Synthesis and Characterization Chitosan Cryogels Modified by Tripolyphosphate and Tannic Acid

In the present study, we prepared new cryogels based on the biopolymer chitosan (CH). We used tripolyphosphate (TPP) and tannic acid (TA) as eco-friendly crosslinking agents. TA improves the function of cryogels because it has a polyphenolic structure with an affinity for metal ions, and confers antimicrobial and antioxidant properties. Our objective in the present research was to determine the optimum combination of chitosan, TPP, and TA. The cryogels were synthesized in two stages: (1) high-speed homogenization (13,500 rpm) and freezing at −15 °C to prepare CH-TPP cryogels; and (2) synthesis of CH-TPP-TA by immersion in a TA solution and freeze-drying. We characterized the cryogels by scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FT-IR), and mercury porosimeter. The swelling properties and water uptake capacities of the cryogels were determined. The IR spectrum of CH-TPP-TA proved that TA had interacted with the chitosan by forming hydrogen bonds. TA strengthened the chitosan gel matrix, increased pore homogeneity, shortened the swelling equilibrium time, and increased porosity. The combination of 1 wt% chitosan, (2.5, 5, or 7.5 wt%) TPP, and 1 wt% TA produced cryogels of >90% porosity with pores of 26–57 μm. The properties of the CH-TPP-TA cryogels qualify them for use in several application fields, such as water treatment, waste handling, biomedicine, and bioengineering.