Adipic acid, which is nontoxic, was used to dissolve chitosan. The chitosan/adipic acid solution was used to prepare chitosan membrane. After being heated at 80100 degrees C, the membrane was in situ chemically crosslinked by adipic acid, as verified by Fourier transform infrared and wide-angle X-ray diffractometer analysis. The crosslinked membrane did not collapse even without treatment in alkaline solution. In addition, the in situ crosslinking reaction was studied. The crosslinking degree (CLD) was quantitatively calculated based on the mass of water produced. The results showed that CLD was positively related to both heating temperature and time. Results of kinetic of crosslinking reaction suggested that the amidation was in agreement with the first-order rate equation and that the temperature effect could be described with the Arrhenius equation. The results of weight loss of chitosan membrane in phosphate-buffered solution (pH = 7.4) indicated that the best water resistance of chitosan membrane was obtained at 90 degrees C. In brief, a straightforward, nontoxic, environment-friendly, and economical chemically crosslinking approach has been developed for chitosan materials. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013