Production of superabsorbents from fungal chitosan

Superabsorbent polymers (SAPs) were prepared from fungal chitosan through three steps of carboxymethylation, cross-linking, and freeze drying. The alkali-insoluble material (AIM) of the cell wall of zygomycetes fungus Rhizomucor pusillus was first pretreated with 72 mM sulfuric acid at room temperature to release the phosphates from the cell wall. The phosphate-free AIM was then either subjected directly to carboxymethylation, or treated with 72 mM sulfuric acid at 120 degrees C to extract and recover the fungal chitosan prior to carboxymethylation. The carboxymethylated derivative of pretreated AIM (CM-P-AIM) and carboxymethyl fungal chitosan (CM-f-CS) exhibited 50 and 100 % water solubility, respectively. Glutaraldehyde was subsequently added to aqueous mixtures of CM-f-CS and CM-P-AIM to cross-link the water-soluble fractions. These mixtures were then frozen at -20 degrees C and freeze dried. The water-binding capacity (WBC) of the final product obtained from CM-f-CS (30 % of AIM) was 77, 30, 33 and 45 g/g after 10 min of immersion in water, urine, 0.9 % NaCl and artificial blood solutions, respectively. The respective WBCs of the product obtained from CM-P-AIM (90 % of AIM) were 73, 22, 24 and 37 g/g at identical conditions. SEM micrographs indicated that the SAPs prepared from CM-f-CS and CM-P-AIM had porous sheet-like structures.