Exploring the hydrogen-bond structures in sodium alginate through two-dimensional correlation infrared spectroscopy

Area of Science:

• Materials Science
• Polymer Chemistry
• Spectroscopy

Background:

• Sodium alginate (SA) is a biopolymer with significant hydrophilicity.
• Hydrogen bonding plays a crucial role in the structural integrity and properties of SA films.
• Understanding heat-induced changes in SA is vital for its applications.

Purpose of the Study:

• To investigate the evolution of heat-induced hydrogen bonding in sodium alginate films.
• To elucidate the role of water molecules in the hydrogen bonding network of SA.
• To characterize the structural changes occurring in SA upon heating.

Main Methods:

• Fourier Transform Infrared (FTIR) spectroscopy was the primary analytical technique.
• Perturbation Correlation Moving Window (PCMW) technique was employed for detailed analysis.
• 2D Correlation Spectroscopy (2Dcos) was utilized to analyze spectral changes.

Main Results:

• At room temperature, water-SA hydrogen bonds dominate, disrupting SA's internal bonding.
• Upon heating (30-60°C), water evaporation leads to the formation of inter/intra-molecular SA hydrogen bonds (e.g., O3H3…O5, O2H2…O=C-O⁻).
• Further heating (60-170°C) progressively breaks both SA-SA and SA-water hydrogen bonds, yielding free COH and COO⁻ groups.

Conclusions:

• Heat significantly alters the hydrogen bonding network in sodium alginate films.
• The transition involves initial water removal followed by the breaking of SA's internal hydrogen bonds.
• These findings provide insights into the thermal stability and degradation mechanisms of SA.