A new foaming technique for production of superabsorbents from carboxymethyl chitosan

A foaming technique was developed for production of superabsorbent polymers (SAP) from carboxymethyl chitosan (CMCS) with high, medium and low molecular weights. In this method n-pentane was used as a blowing agent due to low boiling point and immiscibility with water. n-Pentane was added to a warm aqueous solution of CMCS and boiled. CMCS was then gelled by adding the crosslinking agent glutaraldehyde and consequently n-pentane was captured inside the polymer network. The n-pentane was evaporated from this network while drying in oven. It resulted in stable foam that prevented the hydrogel from collapsing and the dried product had a porous structure with a high water-binding capacity (WBC). The effects of molecular weight of CMCS and its concentration, and the amounts of glutaraldehyde and n-pentane used, on WBC were investigated and optimized using response surface experimental design. The best result for WBC of foam-dried SAP was 107 (g/g) after exposing for 1 h in pure water and 60 (g/g) and 37 (g/g) after exposing for one min in pure water and 0.9% NaCl solution, respectively. The WBC of the SAP produced by the foaming technique was more than five times higher than the WBC of the oven-dried crosslinked CMCS.