Cellulose microfiber production from green seaweed Ulva lactuca using hydrated deep eutectic solvent.

We investigated the effectiveness of hydrated deep eutectic solvents (DESs) to achieve tunable seaweed cellulose microstructures from Ulva lactuca. Cellulose was extracted via a sequential chemical protocol, then treated with 30% DESs (choline chloride (ChCl) or betaine as hydrogen bond acceptors and urea, citric acid, or oxalic acid as donors) combined with mechanical shearing. While most DESs combinations yielded spherical seaweed cellulose microparticles (dry diameter of 605-777 nm), the ChCl:urea formulation successfully produced seaweed cellulose microfibers (SCMFs). These SCMFs exhibited superior quality (dry diameter of 372 nm), and water dispersibility with a hydrodynamic diameter of 134 nm and a polydispersity index of 0.23. Crucially, the DES composition dictated cellulose structure: ChCl:urea-treated SCMF remained predominantly amorphous, whereas other DESs treatments increased microparticles crystallinity. Furthermore, ChCl:oxalic acid introduced carboxyl functional groups. Selecting appropriate hydrated DESs thus offers a sustainable biotechnology tool to tune cellulose morphology, crystallinity, and surface chemistry.