Upcycling Orange-Based Waste into Functional CNCs for Greener L-Lactide Ring-Opening Polymerization

This study demonstrates the valorization of orange peel waste as a sustainable feedstock for the production of cellulose nanocrystals (CNCs). Compositional analysis revealed a cellulose content up to 10.0% in the raw material. After performing the alkaline/peroxide treatment, CNCs were isolated via acid hydrolysis. Different inorganic acids were compared, namely sulfuric, phosphoric, and hydrochloric acids at low molar concentrations. The resulting CNCs showed distinct morphological and physicochemical properties, with sulfuric acid treatment yielding the highest crystallinity index (TCI) of 0.86 under conditions of 3.0 mol/L, 80 °C, and 225 min. Additionally, the presence of sulfate or phosphate groups significantly influenced the thermal degradation behavior and the inorganic residue content in the obtained CNCs. Finally, the CNCs were successfully tested as co-initiator for lactide ring-opening polymerization. The results show that the molecular weights of the resulting polylactide varied depending on the CNC dispersion. This work supports the use of orange peel waste as a bio-source for CNC production and their potential application as a co-initiator in the synthesis of polyesters.