PREPARATION OF CARBOXYMETHYL CELLULOSE AND POLYVINYL ALCOHOL (CMC/PVA) HYDROGELS USING FREEZE−THAW PROCESSES FOR ADSORPTION OF Zn2+ AND Cu2+

"The preparation of carboxymethyl cellulose and polyvinyl alcohol (CMC/PVA) composites is proposed in the presentwork. The CMC/PVA hydrogels were prepared using freeze−thaw processes. The effects of freezing time and of thenumber of freeze−thaw cycles on the swelling ratio and gel fraction of achieved hydrogels were evaluated usingresponse surface methodology. The multiple regression analysis suggested second order polynomial equations asmodels for predicting changes of the studied hydrogel characteristics by selected process variables, with relatively highcoefficients of determination (R2 > 0.82). The numerical optimization suggested that freezing the polymer solutions for5 h and repeating the freeze−thaw process for 5 times would give the most desirable hydrogels with highest eitherswelling ratio or gel fraction. Remarkably, the ion adsorption studies showed that the adsorption of Cu2+ and Zn2+ ionsby the hydrogels obeys zero order kinetics and the high capability of the produced optimum hydrogels to adsorbselected ions from synthetic waste was confirmed."