DOE-based synthesis of gellan gum-acrylic acid-based biodegradable hydrogels: screening of significant process variables and in situ field studies

Abstract

The current study uses the free radical graft copolymerization of acrylic acid as a monomer, N,N-methylene-bis-(acrylamide) as a crosslinker and ammonium persulfate as an initiator to synthesise GG-cl-poly(AA) hydrogels based on gellan gum utilising response surface methodology (RSM). A full factorial design was used to obtain the greatest percent swelling (P_s), and key process variables were determined using the Pareto chart. To make the procedure cost-effective, a multiple regression model employing ANOVA projected a linear model with a maximum percentage swelling of 556 at the lowest concentration of all three studied factors. As a result, the sequential experimental design was successful in obtaining two-fold increases in the percentage swelling in a systematic way. An RSM-based central composite design was used to optimize the percentage swelling of the three most important synthesis parameters: initiator concentration, monomer concentration, and crosslinker concentration. The best process conditions are 7.3 mM L⁻¹ initiator, 44 μM L⁻¹ monomer, and 21.6 mM L⁻¹ crosslinker. The effective synthesis of GG-cl-poly(AA) was validated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, field emission scanning electron microscopy (FE-SEM), and ¹H-nuclear magnetic resonance. The swelling behavior of GG-cl-poly(AA) in water and saline solutions, as well as its water retention capability, was investigated. In comparison to distilled water, the swelling potential of optimized hydrogel was shown to be significantly reduced in saline solutions. The addition of GG-cl-poly(AA) significantly improved the moisture properties of plant growth media (clay, sandy, and clay–soil combination), implying that it has great potential in moisture stress agriculture. GG-cl-poly(AA) biodegradation was studied by soil burial and vermicomposting methods. The composting approach showed 89.95% deterioration after 22 days, while the soil burial method showed 86.71% degradation after 22 days. The synthesized hydrogel may be beneficial for agricultural applications because of its considerable degradation behaviour, strong water retention capacity, low cost, and environmental friendliness.