INTEMA   05428
INSTITUTO DE INVESTIGACIONES EN CIENCIA Y TECNOLOGIA DE MATERIALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Biodegradable nanoreinforced films
Autor/es:
M. PEREDA; N.E. MARCOVICH; M.I. ARANGUREN; A. DUFRESNE
Lugar:
Pretoria
Reunión:
Conferencia; 11th International Conference on Frontiers of Polymers and Advanced Materials, XI ICFPAM; 2011
Resumen:
Biodegradable films from renewable natural products are not only degraded readily after their disposal, but can also extend the food shelf life, thus improving the quality of food. Caseinate derived film wraps are able to partially replace some conventional synthetic packaging materials used to preserve and protect foods, being in addition renewable and biodegradable materials [1]. Chitosan is available from waste products of the shellfish industry [2] and its importance resides in its antimicrobial properties in conjunction with its cationicity and its film-forming properties. Moreover, chitosan, bearing positively charged groups, can interact and form three- dimensional networks with molecules containing opposite charges, like caseinate [3]. Finally, to improve mechanical and barrier properties without decreasing desirable properties (i.e. extensibility) nano-reinforcements can be added to the film forming solutions to obtain composite films. In this work, nano-reinforced films aimed for food packaging applications, made from chitosan and/or sodium caseinate, using glycerol as plasticizer, were prepared by casting from aqueous suspensions. To maintain the desirable matrix properties (i. e. relatively high elongation at break and transparency) and to keep the bio-degradability and potential edibility of the material, very low concentrations (up to 3 wt%) of nano-cellulose crystals prepared from acid hydrolysis of microcrystalline cellulose were selected as the reinforcing phase. FSEM observations performed on the surface of the samples allowed confirming the homogeneity of filler dispersion in all cases. Dynamic mechanical analysis performed on chitosan-based films revealed that their thermal transitions are almost not affected by the addition of nano-cellulose. Chitosan is a semicrystalline polymer, and the presence of crystalline portions could avoid that the amorphous part of the matrix got in contact with the nanofibers. Nevertheless, when chitosan-caseinate hybrid is used as matrix, the addition of only 0.5 % of nanocellulose results in a shift of the α-transition towards higher temperatures (from -54ºC to -41ºC). While chitosan is a semicrystalline polymer, chitosan-caseinate hybrid is an amorphous one, which facilitates its interaction with nanofibers. By increasing nanofiber concentration above 0.5%, Tg values decreased again. This last effect is due to fibers aggregation and led to a reduced contact surface to interact with the matrix. In the same way, the storage modulus of composites based on chitosan was always higher than the corresponding to chitosan-caseinate hybrids, with almost no differences related to cellulose concentration. In the second case (hybrid films) the storage modulus of composites was higher than that of the neat matrix, without a clear trend with nano-filler content.