Influencia do tamanho de particulas no comportamento reologico da polpa de jabuticaba. / The influence of particles size on rheological behavior of jaboticaba pulp.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The influence of particle size on rheological behavior of jaboticaba pulp was evaluated in this study. Particle size distribution (PSD) of the pulp was evaluated using laser diffraction, which showed a monomodal distribution with mean diameter close to 330um. Jaboticaba pulp was centrifuged for serum separation. Particles were then separated through wet sieving into different fractions (mean diameter of 64, 120, 200, 302,5, 390, 462,5, 550, 655 and 855um), which were mixed to the serum at the same volume fraction as the whole pulp (before centrifugation). Rheological properties were measured, at 25 oC, on a stress-controlled rheometer, equipped with grooved stainless-steel parallel-plate, using a 2,0 mm gap. Rheological characterization of jaboticaba pulp (both whole and reconstituted samples) showed a good fit to the Herschel-Bulkley model. Increase of particle size led to an increase on viscosity of reconstituted samples, which were always higher than viscosity of whole pulp. At low shear stress, whole pulp and reconstituted samples with 64 to 302,5um particles behaved as weak gel. Frequency sweep of reconstituted samples were fit to a 4-element Maxwell model, showing an increase in G0 values and no influence on the relaxation time as particle size increased. Yield stress (o0) evaluated by different methods (flow curve extrapolated to infinite apparent viscosity and to zero shear rate, and linearity limit of storage modulus on oscillatory tests) were compared. Usually, o0 increased linearly with increase of particle size, and the lower values of yield stress were obtained from oscillatory measurements. However, a decay of yield stress values was observed in samples constituted of particles with 655 and 855um when such data was obtained from flow curves. This result was attributed to sedimentation effects. Such a behavior was not observed in oscillatory measurements, indicating a better structure maintenance and showing the importance of rheological characterization at large and small deformations.

ASSUNTO(S)

jaboticaba viscoelasticity jabuticaba viscoelasticidade rheology atomização particle particulas reologia particulas atomization

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