Caracterização reológica da goma xantana: influência de íons metálicos univalente e trivalente e temperatura em experimentos dinâmicos

Abstract

Resumo: As propriedades dinâmicas das soluções aquosas de goma xantana com e sem adição de NaCl ou Al 2 (SO 4 ) 3 .18H 2 O foram medidas em um reômetro de deformação controlada aplicando ciclos de aquecimento e resfriamento. O tempo de relaxação decresceu com o aumento da temperatura; no entanto, este tempo aumentou com a adição de sal nas soluções de 0,5% em peso de goma xantana, mas diminuiu com a adição de 1%. Durante o aquecimento das soluções de goma xantana pura ocorreu uma mudança de conformação a 51 °C, e durante o resfriamento foi observada a formação de duas estruturas: entre 86 e 47 °C e abaixo de 47 °C. Com a adição de sal não houve mudança conformacional durante o aquecimento, enquanto no resfriamento duas estruturas foram novamente observadas, mas para faixas de temperatura diferentes. Palavras-chave: Xantana, mudança conformacional, reologia, gel, viscoelasticidade. Rheological Characterization of Xanthan Gum: Influence from Univalent and Trivalent Metallic Ions and From the Temperature in Dynamic ExperimentsAbstract: The dynamic rheological properties of water xanthan gum solutions with and without the addition of NaCl or Al 2 (SO 4 ) 3 .18H 2 O were measured in a strain controlled rheometer applying heating and cooling cycles. The terminal relaxation time decreased with increasing temperature. This time increased with the addition of 0.5 wt. (%) of salt, but decreased when 1 wt. (%) was added. During heating a conformational change occurred at 51 °C and upon cooling two structures were observed between 86 and 47 °C and below 47 °C. When salt was added there was no conformational change during heating, but the two structures again appeared during cooling, though at different temperature ranges.

Rheological assessment of the interaction between hydrophobic nanoclay and xanthan gum in saline environment, for application in drilling nanofluid

“…In parallel, XG solutions present a decrease in viscosity and approximation to Newtonian flow with an increase in temperature due to the change in conformation: XG in solutions without counterions, presents a helical conformation due to solvation and consequent repulsion of triglycerides, a phenomenon that favors the expansion of macromolecules, their separation into smaller structures and the formation of hydrogen bonds, however, given an anionic nature, the formation of a network of ligands has a weak interaction [Wyatt and Liberatore, 2009;Rocherfort and Middleman, 1987]; with increasing temperature, the helical structure changes to a coil structure [Rocherfort and Middleman, 1987] or disordered between the range of 47 to 51°C [Luporini and Bretas, 2011], which interferes with its rheology by decreasing its viscosity and making it more Newtonian [Benyounes et al, 2010;Speers and Tung, 1986], and when cooled, it changes its shape from disordered to fractured helix, which allows the formation of the network structure.…”

“…In the presence of counterions, this conformational transition does not occur in the temperature range adopted in this experiment, the helical structure remaining during heating and the fractured helix and consequent formation of a network with cooling [Wyatt and Liberatore, 2009;Luporini and Bretas, 2011]. Table 10 presents the Doehlert Matrix applied to the experimental planning of this stage.…”

“…The Minimum Stress does not present sensitivity to temperature variation, justified by the concentration of the salts present in the sample, what preserved XG from degradation [Xie and Lecourtier, 1992;Luporini e Bretas, 2011;Speers and Tung, 1986], as there is also possible early dissociation of NA sheets by the state particulate and, given the polarity promoted by the surfactant, interaction with the biopolymer [Benyounes et al, 2010] or the formation of the network, or even the flocculation of the clay with the increase in temperature [Xie and Lecourtier, 1992;Santos, 2000].…”

Use of green coconut shells as an alternative substrate for the production of xanthan gum on different scales of fermentation

“…Thus the petroleum industry does not use large amounts of xanthan on account of its high cost, and ends up using other polysaccharides derived from plants or synthetic polymers, which are cheaper but have less specific properties for the tertiary extraction of petroleum from deep wells [2,6] . Xanthan gum is imported for about US$ 10-18/Kg, but if manufactured in Brazil from sucrose, the cost is estimated to decrease by 40 to 60% [2,7] .…”

Biomateriais binários de quitosana/amido e quitosana/gelatina em L-ácido lático

“…As Figuras 42 e 43 mostram a dependência dos módulos elásticos G' e viscoso G'' em função da temperatura para os géis QGL e QAL, na frequência de 1,0 Hz. As curvas mostraram que a baixas temperaturas (até aproximadamente 50ºC), todos os géis apresentaram o mesmo comportamento com G"> G' e tanto os valores de G' quanto de G" decrescem ligeiramente com a temperatura, o que é comumente observado para polímeros em solução (LUPORINI et al, 2011). Após a temperatura de gelificação das amostras há o aumento de G' e G'' com a inversão dos parâmetros…”