Linear and non-linear flow behavior of welan gum solutions
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Rheological and microstructural properties of welan gum aqueous solutions were studied as a function of polymer concentration in the 0.2–0.6% (m/m) range at fixed temperature 20 °C. Welan gum is an exopolysaccharide produced by Sphingomonas sp. All the systems exhibited a shear thinning and weak gel–like behavior whose parameters were well adjusted to a power law with the concentration. Furthermore, time-concentration superposition methods were carried out to obtain two master curves, one from the flow curves and the other from the mechanical spectra, which made it possible to extend the accessible experimental range. The non-linear viscoelastic properties were also studied by means of parallel superposition tests. The superimposed shear stress induced a change from weak gel to entangled solution behavior. This latter flow behavior is characterized by a frequency crossover that has been shown to have a linear dependence on the superimposed steady-state shear rate. Finally, Cryo-SEM images revealed a network with numerous junction zones between polymer chains.
KeywordsParallel superposition Welan gum Master curve Cryo-SEM
The authors are grateful to CP Kelco for providing materials for this research, to Servicios Centrales de Investigación (CITIUS), Universidad de Sevilla, and to Dr. Carlos Gracia (TA instruments, Spain).
The authors received financial support (Project CTQ2015-70700-P) from the Spanish Ministerio de Economía y Competitividad and from the European Commission (FEDER Programme).
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