pharr was unsuccessful in the attempts to analyze machine compliance and indenter area function. Therefore, an alternative procedure was adopted. The alternative procedure is based on the ratio between maximum load and unload stiffness squared, Pm/Su². It was found that this procedure, which is not iterative, gives good results. A careful study of the Pm/Su² ratio, lead us to conclude that the Fischercope machine has a low compliance which depends on the sample mounting. This low compliance in conjunction with the recent discovery of the dependence of beta factor on the tip roundness/maximum depth ratio, which appears in the relation between contact stiffness and contact area, explains why the iterative method does not converge. However, variations in beta and machine compliance produces deviation on the hardness and elastic modulus lower that 6% with respect to expected values for the materials and the machine studied in this work.