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 Nad 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.
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