Chitosan’s activities are significantly affected by degree of deacetylation (DDA), while fully deacetylated chitosan is difficult to produce in a large scale. Therefore, this paper introduces a compression method for preparing 100% deacetylated chitosan with less environmental pollution. The product is characterized by XRD, FT-IR, UV and HPLC. The 100% fully deacetylated chitosan is produced in low-concentration alkali and high-pressure conditions, which only requires 15% alkali solution and 1:10 chitosan powder to NaOH solution ratio under 0.11–0.12MPa for 120min. When the alkali concentration varied from 5% to 15%, the chitosan with ultra-high DDA value (up to 95%) is produced

A comprehensive review of melanin's structure, identification methods, and biological activities, highlighting its potential for further development and diverse applications in various fields.