Influencia del tiempo de almacenamiento en las propiedades estructurales de un almidón termoplástico de yuca (TPS)

Abstract

Changes in structural properties of thermoplastic cassava starch (TPS) under controlled humidity and temperature conditions were studied. The samples were dried at 60°C for 12 hours and stored at 25ºC and 54% relative humidity. The tensile and physicochemical properties at several time intervals were determined. An amorphous mass was obtained during plasticization process (corroborated by SEM, XRD and FTIR analysis). The XRD also shows evidence of resiual type C crystallinity and the formation of a new crystalline phase type VH due to the orientation induced by plasticization process. In a first aging stage, the tensile strength decreased and the breaking strain increased with time. In a second stage, the opposite behavior was obseved. During the entire period, the crystallinity index gradually increased, being this parameter determined from the FTIR bands intensities ratio (1047/1022 cm-1). These bands have been associated with crystalline and amorphous region respectively. These findings suggest that two opposite process (re-crystallization and plasticization) take place simultaneously during aging; the former predominates at longer times whereas the latter at shorter times. The re-crystallization (retrogradation) process tends to make the TPS stiffer while the plasticization process tends to soften it.