Unlocking the Role of van der Waals Interactions in Governing the Thermoplasticity of Cellulose Esters

Fatty acid cellulose esters (FACEs) are cellulose thermoplastics with wide application potential. However, the molecular factors governing the thermoplasticity of highly substituted FACEs remain poorly understood. Here, we synthesized a series of FACEs with varied side-chain lengths to clarify the role of intermolecular interactions. Characterization and density functional theory calculations showed that extensive esterification largely disrupted the hydrogen-bonding network, leaving van der Waals interactions (VDW) as the predominant intermolecular interactions. As the side-chain carbon numbers increased from 2 to 8, the Hamaker constant (Apoly/poly) decreased from 9.20 × 10−20 J to 6.04 × 10−20 J, accompanied by decreases in the melt flow temperature (Tf) from >240 °C to 120 °C and glass transition temperature (Tg) from 195 °C to 90 °C. Moreover, strong linear correlations (R2 ≥ 0.91) were established between Apoly/poly and Tg, Tf, providing a quantitative VDW-based framework for understanding the thermoplasticity of highly substituted FACEs.