<p>Bio-Hybrid Poly(Potassium Acrylate)-Grafted-Guar Gum (PKA-g-GG) Hydrogels: A Sustainable "Molecular Armoring" Approach to Scale Mitigation in Closed-Loop Water Systems</p>

Background: The intensification of water recovery in closed-loop systems, such as NASA’s Brine Processor Assembly and high-pressure industrial boilers, is fundamentally limited by mineral scaling. Conventional synthetic anti-scalants often suffer from thermal degradation at temperatures exceeding 150°C, leading to hardware fouling and increased corrosivity. Objective: This study investigates the synthesis and performance of a thermally resilient bio-hybrid hydrogel, poly(potassium acrylate)-grafted-guar gum (PKA-g-GG). The research characterizes the "molecular armoring" effect-defined as a synergistic protective mechanism where dense anionic PKA grafts sequester cations through multidentate chelation while the bulky galactomannan backbone provides steric hindrance against mineral nucleation and lattice growth. Methods: Utilizing an aqueous-phase graft polymerization pathway with a potassium persulfate (K2S2O8) initiation system, PKA-g-GG was synthesized and validated via Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis, and differential scanning calorimetry. Scale inhibition was quantified through complexometric ethylenediaminetetraacetic acid titration and Atomic Absorption Spectroscopy. Electrochemical Impedance Spectroscopy (EIS) was employed to characterize the polarization resistance (Rp) and the electrical double-layer architecture on aluminium substrates under accelerated scaling conditions (500 ppm CaCO3). Results: FTIR confirmed successful grafting with a prominent, broad carbonyl (C=O) peak at 1715-1750 cm-1. Thermal analysis revealed structural stability up to an onset of 280°C. At an optimal inhibitor concentration of 20 ppm, the bio-hybrid hydrogel PKA-g-GG achieved a maximum scale-inhibition efficiency of 43.08 ± 1.10%. EIS elucidated the interfacial protection mechanism, where a significant reduction in polarization resistance (Rp) from 794.5 to 498.4 Ω ⋅ cm2 was observed in 500 ppm CaCO3 environments. This confirms that the hydrocolloid prevents scale adhesion through a synergistic dual-action mechanism of chelation and crystal lattice distortion - a phenomenon defined here as "molecular armoring." Conclusion: The PKA-g-GG hydrogel represents a sustainable, technically competitive alternative for scale mitigation, supporting the >98% water recovery threshold required for NASA’s long-duration space life support and high-heat flux industrial applications.