<![CDATA[Background: Nutrient losses from conventional fertilization have increased the need for biodegradable hydrogel matrices that improve water retention and support controlled-release fertilizer (CRF) systems. This study investigated the effects of pH on the early-stage swelling kinetics of chitosan-based hydrogels, identified the most stable formulation, and examined the relationship between the degree of deacetylation (DD) and swelling performance. Methods: A quantitative experimental design was applied to four formulations, namely ChGu, ChG, ChPu, and ChP, under acidic, neutral, and alkaline conditions. Swelling was measured over 120 minutes with replicate measurements. The analysis included the swelling ratio (SR), maximum swelling ratio (Max SR), area under the curve (AUC), net swelling change (ΔSR), means, standard deviations, statistical comparisons, and regression analysis. Findings: pH markedly influenced the swelling behavior of all formulations. Neutral conditions produced the highest average SR values, with ChP showing the best performance (86.4), followed by ChG (67.6), ChGu (63.8), and ChPu (30.4). ChP also recorded the highest Max SR (124) and AUC (11,100), while ChG reached a Max SR of 110 and an AUC of 9,150. These findings indicate that both formulations had greater expansion capacity and more sustained swelling. In contrast, alkaline conditions caused deswelling in most samples, as indicated by negative SR values. The relationship between DD and swelling performance was weak (R² = 0.14), indicating that hydrogel structure, formulation composition, environmental pH, and early kinetic transitions were more influential than DD alone. Conclusion: Neutral pH provided the most favorable swelling conditions, and ChP demonstrated the strongest overall performance. Novelty/Originality of this article: This study proposes Max SR, AUC, ΔSR, and dynamic transition intervals as integrated early-stage indicators for screening biodegradable chitosan hydrogels for CRF applications.]]>
