Synthesis and swelling behavior of xanthan-based hydrogels

Area of Science:

• Polymer Chemistry
• Materials Science
• Biomaterials Engineering

Background:

• Xanthan gum is a natural polysaccharide with potential applications in hydrogel development.
• Crosslinking is essential for creating stable hydrogel networks with tunable properties.
• Understanding water diffusion is crucial for predicting hydrogel performance in various applications.

Purpose of the Study:

• To investigate the effect of citric acid on xanthan hydrogel crosslinking via esterification.
• To analyze the swelling behavior and water diffusion mechanisms in the synthesized hydrogels.
• To explore the influence of pH and salt concentration on hydrogel swelling properties.

Main Methods:

• Xanthan hydrogels were synthesized through esterification at 165 °C, with and without citric acid.
• Swelling degree was measured to assess crosslinking density.
• Tensiometry was employed to study water diffusion kinetics and mechanisms (quasi-Fickian, Fickian, Anomalous).
• The impact of varying pH and salt concentrations on swelling was evaluated.

Main Results:

• Citric acid significantly increased hydrogel crosslinking density, indicated by lower swelling.
• Water diffusion initially followed a quasi-Fickian mechanism, transitioning to Fickian or Anomalous based on hydrogel composition.
• Increased pH led to higher swelling due to electrostatic repulsion and ester bond hydrolysis.
• Salt ions affected equilibrium swelling through interactions with polymer chains, water's EPA/EPD, or osmotic gradients.

Conclusions:

• Citric acid is an effective crosslinking agent for xanthan hydrogels, improving network stability.
• The hydrogels exhibit complex water diffusion behaviors influenced by composition and environmental conditions.
• Hydrogel swelling is sensitive to pH and ionic strength, offering possibilities for controlled release applications.