Hydrolysis effects on the water uptake of starch-g-glycidyl methacrylate (GMASt)/dimethylacrylamide (DMAAm)-based hydrogels for potential agricultural purposes

Abstract

This work assessed the effect of different hydrolysis periods on the properties of hydrogels based on 75 % w w^-1 of N,N'-dimethyl acrylamide (DMAAm) and 25 % w w^-1 of starch-g-(glycidyl methacrylate) (^GMASt). FTIR results confirmed the conversion of ester groups into carboxylic acids and carboxylates, besides forming a keto-enol tautomer due to the peeling reaction of starch. For DMAAm, the hydrolysis mostly converted amide into carboxylate groups. The morphology, thermal stability, and the mechanical properties of the predominantly amorphous matrices (as confirmed by XRD results) did not drastically change even after 10 days of hydrolysis in alkali media. However, the thermogravimetric analysis results suggested that DMAAm partially protected ^GMASt from the hydrolysis. The swelling degree of the matrix increased from (10.1 ± 2.1) g g^-1 to (61.9 ± 2.6) g g^-1 after 1 day of hydrolysis, but no statistical differences (at 95 % of significance) were observed for the matrices hydrolyzed for longer periods, confirming that the maximum hydrolysis occurred within 24 h. The results confirmed that the hydrolysis increased the water uptake of the ^GMASt/DMAAm-based matrices, making appealing for uses as a water retentor for agricultural purposes.

Keywords: Base-catalyzed reaction; Natural polymer; Water retaining system.