In the current work, we studied dc conductivity and its relaxation in glycerol-plasticized starch membranes at various concentrations using impedance spectroscopy in frequency ranges between 20 Hz and 3 MHz and temperature ranging from 303 K to 423 K. We observed thermally activated dc conductivity following the Arrhenius model: ln s ¼ ln s o À E s =k B T , where the activation energy, E σ , diminished as glycerol increased. Non-Debye relaxation phenomena were observed in the actual portion of the conductivity as a function of the frequency, s 0 w ð Þ $ w n n % 1 ð Þ. Also, the symmetry of the relaxation peak observed in the imaginary part of the electric module remained unaltered as a function of temperature and glycerol content in the membranes, corresponding to a constant exponent, β=0.80±0.02, if we assume the ФðtÞ ¼ exp À t=t ð Þ b h i correlation function in the ionic transport. The angular velocity, ω p , registering the maximum peak, M ″ max , was fitted to the Arrhenius model, ln w ¼ ln w o À E w =k B T , finding great similarity between E ω and E σ values for each sample, indicating that the corresponding ionic processes have the same origin, in other words, due to the correlated jump of the charge carriers. The independence found between n and β indicates that the correlation processes or cooperative effects among ions in these materials deviate from the empirical description expressed by Ф(t). However, these processes were identical when varying temperature glycerol content in the membranes, as suggested by the M″(ω) spectra.

In this work we study the effect of different reducing agent (chitosan, starch and sugars) on to synthesis of silver (AgNPs) and gold (AuNPs) nanoparticles by reduction of silver nitrate (AgNO3) and chloroauric acid (HAuCl4), respectively. The plasmon absorption peak between 419 - 434 nm, measured using a UV-Vis spectrophotometer indicates the existence of AgNPs, this reaction was favored by the increase of temperature with optimal results at 90°C. Synthesis of AuNPs was only obtained using chitosan as reducing agent, the use of solutions of starch and sugars allows the reduction of the gold salt present in the chloroauric acid, however the low pH of the solutions creates thermodynamic instabilities for the AuNP synthesis, due to low repulsive force for colloid stability.

A b s r a c t. 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 seconddegree 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.K e y w o r d s: glycerol, potato starch solutions, pseudoplastic behaviour, rheological models

A b s t r a c t. The rheological behaviour of vinasses derived from sugar cane was studied as a function of time (0 and 600 s), soluble solids content (44 and 60 °Brix), temperature (10 and 50°C), and shear rate (0.33 and 1.0 s -1 ). The results indicated that vinasses were time-independent at 25°C, where shear stress values ranged between 0.01 and 0.08 Pa. Flow curves showed a shear-thinning rheological behaviour in vinasses with a flow behaviour index between 0.69 and 0.89, for temperature between 10 and 20°C. With increasing temperature, the flow behaviour index was modified, reaching values close to 1.0. The Arrhenius model described well the thermal activation of shear stress and the consistency coefficient as a function of temperature. Activation energy from the Arrhenius model ranged between 31 and 45 kJ mol -1 . Finally, the consistency coefficient as a function of the soluble solids content and temperature was well fitted using an exponential model (R 2 = 0.951), showing that the soluble solids content and temperature have an opposite effect on consistency coefficient values.