Water-based green media for the synthesis of cellulose acid half-esters: physicochemical characterization and conformation-modulating interactions

This study presents a simple and ecofriendly pathway for synthesizing of cellulose acid half-esters, utilizing a toxic organic solvent-free synthesis strategy and ensuring a green approach. The esterification of hydroxyethyl cellulose (HEC), derived from Stipa tenacissima, with maleic, succinic, and phthalic anhydrides was investigated, revealing significant structural and physicochemical modifications. Increasing the anhydride/HEC molar ratio enhanced the degree of substitution (DS), reaching values of 1.4, 1.28, and 0.51 for HEC-AS, HEC-AM, and HEC-AP, respectively. High reaction temperatures (>100 °C) promoted cross-linking, affecting the solubility of the modified polymers. Structural analysis showed that the organization of acid half-esters strongly influenced wetting properties and thermal behavior. HEC-AM and HEC-AP exhibited lower T_g values (40 °C and 91.82 °C) due to hydrogen bonding reorganization and the resulted configuration of the acid half-ester groups, while HEC-AS remained stable at 117.76 °C. These structural differences resulted in distinct contact angles of 55°, 90°, and 102°, respectively. Solubility and surface charge studies further confirmed the impact of modification on polymer charge behavior, resulting in an anionic character. These findings demonstrate the effectiveness of this green synthesis strategy in tailoring biopolymer properties for functional applications.