Gelation kinetics of alginate chains through covalent bonds

Gelation kinetics of polymer chains through covalent bonds depends on many variables and affects many applications. Here we study the gelation kinetics of alginate chains through crosslinkers adipic acid dihydrazide (AAD), with coupling reagents 1-ethyl-3-(3-dimethylaminopropyl) (EDC) and N-hydroxysuccinimide (NHS). We use the rate equation of the reaction to calculate the extent of reaction, and use the Flory-Stockmayer theory to calculate the gelation time. The model predicts the gelation time as a function of the concentration of alginate, crosslinkers, and coupling reagents, as well as the functionality of an alginate chain and the rate constant of the reaction. Given an aqueous solution, we conduct rheological tests to measure the storage and loss moduli as functions of time, and determine the gelation time by the time when the storage modulus equals the loss modulus. The gelation times so determined for solutions of various compositions agree well with those predicted by the model. This combination of the model and experiments provide a practical approach to the design of gelation kinetics for applications. (C) 2020 Elsevier Ltd. All rights reserved.