Direct Chitosan Extraction Using Natural Deep Eutectic Solvent for Controlled Release Fertilizer Fabrication

Mohd Hazwan, Bin Hamdi (2025) Direct Chitosan Extraction Using Natural Deep Eutectic Solvent for Controlled Release Fertilizer Fabrication. Masters thesis, Universiti Malaysia Sarawak.

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Abstract

Chitosan is a biopolymer commonly found in hard exoskeleton shell animal such as shrimp, snail shell, and crab. Conventional extraction of chitosan biopolymers from natural sources typically involves the use of hazardous chemicals and lengthy processing times. This study presents a sustainable approach for the direct extraction of chitosan from snail shells using a natural deep eutectic solvent (NADES) system. The NADES was formed by combining acetogenin extracted from graviola (hydrogen bond donor) with choline chloride (hydrogen bond acceptor) at various molar ratios and synthesis temperatures. The NADES was characterized for polarity, density, surface tension and DSC, while chitosan extracted was analysed for moisture and ash content, TGA, FTIR-ATR, contact angle, viscosity, XRD, and SEM. The chitosan produced through this method exhibited degree of deacetylation in range of 87.6 - 93.3% and molecular weight in range of 40 - 115 kDa, with a fiber-like morphology. This extracted chitosan is comparable properties to commercial chitosan. The extracted chitosan was further applied as co-polymer for encapsulation of urea with alginate and calcium chloride as crosslinker. Response surface methodology (RSM) was applied to determine the optimal variables (molecular weight of chitosan, amount of alginate, and crosslinker) for achieving optimum encapsulation efficiency (EE%) and sustained release of urea (UR%) fertilizer from chitosan-alginate hydrogel beads. Results shows that the ideal formulation for attaining high EE% and UR% is using low molecular weight chitosan (40 kDa), a moderate quantity of alginate (3.5 wt%), and the maximum level of cross-linker (1.00 M).

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