Enzymatic gelation to prepare chitosan gels: Study of gelation kinetics and identification of limiting parameters for controlled gel morphology.

Chitosan gels with well-controlled morphology were prepared by an enzymatic chitosan gelation process using in-situ production of ammonia through the urea enzymatic hydrolysis by urease. The reaction kinetics were studied by four complementary methods (rheological, colorimetric, flowing and pH-metric measurements) to define an advanced gelation pH (and the corresponding advanced gelation time) enabling to obtain homogeneous chitosan gels with well-controlled morphology and strong enough to be suitable for a future membrane preparation. A comparative study of chitosan gelation kinetics in water and aqueous chitosan solution highlighted differences mainly related to ammonia consumption when chitosan was present. The key parameters evidenced for the control of the gelation kinetics were the temperature and the urease concentration. The operating parameters required to elaborate gels with sufficient mechanical resistance to be handled from 2.5% w/v chitosan concentration were defined: a 3.5umL-1 urease concentration, a 75mM urea concentration and a temperature of 5°C.