Cellulose Microfiber Production from Green Seaweed Ulva lactuca Using Hydrated Deep Eutectic Solvent

Purpose We investigated the effectiveness of hydrated deep eutectic solvent (DES) treatments at modulating the morphology of Ulva lactuca cellulose to enable the selective production of seaweed cellulose microfibers (SCMF) with distinct functionality. Methods Ulva lactuca cellulose was extracted by sequential removal of water soluble material, lignin and pigment using hot water, NaOH and H ₂ O ₂ , respectively. The extracted cellulose was then treated by various hydrated DES (30% DES in water) in combination with homogenization and sonication, yielding SCMF. Results Treatment with 30% hydrated DES composed of choline chloride (ChCl) or betaine as hydrogen bond acceptors and urea, citric acid, or oxalic acid as hydrogen bond donors combined with homogenization and sonication successfully produced SCMF. The finest SCMF was obtained using ChCl:urea, yielding fibers with a dry diameter of 371.7 nm. The other DES treatments produced spherical seaweed cellulose microparticles with an average diameter between 605 and 777 nm. The SCMF exhibited exceptional dispersibility in water, with a hydrodynamic diameter of 134.94 nm and good homogeneity, with a polydispersity index of 0.23. Notably, only the ChCl:urea treatment produced a SCMF that remained predominantly amorphous, while all other hydrated DES treatments significantly increased crystallinity. Treatment with ChCl:oxalic acid introduced carboxyl groups into the structure. Conclusion These findings demonstrate tunable cellulose morphology, crystallinity and excellent water dispersibility through selecting appropriate hydrated DES combinations for potential application in sustainable material and functional material systems.