Insights into the role of the degree of polymerization in the hydrothermal conversion of cellulose

Hydrothermal conversion of cellulose is a promising route for producing biofuels and value-added chemicals, yet the role of degree of polymerization (DP) in steering reaction pathways remains unclear. In this study, we investigated the DP-dependent variations in the products derived from cellulose under the hydrothermal conversion scenario (DP ranging from 1 to 613 at 280 °C for 60 min) using multiple characterization methods, thereby identifying the role of DP and elucidating the corresponding conversion mechanisms. Results demonstrate that DP critically determines both conversion behavior and product selectivity. Low-DP cellulose favored rapid hydrolysis, generating abundant soluble oxygenated intermediates and promoting the accumulation of liquid-phase organics. The highest total organic carbon and chemical oxygen demand were obtained at DP 12 . These reactive intermediates further underwent liquid-phase repolymerization, leading to the formation of spherical hydrochar. In contrast, high-DP cellulose exhibited restricted depolymerization because of stronger hydrogen-bonding networks and greater chain entanglement, resulting in incomplete degradation and predominant solid-phase condensation that produced compact residues. Overall, DP regulates glycosidic bond accessibility and the subsequent evolution of intermediates, thereby governing the distribution of gas, liquid, and solid products. These findings provide mechanistic insight into DP-dependent hydrothermal pathways and offer an effective strategy for directing cellulose conversion toward target products through feedstock selection and DP regulation.