Xanthan gum in solution and solid-like state: Effect of temperature and polymer concentration

Abstract

The development and optimization of xanthan-based systems are closely related to its structure and the properties induced in the material which contains it. Considering this, the present work aimed to investigate the effect of temperature and polymer concentration on the rheological properties of xanthan gum (XG) aqueous solutions, and on morphology of corresponding films. Viscoelastic properties of the solutions with 0.4, 1.0 and 2.0 % XG have been studied in oscillatory and continuously shear regimes. A solid-like response over the entire studied frequency range was observed for investigated solutions. The Cox-Merz superposition of complex and apparent viscosities was evidenced only for 0.4 and 1.0 % XG solutions. The effect of XG content on yield stress of solutions was also discussed. The morphology of surface and cross-section of XG films, prepared by casting solution method, were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM) and polarized optical microscopy (POM). The morphological aspects at nanometric scale, investigated by AFM, highlighted the influence of the XG concentration on the film characteristics, the isotropy/anisotropy balance and the surface texture. SEM and POM microphotographs of film, obtained from 2.0 % XG solution, evidenced an ordered structure of polymer chains and birefringence, respectively.