Unraveling Process–Structure–Performance Relationships in Bio-Based Chitosan and Alginate–Chitosan Capsules for Durable Antifungal Cotton Functionalization

Essential oil-loaded bio-based capsules have emerged as promising candidates for sustainable antimicrobial textiles; however, the relationships between processing conditions, capsule architecture, textile fixation, and functional performance remain poorly understood. In this study, chitosan and alginate–chitosan capsules encapsulating clove essential oil (CEO) were comparatively engineered to investigate the process–structure–performance relationships governing antifungal cotton functionalization. Two encapsulation strategies based on emulsion-assisted alkaline gelation and ionic gelation were optimized using Taguchi L18 experimental designs and response optimization to identify suitable processing conditions and target capsule characteristics. For the chitosan system, the selected formulation consisted of 0.5% chitosan, 5% acrylic acid, 1% Tween 80, 7% CEO, 1% NaOH, and a 2× dilution ratio, yielding a predicted capsule size of 259.539 nm and an intensity of 81.3945% with an overall desirability of 0.677991. For the alginate–chitosan system, the selected formulation contained 1% alginate, 0.5% chitosan, 7% CEO, 2% Tween 80, and a 30× dilution ratio, resulting in a predicted capsule size of 382.753 nm and an intensity of 93.0053% with a desirability of 0.736852. Particle-size analysis showed predominantly nanometric populations, with a bimodal distribution centered at approximately 230 nm for chitosan capsules and a trimodal distribution with a predominant population around 360 nm for alginate–chitosan capsules. The optimized capsule suspensions were applied to cotton fabrics using citric acid-assisted thermal treatment. ATR–FTIR analysis revealed spectral changes consistent with interactions between the capsule components, citric acid, and cellulose, while the treated fabrics exhibited improved retention after washing. Both encapsulated systems retained antifungal activity against Candida albicans, although the inhibition zones were lower than those obtained with free CEO, consistent with modified CEO accessibility and diffusion. Overall, the results establish a process–structure–performance framework linking formulation and processing conditions to capsule architecture, textile fixation, and antifungal functionality, providing a basis for the rational design of durable bio-based functional textiles.