Rubén Antonio Vargas

Influence of Glycerol and Temperature on the Rheological Properties of Potato Starch Solutions

Abstract Effects of temperature and glycerol concentration on rheological properties of potato starch solutions were investigated. The flow behaviour (shear stress against shear rate) was fitted to various models: power law, Herschel-Bulkley, Bingham, modified Bingham and Casson models. However, it was found that the Herschel-Bulkley model describes better the flow behaviour observed at various temperatures and glycerol concentrations, for flow behaviour index values between 0.44 and 0.78, typical of pseudoplastic solutions. The effect of glycerol concentration on each of the fitting parameters for Herschel-Bulkley model was well modelled by a second-degree polynomial at various temperatures. The simultaneous influence of glycerol concentration and temperature on shear stress could be represented empirically by a second-degree polynomial function that includes linear coupling between concentration and temperature. Finally, the variation of the consistency coefficient with both temperature and glycerol concentration was well described by an exponential expression, with an activation energy value of 2.78 kJ mol-1. The results indicate that both glycerol content and temperature have the effect of diluting potato starch solutions.

CARACTERIZACION ESPECTROSCOPICA Y ANALISIS TERMICO DE LOS COMPLEJOS TRIFENILFOSFINA-RUTENIO(II) CONTENIENDO EL LIGANDO 2,6-DIMETILPIRAZINA Y OTROS N-HETEROCICLICOS

Los complejos sintetizados [RuCl2(2,6-dmpz)2(PPh3)2] y [RuCl2(CO)(N-het)(PPh3)2], (donde N-het son 2,6-dimetilpirazina (2,6-dmpz), Imidazol (Imz) y pirazina (pz)) PPh3 = trifenilfosfina, se sintetizaron a partir de RuCl2(PPh3)3 y un ligando N-heterociclico. Estos complejos se caracterizaron por tecnicas espectroscopicas. Para el complejo [RuCl2(2,6-dmpz)2(PPh3)2] el espectro Ir indica que los cloros se encuentran en posicion cis. El espectro electronico de los complejos presenta intensas bandas de transferencia de carga, asignadas a las transiciones de los orbitales dp llenos del rutenio a los orbitales pp * vacios de los anillos N-heterociclicos. Los estudios termicos de DSC y TGA para los complejos del tipo diclorocarbonil(N-heterociclico)bis(trifenilfosfina)rutenio(II), donde los N-heterociclicos son 2,6-dmpz, Imz y pz, indican que la estabilidad termica de los complejos depende de la nucleofilidad del ligando nitrogenado.