One-Step Solvent-Free Strategy to Efficiently Synthesize High-Substitution Cellulose Esters

Cellulose esters are promising biobased alternatives to traditional petroleum-derived polymeric materials. However, the conventional chemical esterification of cellulose often involves harsh conditions and complex solubilization or activation steps. Based on our previous ball-milling esterifying method of cellulose, this work developed an improved one-step and solvent-free esterification strategy to synthesize thermoplastic cellulose esters efficiently. By utilizing trifluoroacetic anhydride (TFAA) as the promoter in combination with ball-milling, a series of cellulose esters with a high degree of substitutions (DS) were easily achieved, including linear (long chain), branched, and bulky side-chain esters. Interestingly, the introduction of linear moieties (lauroyl groups) to cellulose not only widened the temperature window for the melt processing but also remarkably improved the ductility. Specifically, the elongation at break enhanced from 2.27% for cellulose stearate esters to 40.99% for lauric acid cellulose laurates. This strategy was shown to be beneficial in terms of both efficiency and low waste, as evidenced by a high esterifying agent/DS ratio of 1.03 and a low E-factor of 0.92–1.48. Furthermore, a new concept of "Q value" was developed to effectively assess the suitability of various esterifying agents for the ball-milling synthesis of high-substitution cellulose esters. This work provided a versatile method for the efficient conversion of intact cellulose to cellulose esters, thereby expanding the potential applications of these biobased materials.