Green and sustainable carboxymethyl cellulose-chitosan composite hydrogels: Effect of crosslinker on microstructure

The toxicity level of conventional hydrogels is considerably high for most applications. To date, very few studies on hydrogels synthesized using only safe materials and simple, reproducible processes are available in the literature. Moreover, critical information on hydrogels hydrolytic behavior and stability—important parameters to determine microstructure—is missing. Herein, new composite hydrogel matrices are developed using green, sustainable materials through a simple, reproducible low-temperature chemical method. Natural polymers (carboxymethyl cellulose and chitosan), crosslinkers (fumaric acid, citric acid, tartaric acid and zinc ion), and solvent (water) are used. The hydrogels are characterized for degree of crosslinking and microstructure parameters calculated using Flory Rehner equation. Bonding strength and stability of the microstructure are further assessed. With respect to the hydrolytic properties, it was found that CMC~FU~CSN exhibits well-defined microstructure (155% swelling, 79% water absorbency and 82% gel fraction) superior to the other crosslinked hydrogels and the non-crosslinked composite, CMC~CSN. However, its gel fraction was within the same range as CMC~CSN (332% swelling, 91% water absorbency and 79% gel fraction). Other characterization results confirm that CMC~FU~CSN has the optimum microstructure (3 nm mesh size, 261 g/mol molecular weight between crosslinks and 0.01 μmol/cm³ effective crosslinking density), thermal stability (2% mass loss at 50 °C, 3% at 100 °C against 6% at 50 °C, 8% at 100 °C for CMC~CSN), semi-crystalline structure and chemical properties making it preferred over CMC~CSN as a promising green and sustainable hydrogel matrix.