Cation release from different carboxymethyl cellulose hydrogels

Biodegradable hydrogels have great potential in agriculture. In this study, hydrogel prototypes of biodegradable slow-release fertilizers were formulated by a Schiff base reaction between dialdehyde carboxymethyl cellulose and gelatin. The release behavior of iron cations from these carboxymethyl cellulose-based hydrogels with different degrees of substitution was studied. The analyses of the relation between correlation length of the cross-linked hydrogels and the degree of substitution, i.e., the amount of negatively charged positions in the hydrogels, allowed to determine the influence of structure and electrostatic interaction on cation release kinetics, which was successfully described by Peleg’s Model. The hydrogel with the lowest degree of substitution reveals the slowest release of cations due to the smallest correlation length. These results demonstrate that the correlation length is dominant for the release of divalent cations. Moreover, this also shows the potential of the DACMC-Gelatin hydrogels as matrix for slow-release fertilizers.