Ca²+ sorption on regenerated cellulose fibres

Area of Science:

• Materials Science
• Textile Chemistry
• Analytical Chemistry

Background:

• High calcium content in cellulose materials poses challenges in pulp processing, textile treatments, and consumer use.
• Cellulose's carboxyl groups enable it to bind calcium ions (Ca2+), relevant for food, medical, and textile applications.

Purpose of the Study:

• To investigate the calcium ion binding capacity of regenerated cellulose fibers.
• To determine the mechanism and stoichiometry of Ca2+ binding to cellulose carboxyl groups.
• To identify the counter ion involved in charge neutralization during Ca2+ sorption.

Main Methods:

• Methylene Blue sorption method to quantify carboxyl group content.
• Alizarin complex formation to demonstrate Ca2+ binding.
• Potentiometric titrations to identify counter ions.

Main Results:

• Regenerated cellulose fibers (lyocell, viscose) exhibit significant Ca2+ binding capacity, limited by carboxyl group content (15 mmol/kg for lyocell, 20 mmol/kg for viscose).
• The molar ratio of carboxylic groups to bound Ca2+ ions is 1:1, indicating one Ca2+ ion binds per carboxyl group.
• Ca2+ sorption results in a net positive charge on cellulose, with bicarbonate (HCO3-) identified as the counter ion for charge neutralization.

Conclusions:

• Regenerated cellulose fibers effectively bind Ca2+ ions via their carboxyl groups.
• The binding process involves a 1:1 stoichiometry between carboxyl groups and Ca2+ ions.
• Bicarbonate ions act as counter ions, forming a COO-Ca2+HCO3- complex within the cellulose structure.